The
Houtman Abrolhos (often informally called the
Abrolhos Islands) is a chain of 122 islands, and associated
coral reefCoral reefs are aragonite structures produced by living organisms, found in marine waters containing few nutrients. In most reefs, the predominant organisms are stony corals, colonial cnidarians that secrete an exoskeleton of calcium carbonate...
s, in the
Indian OceanThe Indian Ocean is the third largest of the world's oceanic divisions, covering about 20% of the water on the Earth's surface. It is bounded on the north by South Asia ; on the west by Africa; on the east by Indochina, the Sunda Islands, and Australia; and on the south by the Southern Ocean...
off the west coast of Australia. Nominally located at , it lies about eighty kilometres (50 mi) west of
Geraldton, Western AustraliaGeraldton is a city and port in Western Australia located north of Perth. According to the 2006 census, Geraldton has a population of 31,553, making it the fourth-largest city in Western Australia....
. It is the southernmost true coral reef in the Indian Ocean, and one of the highest latitude reef systems in the world. It is one of the world's most important
seabirdSeabirds are birds that have adapted to life within the marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same environmental problems and feeding niches have resulted in similar adaptations...
breeding sites, and is the centre of Western Australia's largest single species fishery, the
Western Rock LobsterPanulirus cygnus is a species of spiny lobster , found off the west coast of Australia. Panulirus cygnus is the basis of Australia's most valuable fishery, making up 20% of value of Australia's total fishing industry, and is identified as the western rock lobster.The species has five pairs of legs...
fishery. It is also well known as the site of numerous
shipwreckA shipwreck is the remains of a ship that has wrecked, it having either been sunk or beached. A shipwreck can refer to a wrecked ship or to the event that caused the wreck, such as the striking of something that causes the ship to sink, the stranding of the ship on rocks, land or shoal, or the...
s, the most famous being the
DutchThe Netherlands is a country in Northwestern Europe, constituting the major portion of the Kingdom of the Netherlands. It is a parliamentary democratic constitutional monarchy. The Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east...
ships
BataviaBatavia was a ship of the Dutch East India Company . She was built in Amsterdam in 1628, and had 24 cast-iron cannons. Batavia was shipwrecked on her maiden voyage, and made famous by the subsequent mutiny and massacre that took place among the survivors...
, which was wrecked in 1629, and
ZeewijkThe Zeewijk was an 18th century East Indiaman of the Dutch East India Company that was shipwrecked at the Houtman Abrolhos, off the coast of Western Australia, on 9 June 1727. The survivors built a second ship, the Sloepie, enabling 82 out of the initial crew of 208 to reach their initial...
, wrecked in 1727.
Geography
The Houtman Abrolhos is made up of three island groups, the
Wallabi GroupThe Wallabi Group is the northern-most group of islands in the Houtman Abrolhos. Nominally located at , it is 58 kilometres from the Australian mainland, and about 9 kilometres from the Easter Group....
,
Easter GroupThe Easter Group is the central of three groups of islands that make up the Houtman Abrolhos island chain. Nominally located at , it is about 20 kilometres by 12 kilometres, and consists of a number of islands including Rat Island, Wooded Island, Morley Island, Suomi Island and Alexander Island...
and
Pelsaert GroupThe Pelsaert Group is the southernmost of the three groups of islands that make up the Houtman Abrolhos island chain. Nominally located at , it consists of a number of islands, the largest of which are Gun Island, Middle Island, and Pelsaert Island. The group is named after a dutch "opperkoopman"...
.
The most northerly group, the Wallabi Group, consists of an island clump about 17 kilometres (10 mi) by 10 kilometres (6 mi), and also takes in the outlying
North IslandNorth Island is the northernmost island in the Houtman Abrolhos, a coral reef archipelago in the Indian Ocean off the coast of Mid West Western Australia. Located approximately 14 km from the nearest island group, it is one of the largest islands in the Houtman Abrolhos, and is of the few to...
, located 14 kilometres to the northwest. The main islands of the Wallabi Group are North Island,
West Wallabi IslandWest Wallabi Island is an island in the Wallabi Group of the Houtman Abrolhos, located in the Indian Ocean off the west coast of mainland Australia.-History:...
,
East Wallabi IslandEast Wallabi Island is an island in the Wallabi Group of the Houtman Abrolhos, located in the Indian Ocean off the west coast of mainland Australia.-History:East Wallabi Island played an important role in the story of the Batavia shipwreck and massacre...
and Beacon Island. The group is best known for the shipwreck of the
BataviaBatavia was a ship of the Dutch East India Company . She was built in Amsterdam in 1628, and had 24 cast-iron cannons. Batavia was shipwrecked on her maiden voyage, and made famous by the subsequent mutiny and massacre that took place among the survivors...
on Morning Reef near Beacon Island in 1629, and the subsequent
mutinyMutiny is a conspiracy among members of a group of similarly-situated individuals to openly oppose, change or overthrow an existing authority...
and massacre that took place among the
maroonedMarooning is leaving someone behind on purpose in an uninhabited area, such as an uninhabited island. The word appears in writing in approximately 1709, and is derived from the term maroon, a word for a fugitive slave, which could be a corruption of Spanish cimarrón, meaning "wild".The practice...
survivors.
The Easter Group lies to the southeast of the Wallabi Group, from which it is separated by a 9 kilometres (5 mi) wide channel named Middle Channel. It is about 20 kilometres by 12 kilometres, and consists of a number of islands including Rat Island, Wooded Island, Morley Island, Suomi Island and
Alexander IslandAlexander Island is one of the five largest islands in the Easter Group of the Houtman Abrolhos. It is nominally located at...
.
Further to the southeast, across Zeewijk Channel, lies the Pelsaert Group, the most southerly true coral reef in the Indian Ocean. The main islands of this group are Middle Island, Square Island, Long Island, Pelsaert Island, Basile Island and the Mangrove Group. A great many ships have been wrecked in the Pelsaert Group, most notably the
ZeewijkThe Zeewijk was an 18th century East Indiaman of the Dutch East India Company that was shipwrecked at the Houtman Abrolhos, off the coast of Western Australia, on 9 June 1727. The survivors built a second ship, the Sloepie, enabling 82 out of the initial crew of 208 to reach their initial...
, which was wrecked on the Half Moon Reef in 1727, the survivors staying on
Gun IslandGun Island is one of the larger islands in the Pelsaert Group of the Houtman Abrolhos. It is nominally located at , about 4 km north and east of Half Moon Reef and is a flat limestone outcrop of about by in size....
for some time afterwards. Other wrecks include the
Ocean Queen, wrecked on the Half Moon Reef in 1842; the
Ben Ledi, wrecked off Pelsaert Island in 1879; and the
WindsorThe Windsor was a ship wrecked on Long Reef near Sydney, Australia in 1816.The Windsor was a sloop of 22 tons owned and under the command of Henry Major. The Windsor left the Hawkesbury and headed for Sydney when it was blown well off shore by a gale. It is probable that it was this gale that...
, wrecked on the Half Moon Reef in 1908.
Discovery and naming
According to the surviving historical record, the first sighting of the Houtman Abrolhos was by the
DutchThe Netherlands is a country in Northwestern Europe, constituting the major portion of the Kingdom of the Netherlands. It is a parliamentary democratic constitutional monarchy. The Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east...
VOCThe Dutch East India Company was a chartered company established in 1602, when the States-General of the Netherlands granted it a 21-year monopoly to carry out colonial activities in Asia. It was the first multinational corporation in the world and the first company to issue stock...
ships
Dordrecht and
Amsterdam in 1619, only three years after
Dirk HartogDirk Hartog was a 17th century Dutch sailor and explorer. Dirk Hartog's expedition was the second European group to land on Australian soil. He left behind an artefact to record his visit, the Hartog plate. His name is sometimes alternately spelled Dirk Hartog, Dirck Hartog or Dirch Hartichs...
made the first authenticated sighting of what is now Western Australia, and only 13 years after the first authenticated voyage to Australia, that of the
DuyfkenDuyfken was a small Dutch ship built in the Netherlands. She was a fast, lightly-armed ship probably intended for shallow water, small valuable cargoes, bringing messages, sending provisions, or privateering...
in 1606. Discovery of the islands was credited to
Frederick de HoutmanFrederick de Houtman , or Frederik de Houtman, was a Dutch explorer who sailed along the Western coast of Australia en route to Batavia.-Biography:Frederick de Houtman was born in 1571 in Gouda, Holland, Seventeen Provinces....
, Captain-General of the
Dordrecht, as it was Houtman who later wrote of the discovery in a letter to the directors of the
Dutch East India CompanyThe Dutch East India Company was a chartered company established in 1602, when the States-General of the Netherlands granted it a 21-year monopoly to carry out colonial activities in Asia. It was the first multinational corporation in the world and the first company to issue stock...
:
The word
Abrolhos is of
PortuguesePortuguese is a Romance language that originated in what is now Galicia and northern Portugal. It is derived from the Latin spoken by the romanized Pre-Roman peoples of the Iberian Peninsula around 2000 years ago...
origin, making the Houtman Abrolhos one of only two Australian places with a Portuguese name, the other being Pedra Branca in
TasmaniaTasmania is an Australian island and state. It is located south of the eastern side of the continent, from which it is separated by Bass Strait. The state includes the island of Tasmania – the 26th largest island in the world – and the surrounding islands. The state has a population of 500,000 ,...
. The term is commonly reported to be a contraction of the Portuguese expression
abro olhos ("open the eyes") or
abri vossos olhos ("keep your eyes open"), but this has been shown to be a
false etymologyA false etymology is any assumed or postulated etymology that is incorrect.Folk etymology, in its basic sense, refers to popularly held beliefs about the origins of specific words, especially where these originate in "common-sense" assumptions rather than serious research...
. In the Portuguese language of the time,
abrolhos meant "spiked obstructions", and served not only as a word for offshore reefs, but also as their word for
caltropA caltrop is an antipersonnel weapon made up of two or more sharp nails or spines arranged in such a manner that one of them always points upward from a stable base...
s and
chevaux de friseThe cheval de frise was a Medieval defensive obstacle consisting of a portable frame covered with many long iron or wooden spikes or even actual spears. They were principally intended as an anti-cavalry obstacle but could also be moved quickly to help block a breach in another barrier...
. To
SpanishSpanish or Castilian is a Romance language in the Ibero-Romance group that originated in northern Spain and gradually spread in the Kingdom of Castile, evolving into the principal language of government and trade in the Iberian peninsula...
ears, however, the word sounded like
abre ojos ("open your eyes"), so they imputed this meaning, and this false etymology was later borrowed by English, Dutch and French writers.
Another explanation has been proferred by Philippe Godard. He reports, without citation, that some authors have claimed that the word
Abrolhos comes from a 15th century Portuguese nobleman named Frederico de Abrolhos. Godard notes, however, that there is no trace of such a person in
LusitaniaLusitania was an ancient Roman province including approximately all of modern Portugal south of the Douro river and part of modern Spain . It was named after the Lusitani or Lusitanian people...
n archives, and that
Abrolhos is not known as a family name in Portugal, making this an unconvincing explanation.
Why Houtman named the islands using a Portuguese word remains a subject of debate. John Forsyth states that the islands are named after the Abrolhos Archipelago off the east coast of
BrazilBrazil , officially the Federative Republic of Brazil , is a country in South America. It is the fifth largest country by geographical area, occupying nearly half of South America, the fifth most populous country, and the fourth most populous democracy in the world. Bounded by the Atlantic Ocean...
, which was discovered and named by Portuguese navigators early in the 16th century. This position is supported by the fact that Houtman was familiar with the Abrolhos Archipelago, having sailed through it in 1598. Others assert that
abrolhos was a Portuguese
lookoutA lookout or look-out is a person on a ship in charge of the observation of the sea for hazards, other ships, land, etc. Lookouts report anything they see and or hear. When reporting contacts, lookouts give information such as, bearing of the object, which way the object is headed, target angles...
's cry which, like many other Portuguese maritime terms, was taken up by sailors of other nationalities, becoming by Houtman's time a Dutch loan word for offshore reefs. Finally, it has been argued by proponents of the
theory of Portuguese discovery of AustraliaAlthough most historians hold that the European discovery of Australia began in 1606 with the voyage of the Dutch navigator Willem Janszoon on board the Duyfken, a number of alternative theories have been put forward. Precedence of discovery has been claimed for China, Portugal, France, Spain and...
that the Portuguese name is evidence that the islands were charted by Portuguese navigators in the 16th century.
Kenneth McIntyreKenneth Gordon McIntyre OBE was an Australian lawyer, historian and mathematician who is perhaps best known for his controversial book The Secret Discovery of Australia - Portuguese ventures 200 years before Captain Cook....
, for example, claimed that Houtman was in possession of Portuguese maps of the west coast of Australia, and that he named the islands "abrolhos" in accordance with the name on his map. Charting of the islands was previously credited to
Jorge de MenezesJorge de Menezes was a Portuguese explorer who in 1526-27 landed on Waigeo Island , taking shelter in the town of Wasai whilst he awaited the passing of the monsoon season...
, but the notion that Menezes visited Australia is now thoroughly discredited, and no other candidate has been proffered.
The primary piece of evidence for the claim of Portuguese priority is the 16th century
Dieppe mapsThe Dieppe maps are a series of world maps produced in Dieppe, France, in the 1540s, 1550s and 1560s. They are large hand-produced maps, commissioned for wealthy and royal patrons, including Henry II of France and Henry VIII of England...
, some of which are said to show the west coast of Australia, including an island at the position of the Houtman Abrolhos. This island is unlabelled on most of the Dieppe maps, but on
Pierre DesceliersPierre Desceliers was a French cartographer of the Renaissance and an eminent member of the Dieppe School of Cartography. He is considered to be the father of French hydrography....
' 1550 map, it is labelled
Arenes. In 1895,
George CollingridgeGeorge Collingridge was an Australian writer and illustrator best known today for his early assertions of Portuguese discovery of Australia in the 16th century....
suggested that
Arenes was a corruption of
Abrolhos, but this was mocked by Heeres in 1898, and according to J. S. Battye "this suggestion can scarcely be regarded seriously. It certainly does not in any way add to the merit of the Portuguese claim".
Setting aside the Portuguese claims, the Houtman Abrolhos first appears on a published map in 1622, on a little-known portolan by
Hessel GerritszHessel Gerritsz was a Dutch engraver, cartographer and publisher. Despite strong competition, he is considered by some “unquestionably the chief Dutch cartographer of the 17th century”...
. They are unlabelled, however, being marked merely as a group of small circles. They are first named in print in Gerritsz' 1627 map
Caert van't Landt van d'EendrachtCaert van't Landt van d'Eendracht is a 1627 map by Hessel Gerritsz. One of the earliest maps of Australia, it shows what little was then known of the west coast, based on a number of voyages beginning with the 1616 voyage of Dirk Hartog.The map is oriented with north roughly to the left...
, where they bear the label
Fr. Houtman's abrolhos. On a map produced by him the following year, they are labelled
Houtman's Abrolhos.
On British Admiralty charts, the islands are labelled
Houtman's Rocks.
Wreck of the Batavia
In 1629 some of the islands were the scene of a spectacular shipwreck and mutiny. The Dutch ship
BataviaBatavia was a ship of the Dutch East India Company . She was built in Amsterdam in 1628, and had 24 cast-iron cannons. Batavia was shipwrecked on her maiden voyage, and made famous by the subsequent mutiny and massacre that took place among the survivors...
under the command of
Francisco PelsaertFrancisco Pelsaert was a Dutch merchant who worked for the Dutch East India Company, who became most famous as the commander of the ship Batavia, which ran aground in the Houtman Abrolhos off the coast of Western Australia in June...
ran aground and Pelsaert and some men went in an open boat to the town of Batavia (now
JakartaJakarta is the capital and largest city of Indonesia. It also has a greater population than any other city in Southeast Asia. It was formerly known as Sunda Kelapa , Jayakarta , Batavia , and Djakarta . Located on the northwest coast of Java, it has an area of and a population of 8,489,910...
) in order to get help. A group of the men who stayed on some of the islets decided to terrorise and massacre many others, including women. When Pelsaert came back many culprits were executed.
Wreck of the Zeewijk
The
ZeewijkThe Zeewijk was an 18th century East Indiaman of the Dutch East India Company that was shipwrecked at the Houtman Abrolhos, off the coast of Western Australia, on 9 June 1727. The survivors built a second ship, the Sloepie, enabling 82 out of the initial crew of 208 to reach their initial...
was the last of the four Dutch East Indiamen to be wrecked on the west coast of Australia. The Ship's Council having made the inexplicable decision to disregard sailing orders and actually seek out the west coast of Australia, the ship ran onto the Half Moon Reef at about 7:30pm on 9 June 1727. It did not break up immediately, and the heavy swell made evacuation impossible until 18 June. The
longboatIn the days of sailing ships, a vessel would carry several boats for various uses. One would be a longboat, an open boat to be rowed by eight or ten oarsmen, two per thwart. In other words the longboat was double banked: its rowing benches were designed to accommodate two men...
was launched on that day, and the crew and stores were thereafter gradually transferred to nearby
Gun IslandGun Island is one of the larger islands in the Pelsaert Group of the Houtman Abrolhos. It is nominally located at , about 4 km north and east of Half Moon Reef and is a flat limestone outcrop of about by in size....
. Later, the men landed ten chests of money, containing 315,836
guilderGuilder is the English translation of the Dutch gulden — from Old Dutch for 'golden'. The guilder originated as a gold coin but has been a common name for a silver or base metal coin for some centuries...
s and weighing a total of three tons.
The crew of the
Zeewijk would be marooned in the Pelsaert Group for ten months, during which time they lived off seals, seabirds, eggs, and victuals salvaged from the wreck. They obtained some water from rainfall, but were forced to explore throughout the group in search of further supplies. A great many men died on the islands, including two boys who were accused of
sodomySodomy is a term used today predominantly in law to describe the act of anal intercourse, oral intercourse, or bestiality.- Definitions :...
and marooned on separate islands of the Mangrove Group.
On 10 July the longboat, fitted for a voyage and crewed with eleven men, was sent to
BataviaBatavia is the Latin name for the land of the Batavians during Roman times. This was roughly the area around the city of Nijmegen within the Roman Empire. The remainder of this land is nowadays known as Betuwe. During the Renaissance, Dutch historians tried to promote these Batavians to the status...
to obtain help. It never arrived there, and nothing is known of its fate. Four months later the castaways began building a boat, sufficient to carry all the men and the money chests. Completed in March 1728 and affectionately named the
Sloepie ("little
sloopA sloop is a sailboat with a fore-and-aft rig and a single mast farther forward than the mast of a cutter. A sloop's fore-triangle is smaller than a cutter's, and unlike a cutter, a sloop usually bends only one headsail, though this distinction is not definitive; some sloops such as the...
"), it was the first ocean-going vessel built in Australian history. On 26 March 1728, the surviving men set sail for Batavia, arriving in
Sunda StraitThe Sunda Strait is the strait between the Indonesian islands of Java and Sumatra. It connects the Java Sea to the Indian Ocean...
late the following month.
Later history
During admiralty surveys of the north west coast in 1840, crew from
HMS BeagleHMS Beagle was a Cherokee class 10-gun brig-sloop of the Royal Navy, named after the beagle, a breed of dog. She was launched on 11 May 1820 from the Woolwich Dockyard on the River Thames, at a cost of £7,803...
discovered a brass gun of about three pounds calibre, an iron swivel on which paint still adhered as well as numerous other artefacts signifying European occupation, on the largest island in the Pelsart Group. The commander,
John Clements WickhamJohn Clements Wickham was a naval officer and judge. He was a Lieutenant on HMS Beagle during her second survey mission from 1831 to 1836, which took the young naturalist Charles Darwin on what became the subject of his book, The Voyage of the Beagle...
, named the place
Gun IslandGun Island is one of the larger islands in the Pelsaert Group of the Houtman Abrolhos. It is nominally located at , about 4 km north and east of Half Moon Reef and is a flat limestone outcrop of about by in size....
and the passage between the Easter and Pelsart Groups, Zeewijk Channel.Later during the 19th century many islets were used by men collecting
guanoGuano is the excrement of seabirds, bats, and seals. Guano manure is an effective fertilizer and gunpowder ingredient due to its high levels of phosphorus and nitrogen and also its lack of odor. Superphosphate made from guano is used for aerial topdressing...
.
Tenure, governance and management
The Houtman Abrolhos is Australian territory. There is no dispute about this, although it has been suggested that Australia claims the island chain under the UNCLOS by extending their continental baseline to encompass it, a breach of Article 7 of the Convention.
The islands are a part of Western Australia. They are part of the
Electoral district of GeraldtonGeraldton is an electoral district of the Legislative Assembly in the Australian state of Western Australia.Geraldton was one of the original 30 seats contested at the 1890 state election...
, and the
Shire of NorthamptonThe Shire of Northampton is a Local Government Area in the Mid West region of Western Australia, about north of Geraldton and about north of the state capital, Perth...
.
Management is vested in the Department of Fisheries.
Geology
Some of the islands are considered to be remnants of the mainland isolated by rising sea level during the last 8,000 to 10,000 years. Others were more recently formed from
coralCorals are marine organisms from the class Anthozoa and exist as small sea anemone-like polyps, typically in colonies of many identical individuals...
rubble.
Bathymetry
The Houtman Abrolhos lays in the
Indian OceanThe Indian Ocean is the third largest of the world's oceanic divisions, covering about 20% of the water on the Earth's surface. It is bounded on the north by South Asia ; on the west by Africa; on the east by Indochina, the Sunda Islands, and Australia; and on the south by the Southern Ocean...
about 60 kilometres (40 mi) off the coast of Western Australia, near the edge of Australia's
continental shelfThe continental shelf is the extended perimeter of each continent and associated coastal plain, and was part of the continent during the glacial periods, but is undersea during interglacial periods such as the current epoch by relatively shallow seas and gulfs. The continental rise is below the...
. At less than 50 metres (160 ft) deep, the shelf is quite shallow. It is also fairly level, the depth increasing to the west at a modest gradient of about 1.3 metres per kilometre (7 ft/mi). About five kilometres (3 mi) to the west of the Houtman Abrolhos lies the shelf break, beyond which the seabed falls away much more steeply, averaging around 50 metres per kilometre (260 ft/mi).
The islands of each island group arise from a single
carbonate platformA carbonate platform is a sedimentary body which possesses topographic relief, and is composed of autochthonous calcareous deposits . Platform growth is mediated by sessile organisms whose skeletons build up the reef or by organisms which induce carbonate precipitation through their metabolism...
, so the waters within an island group are mostly shallow. The channels between groups, however, are 40 to 50 metres deep, and therefore no impediment to the exchange of offshore and inshore waters.
Currents
The Houtman Abrolhos lies almost directly in the path of the
Leeuwin CurrentThe Leeuwin Current is a warm ocean current which flows southwards near the western coast of Australia. It rounds Cape Leeuwin to enter the waters south of Australia where its influence extends as far as Tasmania...
, which draws warm, low-saline water of tropical origin southwards along the coast of Western Australia. This current flows all year round, but is strongest during
southern hemisphereThe Southern Hemisphere is the half of a planet that is south of the equator—the word hemisphere literally means 'half ball'...
winter months. In general the Leeuwin Current runs along the shelf break, and thus passes close by the western edge of the Abrolhos. It meanders, however, sometimes passing well out to sea, and sometimes passing directly through the island chain, bathing it in warm tropical water; Although the direction of the Leeuwin Current is predominantly southerly,
Shark BayShark Bay is a world heritage site in the Gascoyne region of Western Australia. It is an area centered approximately on , 800 kilometres north of Perth, on the westernmost point of Australia. An expedition led by Dirk Hartog happened upon the area in 1616, becoming the second group of Europeans...
and the Houtman Abrolhos together act as a
topographicalTopography is the study of Earth's surface shape and features or those ofplanets, moons, and asteroids...
trigger for the forming of
eddiesIn fluid dynamics, an eddy is the swirling of a fluid and the reverse current created when the fluid flows past an obstacle. The moving fluid creates a space devoid of downstream-flowing fluid on the downstream side of the object...
, so the Abrolhos can experience currents from any direction, even when the Leeuwin Current is flowing strongly.
Unlike most other major ocean currents, there is no large-scale coastal upwelling associated with the
Leeuwin CurrentThe Leeuwin Current is a warm ocean current which flows southwards near the western coast of Australia. It rounds Cape Leeuwin to enter the waters south of Australia where its influence extends as far as Tasmania...
. There is limited evidence for some sporadic, localised upwelling in the vicinity of the Abrolhos, but if so it appears to have little effect on the extremely low levels of nutrients in the water.
Temperature and salinity
Sea temperature at the islands varies according to a diurnal cycle, with the water at its coldest between six and eight in the morning, and at its warmest between three and four in the afternoon. In summer the daily temperature range is around 1 °C (2 °F); in winter it is about half that.
There is also an annual cycle, with sea temperature varying by a little less than 4 °C (7 °F) over the year, peaking at nearly 24 °C (75 °F) in March, and falling to around 20 °C (68 °F) in September. This variability is much less than in nearby coastal waters, which reaches a similar peak in summer but drops as low as 18 °C (64 °F) in winter. The relatively low variability in sea temperatures at the Abrolhos is largely attributable to the Leeuwin Current, which bathes the islands in warm tropical water during winter months.
A similar annual pattern occurs in
salinitySalinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...
. There is a clear seasonal variation, with values ranging from a summer high of around 35.7 ppt, to a winter low of around 35.4 ppt. As with water temperatures, the variability in salinity is much smaller than in coastal waters, where summer salinity reaches 36.4 ppt. This difference is partly due to the low-salinity waters of the Leeuwin Current, but there are a number of other factors involved, including high evaporation of coastal waters in summer.
Temperatures can also vary substantially from year to year. Annual mean temperatures vary by as much as 1 °C (2 °F); with cooler years usually cooler throughout the year. There is evidence that annual mean temperatures are related to
El Niño-Southern OscillationEl Niño-Southern Oscillation is a periodic change in the atmosphere and ocean of the tropical Pacific region. It is defined in the atmosphere by the sign of the pressure difference between Tahiti and Darwin, Australia, and in the ocean by warming or cooling of surface waters of the tropical central...
events.
The water column is generally well-mixed, with no evidence of a significant
haloclineIn oceanography, a halocline is a strong, vertical salinity gradient. Because salinity affects the density of seawater, it can play a role in its vertical stratification...
or
thermoclineThe thermocline is a thin but distinct layer in a large body of fluid , in which temperature changes more rapidly with depth than it does in the layers above or below...
. Mean differences in water temperature between sea surface and sea bed range from only half a degree (Celsius; 1 °F) in summer to almost zero in winter, and differences in salinity are very small even when the Leeuwin Current is at its strongest.
Sea levels
As with the rest of southwestern Australia,
tideTides are the rises and falls of sea level caused by the combined effect of rotation of the Earth and the gravitation of the Moon and the Sun. The tides occur with a period of approximately 12 and a half hours and are influenced by the shape of the near-shore bottom.Most coastal areas experience...
s at the Houtman Abrolhos are small and irregular. There is little tidal data available for the islands, but what there is accords very closely with the data for Geraldton. Geraldton tides follow a diurnal pattern, with maximum tidal ranges of around 1 metre (3 ft).
Mean sea levels at Geraldton show seasonal fluctuations, being higher in winter when the Leeuwin Current is at its peak. There are also variations from year to year, which are strongly associated with the
El Niño-Southern OscillationEl Niño-Southern Oscillation is a periodic change in the atmosphere and ocean of the tropical Pacific region. It is defined in the atmosphere by the sign of the pressure difference between Tahiti and Darwin, Australia, and in the ocean by warming or cooling of surface waters of the tropical central...
(ENSO) cycle. Apparently, ENSO events induce a weaker Leeuwin Current, which results in lower sea levels.
There is no published information on wave heights in the Abrolhos. In the open ocean, waves are typically a little over two metres high all year round. Nearer the mainland, they are usually less than 1.2 metres, with a calmer period in March and April, and another in October and November.
Climate
As of 2007, the Australian
Bureau of MeteorologyThe Bureau of Meteorology is an Executive Agency of the Australian Government responsible for providing weather services to Australia and surrounding areas. It was established in 1906 under the Meteorology Act, and brought together the state meteorological services that existed before then...
has not published
climaticClimate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and numerous other meteorological elements in a given region over long periods of time...
data for the Houtman Abrolhos. However, an
automatic weather stationAn automatic weather station is an automated version of the traditional weather station, either to save human labour or to enable measurements from remote areas...
has been installed on
North IslandNorth Island is the northernmost island in the Houtman Abrolhos, a coral reef archipelago in the Indian Ocean off the coast of Mid West Western Australia. Located approximately 14 km from the nearest island group, it is one of the largest islands in the Houtman Abrolhos, and is of the few to...
since 1990, and hourly measures of
precipitationIn meteorology, precipitation is any product of the condensation of atmospheric water vapor that is deposited on the Earth's surface. The main forms of precipitation include rain, snow, ice pellets, and graupel...
, air temperature,
wind speedWind speed is the speed of wind, the movement of air or other gases in an atmosphere. It is a scalar quantity, the magnitude of the vector of motion....
,
wind directionWind direction is the direction from which a wind originates. It is usually reported in cardinal directions or in azimuth degrees.There are a variety of instruments used to measure wind direction, such as the windsock and wind vane. Both of these instruments work by moving to minimize air resistance...
,
relative humidityRelative humidity is a term used to describe the amount of water vapor that exists in a gaseous mixture of air and water vapor.- Definition :...
and
atmospheric pressureAtmospheric pressure is defined as the force per unit area exerted against a surface by the weight of air above that surface at any given point in the Earth's atmosphere. In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above...
have been publicly available since then. Based on this and other data, researchers have put together a picture of the Abrolhos' climate.
The islands have a
Mediterranean climateA hi Mediterranean climate resembles the climate of the lands in the Mediterranean Basin, which includes most of the area with this climate type worldwide...
, with warm dry summers and cooler, wet winters. Mean temperatures range from 9.3 °C to 19.5 °C in July, and from 19.1 °C to 32.4 °C in February. These temperatures have a substantially smaller range than on the mainland: the summer temperature is typically a degree cooler, while winter temperatures are a good deal warmer. This is due to the influence of the ocean, and to the Leeuwin Current.
86% of the rain falls between April and September; on average there are 89 raindays, resulting in 469 millimetres of rain. The wettest month is June, when over 100 millimetres typically falls. In contrast, only about 70 millimetres can be expected to fall between October and March.
It is nearly always windy. During summer a high pressure ridge lies to the south, causing persistent winds from the southeast or southwest, at speeds exceeding 17 knots (31 km/h) almost half the time. During autumn and winter, the ridge moves northwards, increasing the atmospheric pressure over the islands, resulting in highly variable winds. Winter tends to produce both the strongest gales and the most frequent periods of calm.
In addition to these winds, there is daily pattern of land breezes in the morning, followed by the onset of south-westerly sea breezes in the afternoon. This pattern is caused by temperature differences between the land and the ocean, and is not as strong in the Houtman Abrolhos as on the mainland, but is present nonetheless.
Three classes of storm have been identified for the region. Brief squalls may occur between December and April. A
tropical cycloneA tropical cyclone is a storm system characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclones feed on heat released when moist air rises, resulting in condensation of water vapor contained in the moist air...
occurs in the area about once in three years, between January and April; these may generate extremely high wind speeds that are potentially destructive. During winter, extra-tropical cyclones sometimes pass south of Geraldton, generating winter gales with gusts of up to 35 metres per second, the wind direction from the northwest initially, then gradually moving around to southerly.
Biogeography
Under the
Interim Biogeographic Regionalisation for AustraliaThe Interim Biogeographic Regionalisation for Australia is a biogeographic regionalisation of Australia developed by the Australian Government's Department of the Environment, Water, Heritage and the Arts...
(IBRA), the islands of the Houtman Abrolhos fall within the Geraldton Hills subregion of the
Geraldton SandplainsGeraldton Sandplains is an Interim Biogeographic Regionalisation for Australia region in Western Australia.It has two sub regions: -* Geraldton Hills sub region* Lesuer sub region-Further reading:...
region. The main
biogeographicBiogeography is the study of the distribution of biodiversity over space and time. It aims to reveal where organisms live, and at what abundance....
significance of the islands is their isolation, allowing them to provide
refugiaIn biology a refugium is a location of an isolated or relict population of a once widespread species.This isolation can be due to climatic changes or human activities such as deforestation and over-hunting...
for such threatened fauna as
Tammar WallabiesThe Tammar Wallaby , also known as the Dama Wallaby or Darma Wallaby, is a small member of the kangaroo family and is the type species for research on kangaroos and marsupials....
(
Macropus eugenii),
Australian Sea LionThe Australian Sea Lion is a species of sea lion that breeds only on the south and west coasts of Australia. Today there are about 10,000 Australian Sea Lions following the introduction of the Australian National Parks and Wildlife Act of 1972 which prohibited a harvest that began in earnest as...
s (
Neophoca cinerea) and rare breeding seabirds.
In marine terms, the Houtman Abrolhos is located within the
Southwest Shelf TransitionSouthwest Shelf Transition is a marine biogeographic region of Australia. It was referred to as South Western Biotone in Integrated Marine and Coastal Regionalisation of Australia Version 3.3, and as Southwest IMCRA Transition in the National Marine Bioregionalisation of Australia...
, an
Integrated Marine and Coastal Regionalisation of AustraliaThe Integrated Marine and Coastal Regionalisation of Australia , formerly the Interim Marine and Coastal Regionalisation for Australia, is a biogeographic regionalisation of the oceanic waters of Australia's Exclusive Economic Zone...
(IMCRA)
biotoneA biotone is a biogeographical region characterised not by distinctive biota but rather by a distinctive transition from one set of biota to another...
that takes in the continental shelf from
PerthPerth is the capital and largest city of the Australian state of Western Australia. With a population of 1,650,000 , Perth ranks fourth amongst the nation's cities, with a growth rate consistently above the national average....
to
GeraldtonGeraldton is a city and port in Western Australia located north of Perth. According to the 2006 census, Geraldton has a population of 31,553, making it the fourth-largest city in Western Australia....
. This province is defined as the area of shelf where tropical waters intergrade into temperate, thus supporting both tropical and temperate biota. In addition, this area contains the highest concentration of west coast endemics.
Consistent with this, the Houtman Abrolhos contains a mix of tropical, temperate and west coast endemic fauna, resulting in unusual associations such as the occurrence of tropical corals in close association with temperate macro-algae. The proportions of tropical, temperate and west coast endemic biota vary from taxonomic group to group, but in general the biota is dominated by tropical species. This is attributable to the location of the Houtman Abrolhos at the northern limit of the Southwest Shelf Transition, together with the warming influence of the Leeuwin Current.
Under IMCRA, the Southwest Shelf Transition divides into two meso-scale bioregions. One is named
Abrolhos Islands, and covers the shelf waters surrounding the Houtman Abrolhos, with an area of 6,645 square kilometres. The other bioregion, Central West Coast, covers the remaining area.
Terrestrial flora
The flora of the Houtman Abrolhos islands is generally the same as the coastal flora of the adjacent mainland, with the exception of the islands' mangrove, saltbush and salt lake vegetation.
Flora
The
vascular floraVascular plants are those plants that have lignified tissues for conducting water, minerals, and photosynthetic products through the plant. Vascular plants include the ferns, clubmosses, flowering plants, conifers and other gymnosperms...
of the Houtman Abrolhos has been thoroughly surveyed, and species lists have been published for 119 islands. As of 2001, these lists totaled 239 species from 68 families. A further six species have been collected in the Houtman Abrolhos, but cannot be allocated to islands because insufficient location information was recorded. There have also been collections of
mossMosses are small, soft plants that are typically 1–10 cm tall, though some species are much larger. They commonly grow close together in clumps or mats in damp or shady locations. They do not have flowers or seeds, and their simple leaves cover the thin wiry stems...
es,
liverwortHepatica is a genus of herbaceous perennial plants belonging to the buttercup family, Ranunculaceae. A native of central and northern Europe, Asia and northeastern North America, Hepatica is sometimes called liverleaf or "liverwort". It should not be confused with liverworts, which may also be...
s and
lichenLichens are composite organisms consisting of a symbiotic association of a fungus with a photosynthetic partner , usually either a green alga or cyanobacterium...
s, but no information has been published on these non-vascular groups.
The islands with the greatest floristic diversity are East and West Wallabi Islands, with 124 and 97 species respectively. 54 species occur in all three island groups. The most widely distributed species are
Nitraria billardiereiNitraria billardierei is a perennial salt tolerant shrub. It is often found in saline areas or areas that have been overgrazed. Nitre Bush flowers mainly in spring with small ovoid or oblong fruit that are purple, red or golden...
(Nitre Bush), which has been recorded on 106 islands; the exotic
Mesembryanthemum crystallinumMesembryanthemum crystallinum is a prostrate succulent plant that is native to Africa, Western Asia and Europe. The plant is covered with large, glistening bladder cells, reflected in its common names of Common Ice Plant, Crystalline Iceplant or Iceplant.-Uses:Its leaves are edible, as with other...
(Iceplant), on 88 islands;
Threlkeldia diffusaThrelkeldia diffusa, also known as Coast Bonefruit, is a perennial herb which occurs in coastal areas and saline flats in Australia. It is sometimes prostrate or may grow up to 0.4 metres in height. The green flowers occur between October and November in its native range....
(Coast Bonefruit), on 72 islands; and
Atriplex cinereaAtriplex cinerea is a species of plant in the Chenopodiaceae family. It occurs in sheltered coastal areas and around salt lakes in the Australian states of Western Australia, South Australia, Tasmania, Victoria and New South Wales....
(Grey Saltbush), on 70 islands. On the other hand,
Eucalyptus orariaEucalyptus oraria, also known as Ooragmandee, is a mallee species of Eucalyptus that is native to Western Australia, occurring in coastal and near-coastal areas. Its mature height ranges from 1 to 15 metres....
(Ooragmandee) and
Acacia didymaAcacia didyma is a shrub or small tree which is native to Western Australia. It grows to between 1.5 metres and 4 metres in height and flowers from August to October in its native range....
occur only on East Wallabi Island.
As of 2001, 5 species of priority flora occurred on the islands. One,
Acacia didymaAcacia didyma is a shrub or small tree which is native to Western Australia. It grows to between 1.5 metres and 4 metres in height and flowers from August to October in its native range....
, is no longer considered a priority species. The remaining priority species are
Chthonocephalus tomentellusChthonocephalus tomentellus is an annual herb in the family Asteraceae. It is endemic to Western Australia, occurring in saline depressions...
, which is rated Priority Two under the Department of Environment and Conservation's Declared Rare and Priority Flora List;
Calocephalus aervoidesCalocephalus aervoides is a herb in the family Asteraceae. It produces yellow flowers from September to October in its native range....
and
Galium migransGalium migrans is a species of flowering plant in the family Rubiaceae. It is native to in the Australian states of Western Australia, South Australia, Victoria, New South Wales and Queensland....
, both Priority Three; and
Lepidium puberulumLepidium puberulum is an annual herb in the Brassicaceae family, endemic to the west coast of Western Australia. The species has white or green flowers that appear from July to November in its native range.-References:...
, Priority Four.
95 exotic species from 29 families have been recorded. In general, islands that have or had human settlements are the weediest. Of greatest concern is the noxious weed
Lycium ferocissimumLycium ferocissimum is a shrub in the nightshade family . The species is native to Cape Province and Orange Free State in South Africa and has become naturalised in Australia and New Zealand. It is listed on the Noxious Weed List for Australian States and Territories and is a declared noxious weed...
(African Boxthorn), which has long spines that can trap birds. This weed was recorded on the islands as early as 1970. Efforts to eradicate it began in 1990,; there was a lull in eradication in the late 1990s, but the program was later reinstated, and in July 2007, the Department of Environment and Conservation reported that the species had been eradicated from 14 of the 18 islands on which it had been recorded. Other noxious weeds include
Opuntia strictaOpuntia stricta, commonly known known as Erect Prickly Pear, is a species of cactus from southern North America and Central America....
(Prickly Pear),
Verbesina encelioidesVerbesina encelioides is a flowering plant in the family Asteraceae. The species is native to the United States and Mexico and naturalized elsewhere....
and
Echium plantagineum (Paterson's Curse).
Birds
The Houtman Abrolhos is home to around 100 species of bird; for a complete list, see
list of birds of the Houtman Abrolhos. Six species are land birds, and three are shore birds. The remainder, the vast majority, are
seabirdSeabirds are birds that have adapted to life within the marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same environmental problems and feeding niches have resulted in similar adaptations...
s. Most seabird species have a tropical distribution, but some occur in both tropical and warm-temperate seas, and a small number are warm-temperate only.
When numbers of individuals are taken into account, the tropical birds overwhelmingly dominate. The islands are one of the most important breeding sites for tropical seabirds in Australia. They contain by far the largest colonies of
Wedge-tailed ShearwaterThe Wedge-tailed Shearwater, Puffinus pacificus is a medium-large shearwater in the seabird family Procellariidae. It is one of the shearwater species that is sometimes referred to as a Muttonbird, like the Sooty Shearwater of New Zealand and the Short-tailed Shearwater of Australia...
in the eastern Indian Ocean, with over a million breeding pairs recorded there in 1994. They also contain Western Australia's only breeding colonies of the
Lesser NoddyThe Lesser Noddy is a species of tern in the Sternidae family.It is found in Comoros, Kenya, Liberia, Mauritius, Seychelles, South Africa, and United Arab Emirates.-References:...
, and the largest colonies in Western Australia of the
Little ShearwaterThe Little Shearwater , sometimes called Southern Little Shearwater to distinguish it from the North Atlantic Little Shearwater which was formerly included in this species, is a small shearwater in the seabird family Procellariidae.It nowadays contains 5 accepted subspecies, with mtDNA cytochrome b...
, White-faced Storm Petrel, Common Noddy,
Caspian TernThe Caspian Tern is a species of tern, with a subcosmopolitan but scattered distribution. Despite its extensive range, it is monotypic, with no subspecies accepted...
, Crested Tern,
Roseate TernThe Roseate Tern is a seabird of the tern family Sternidae. This bird has a number of geographical races, differing mainly in bill colour and minor plumage details....
and
Fairy TernThe Fairy Tern is a small tern which occurs in the southwestern Pacific.There are three subspecies:* Australian Fairy Tern, Sterna nereis nereis - breeds in Australia...
. In addition, they contain important breeding areas for the Eastern Reef Heron,
Pacific GullThe Pacific Gull is a very large gull, native to the coasts of Australia. It is moderately common between Carnarvon in the west, and Sydney in the east, although it has become scarce in some parts of the south-east, as a result of competition from the Kelp Gull, which has "self-introduced" since...
,
Bridled TernThe Bridled Tern is a seabird of the tern family Sternidae. It is a bird of the tropical oceans...
,
White-bellied Sea EagleThe White-bellied Sea-eagle , also known as the White-bellied Fish-eagle or White-breasted Sea Eagle, is a large diurnal bird of prey in the family Accipitridae. It is closely related to other eagles, kites, hawks, harriers and Old World vultures.It is resident from India through southeast Asia to...
and
OspreyThe Osprey , sometimes known as the sea hawk, is a diurnal, fish-eating bird of prey. It is a large raptor, reaching 60 centimetres in length with a 1.8 metre wingspan...
.
There are two subspecies of bird endemic to the islands. The
Abrolhos Painted Button-quailThe Abrolhos Painted Button-quail is a subspecies of the Painted Buttonquail endemic to the Houtman Abrolhos. It is common on North Island, and also occurs on other islands of the Wallabi Group, namely East Wallabi, West Wallabi, Seagull and Pigeon Islands...
occurs only on five islands in the Wallabi Group, and is protected as rare under the
Wildlife Conservation Act 1950The Wildlife Conservation Act 1950 is an act of the Western Australian Parliament that provides the statute relating to conservation and legal protection of flora and fauna....
. Also gazetted as rare, the Australasian subspecies of the Lesser Noddy,
Anous tenuirostris melanops, breeds only on Wooded Island, Morley Island and Pelsaert Island.
Mammals
Only two species of land mammal are indigenous to the Houtman Abrolhos, the
Tammar WallabyThe Tammar Wallaby , also known as the Dama Wallaby or Darma Wallaby, is a small member of the kangaroo family and is the type species for research on kangaroos and marsupials....
(
Macropus eugenii) and the
Bush RatThe Bush Rat is a small Australian nocturnal animal. It is an omnivore.It is one of the most common species of rats and is found in many heathland areas of Victoria and NSW...
(
Rattus fuscipes). Both are native only to West and East Wallabi Islands, although
R. fuscipes has not been collected on East Wallabi Island since August 1967, and is probably extinct there. The Tammar Wallabi was seen on West Wallabi Island by survivors of the 1628
Batavia shipwreck, and recorded by Francisco Pelsart in his 1629
Ongeluckige Voyagie. This represents the first recorded sighting of a
macropodMacropods are marsupials belonging to the family Macropodidae, which includes kangaroos, wallabies, tree-kangaroos, pademelons, and several others. Before European settlement, there were about 53 species of Macropods. Six species have since become extinct. Another 11 species have been greatly...
by Europeans, and probably also the first sighting of an Australian mammal. Tammar Wallabies were introduced to North Island from East Wallabi Island by fishermen, probably in the 1950s, but failed to establish. In 1987 they were reintroduced again, this time successfully. By the 2000s, there were over 400 wallabies on the island, resulting in overgrazing of native vegetation and increased
erosionErosion is a gravity driven process that moves solids in the natural environment or their source and deposits them elsewhere...
. Research into the effectiveness of controlling population levels by the use of implanted contraceptives was begun in 2005, but in July 2007 the research was discontinued and the population culled instead.
Two introduced mammals are established on the islands. The Domestic Cat (
Felis silvestris catus) was introduced to Rat Island around 1900, and the
House MouseThe House Mouse is one of the most numerous species of the genus Mus commonly termed a mouse. It is a small mammal and a rodent....
(
Mus musculus) was introduced onto North Island in the 1970s, presumably with food. In 1995 the House Mouse was reported as also present on Rat Island for many years before 1987, but a recent report makes no mention of this. In addition, three introduced mammals were previously established in the Houtman Abrolhos, but have since been eradicated. The
Black RatThe Black Rat is a common long-tailed rodent of the genus Rattus in the subfamily Murinae...
(
Rattus rattus) was established on Pigeon and Rat Islands, but has been eradicated by poisoning. The
European RabbitThe European Rabbit is a species of rabbit native to south west Europe . It has been widely introduced elsewhere often with devastating effects on local biodiversity...
(
Oryctolagus cuniculus) has been introduced at various times onto Leo Island, Middle Island, Morley Island, Pelsaert Island and Wooded Island. In the case of Pelsaert Island, it is not clear whether it ever established; in all other cases, established populations have been eradicated by poisoning. The Domestic Goat (
Capra aegagrus hircus) is also reported to have been present on East Wallabi Island, but is no longer.
Reptiles
23 terrestrial reptile species are known to occur on the islands of the Houtman Abrolhos. This relatively low biodiversity is apparently due to the homogeneity of habitat on the islands, which provide few distinct
ecological nicheIn ecology, a niche is a term describing the relational position of a species or population in its ecosystem to each other; e.g. a dolphin could potentially be in another ecological niche from one that travels in a different school if the members of these schools utilize significantly different...
s. The most significant terrestrial reptile species are the Spiny-tailed Skink (
Egernia stokesii stokesii) and the Carpet Python (
Morelia spilota imbricataMorelia spilota imbricata is a large snake found in southern regions of Western Australia. A member of the python family, it is commonly known as the Southern Carpet Python.-Description:...
), both of which are listed as rare and therefore afforded special protection under the
Wildlife Conservation Act 1950The Wildlife Conservation Act 1950 is an act of the Western Australian Parliament that provides the statute relating to conservation and legal protection of flora and fauna....
; and the Abrolhos Dwarf Bearded Dragon (
Pogona minor minimaPogona minor minima is an agamid lizard found only on islands at Houtman Abrolhos, and commonly named for this location; the Abrolhos Bearded Dragon. It is closely related to other Bearded dragons found in Western Australia....
), a Houtman Abrolhos endemic that is listed as a Priority 4 species by the Department of Environment and Conservation. For a full list of species, see
list of reptiles of the Houtman Abrolhos.
Amphibians
Specimens of the Pobblebonk (
Limnodynastes dorsalisLimnodynastes dorsalis is a frog species from the family Myobatrachidae. The informal names for this species are Western Banjo Frog, Pobblebonk, Sand frog and Bullfrog. It is one of the endemic amphibians of Western Australia....
) and the Turtle Frog (
Myobatrachus gouldii) were collected from the Houtman Abrolhos during the Percy Sladen Trust Expedition of 1913 and 1915, but no amphibians have been recorded on the islands since that time.
Algae
260 species of benthic
algaeAlgae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms. The largest and most complex marine forms are called seaweeds. They are photosynthetic, like plants, and "simple" because they lack the many distinct organs found in...
have been recorded at the Houtman Abrolhos. This figure comprises 178 species of
red algaeThe red algae are one of the oldest groups of eukaryotic algae, and also one of the largest, with about 5,000–6,000 species of mostly multicellular, marine algae, including many notable seaweeds...
(Rhodophyta), 50 species of
brown algaeThe Phaeophyceae or brown algae, is a large group of mostly marine multicellular algae, including many seaweeds of colder Northern Hemisphere waters. They play an important role in marine environments both as food, and for the habitats they form...
(Phaeophyta) and 32 species of
green algaeThe green algae are the large group of algae from which the embryophytes emerged. As such, they form a paraphyletic group, although the group including both green algae and embryophytes is monophyletic...
(Chlorophyta). Both temperate and tropical species are present, in many cases near the northern or southern extent of their range. For a full list, see
list of algae of the Houtman Abrolhos.
Seagrass
Only ten species of seagrass have been recorded at the Houtman Abrolhos. Seven of these are temperate species at or near the northern limit of their range; the other three have a tropical distribution. That there are so few tropical species may be due to periods of low sea temperatures, or the small areas of suitable habitat at the Abrolhos; alternatively it may be that more collecting effort is needed in habitats that suit tropical species. The seagrass species recorded at the Houtman Abrolhos islands are:
- Amphibolis antarctica
Amphibolis antarctica, commonly known as Wire weed or Sea Nymph, is a seagrass found in coastal waters of southern and western Australia.-Description:...
- Amphibolis griffithii
Amphibolis griffithii is a seagrass found in waters along the southwestern coasts of Western Australia. -Description:A common marine herb, the rhizomatous plant forms meadows which stabilise sands; the intertwining roots and leaves protects the substrate from ocean currents...
- Halophila decipiens
- Halophila ovalis
Halophila ovalis is a seagrass in the family Hydrocharitaceae, a common name is paddle weed. It is a small herbaceous plant that occurs in sea beds and other saltwater environments....
|
Posidonia angustifolia
Posidonia australis Posidonia australis is a species of seagrass that occurs in the southern waters of Australia. It is sometimes referred to as Fibreball Weed. The marine plant forms large meadows that are considered to be of high importance to the environmental conservation of the region...
Posidonia coriaceaPosidonia coriacea is a species of seagrass that occurs in the southern waters of Australia.-Description:A species of Posidonia. A perennial rhizomatous herb that appears as stands in marine habitat. This species is found at depths from 1 to 30 metres on white sands, in areas subject to intense...
|
Posidonia sinuosa
Syringodium isoetifolium
Thalassodendron pachyrhizum |
Fish
At last count, a total of 389 species of fish have been recorded from the Houtman Abrolhos. 16 species occur in very large numbers; in decreasing order of abundance, these are:
- Pomacentrus milleri (Miller's Damsel)
- Scarus schlegeli (Schlegel's Parrotfish)
- Stethojulis strigiventer (Stripebelly Wrasse)
- Coris auricularis (Western King Wrasse)
- Kyphosus cornelii (Western Buffalo Bream)
- Choerodon rubescens (Baldchin Groper)
- Chromis westaustralis (West Australian Puller)
- Thalassoma lutescens
Thalassoma lutescens is a Wrasse from the Indo-Pacific. It occasionally makes its way into the aquarium trade. It grows to a size of 30 cm in length....
(Green Moon Wrasse)
- Scarus ghobban (Blue-barred Orange Parrotfish)
- Abudefduf sexfasciatus (Scissortail Sergeant)
- Thalassoma lunare (Moon Wrasse)
- Stegastes obreptus (Western Gregory)
- Halichoeres brownfieldi (Brownfield's Wrasse)
- Amblygobius phalaena
Amblygobius phalaena is a Goby from the Pacific Ocean. It occasionally makes its way into the aquarium trade. It grows to a size of 15 cm in length....
(White-barred Goby)
- Asterropteryx semipunctatus (Starry Goby)
- Anampses geographicus (Scribbled Wrasse)
Commercially important species include
Pagrus auratus (Pink Snapper),
Choerodon rubescens (Baldchin Groper),
Glaucosoma hebraicumGlaucosoma hebraicum is a species of fish, informally known as the West Australian dhufish. The local name for the species is jewfish or pearl perch, and regarded as good eating. The distribution is from Shark Bay, Western Australia to the Archipelago of the Recherche.The pearlescent, silver-grey,...
(Westralian Dhufish) and
Plectropomus leopardus (Coral Trout). For a complete list of fish species recorded at the Houtman Abrolhos, see
list of fishes of the Houtman Abrolhos.
About two thirds of the total number of species are tropical in distribution, the remainder being subtropical or warm-temperate. This ratio also holds for the most abundant species, eleven of the sixteen species being tropical. On the other hand, over 70% of tropical species occur in extremely low numbers, so low in fact that they are thought not to maintain breeding populations at the Abrolhos; rather, populations are maintained by
larvaA larva is a young form of animal with indirect development, going through or undergoing metamorphosis ....
e carried to the islands by the Leeuwin Current from populations further north.
Marine mammals
The Houtman Abrolhos maintains a breeding population of
Australian Sea LionThe Australian Sea Lion is a species of sea lion that breeds only on the south and west coasts of Australia. Today there are about 10,000 Australian Sea Lions following the introduction of the Australian National Parks and Wildlife Act of 1972 which prohibited a harvest that began in earnest as...
s (
Neophoca cinerea), probably numbering between 75 and 100. Historical data suggests numbers were previously much higher; for example, in 1727 survivors of the
Zeewyk shipwreck killed over 150 sea lions in the Southern Group alone. This has led to a 1727 population estimate of between 290 and 580 animals for the entire Houtman Abrolhos. Populations apparently fell dramatically between the 1840s and the 1880s, largely due to extensive commercial
sealingSeal hunting, or sealing, is the personal or commercial hunting of seals. The hunt is practiced in five countries: Canada, where most of the world's seal hunting takes place, as well as Namibia, Greenland, Norway, and Russia...
in the area. In addition to direct killing of the animals, it is likely that much of the
mangroveMangroves are trees and shrubs that grow in saline coastal habitats in the tropics and subtropics – mainly between latitudes N and S. The saline conditions tolerated by various species range from brackish water, through pure seawater , to water of over twice the salinity of ocean seawater,...
habitat on the islands was cleared as fuel for trypots, and this may have affected the survival of young pups. Populations are thought to have been fairly stable for the last fifty years, although the lack of genetic diversity in the smaller population remains of concern, as does
climate changeClimate change is a change in the statistical distribution of weather over periods of time that range from decades to millions of years. It can be a change in the average weather or a change in the distribution of weather events around an average...
.
Sea lions come ashore to rest on leeward beaches throughout the island chain, but only a small number of these "haulout sites" are used for breeding. Breeding has been observed on Serventy Island, Gilbert Island,
Alexander IslandAlexander Island is one of the five largest islands in the Easter Group of the Houtman Abrolhos. It is nominally located at...
, Suomi Island, Keru Island, Square Island, Stick Island,
Gibson IslandGibson Island may refer to:In the United States:* Gibson Island * Gibson Islands In other locations:* Gibson Island * Gibson Island...
,
Gun IslandGun Island is one of the larger islands in the Pelsaert Group of the Houtman Abrolhos. It is nominally located at , about 4 km north and east of Half Moon Reef and is a flat limestone outcrop of about by in size....
, Morley Island and Wooded Island. All but the last three of these are considered current breeding sites, and are therefore considered by the Department of Fisheries to have a high conservation value.
Little information is available on other marine mammals at the Abrolhos, as no direct research on this subject has been undertaken. Sightings of the
Humpback WhaleThe humpback whale is a baleen whale. One of the larger rorqual species, adults range in length from and weigh approximately . The humpback has a distinctive body shape, with unusually long pectoral fins and a knobbly head. It is an acrobatic animal, often breaching and slapping the water...
(
Megaptera novaeangliae) are common between April and October, when the whales are migrating. Other marine mammals sometimes sighted at the islands include Pygmy Bryde's Whale (
Balaenoptera edeni),
Bottlenose DolphinBottlenose dolphins, the genus Tursiops, are the most common and well-known members of the family Delphinidae, the family of oceanic dolphins. Recent molecular studies show the genus contains two species, the Common Bottlenose Dolphin and the Indo-Pacific Bottlenose Dolphin , where previous...
(
Tursiops aduncus) and
Striped DolphinThe Striped Dolphin is an extensively studied dolphin that is found in temperate and tropical waters of all the world's oceans.-Taxonomy:...
(
Stenella coeruleoalba).
Marine reptiles
The Green Turtle (
Chelonia mydas) and the Loggerhead Turtle (
Caretta caretta) both live in the waters off the Houtman Abrolhos, albeit in low numbers. Neither species breeds in the area, as water temperatures are too low.
Coral
The Houtman Abrolhos is unusual in having a luxuriant and diverse living coral reef at such a high latitude. 194 species in 50 genera have been recorded there, all but two of which are tropical. This is a surprisingly high coral diversity, considering the high latitude of the reef, and the relatively low diversity of other biota. For a full list, see
list of corals of the Houtman Abrolhos.
The coral reef community at the Houtman Abrolhos is unusual in having tropical coral growing alongside and in direct competition with, temperate
seaweedSeaweedSeaweed has antioxidents. Is a loose colloquial term encompassing macroscopic, multicellular, benthic marine algae. The term includes some members of the red, brown and green algae...
. As a result of this competition for light, space and nutrients, coral at the Houtman Abrolhos tends to grow more slowly and die younger than is usual. Reef production is to a large extent due to the production of carbon by
coralline algaeCoralline algae are red algae in the Family Corallinaceae of the order Corallinales. They are characterized by a thallus that is hard because of calcareous deposits contained within the cell walls...
rather than by coral.
Crustaceans
The most notable species of
crustaceanCrustaceans are a very large group of arthropods, comprising almost 52,000 described species , and are usually treated as a subphylum . They include various familiar animals, such as crabs, lobsters, crayfish, shrimp, krill and barnacles...
at the Houtman Abrolhos is the
Western Rock LobsterPanulirus cygnus is a species of spiny lobster , found off the west coast of Australia. Panulirus cygnus is the basis of Australia's most valuable fishery, making up 20% of value of Australia's total fishing industry, and is identified as the western rock lobster.The species has five pairs of legs...
(
Panulirus cygnus). 44 species of
crabCrabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax.Crabs have a soft body covered with a hard shell. They are generally covered with a thick exoskeleton, and armed with a...
and 9 species of amphipod were recorded there by the Percy Sladen Trust Expedition of 1916.
Molluscs
492 species of marine mollusc have been recorded from the shallow waters of the Houtman Abrolhos. These are predominantly gastropods (346 species, 70%) and bivalves (124, 25%); the remaining 5% of species consist of
cephalopod{Taxobox| name = Cephalopods| fossil_range = | image = Tafel 054 300.jpg| image_caption = A variety of cephalopod forms from Ernst Haeckel's 1904 Kunstformen der Natur| regnum = Animalia| image_width = 220px| phylum = Mollusca| classis = Cephalopoda...
s (14 species),
chitonChitons are small to large, primitive marine molluscs in the class Polyplacophora.There are 900 to 1,000 extant species of chitons in the class, which was formerly known as Amphineura....
s (5 species) and scaphopods (3 species). About two thirds of the species have a tropical distribution, temperate species account for 20%, and the remaining 11% are endemic to Western Australia. For a full list, see
List of molluscs of the Houtman Abrolhos.
The Southern Saucer Scallop (
Amusium balloti) is the only commercially important species. This occurs in sheltered areas of medium-fine sand in deep water to the north-east of the reefs; it is usually the dominant species there.
Echinoderms
Houtman Abrolhos has an extremely high diversity of echinoderms, with 172 species having been recorded there. 63% of these are tropical species, 14% are temperate, and 22% are endemic to Western Australia. None is endemic to the Houtman Abrolhos. Published surveys have not included observations of the
crown-of-thorns starfishThe Crown-of-Thorns Starfish is a large nocturnal sea star that preys upon coral polyps. The Crown-of-Thorns receives its name from venomous thorn-like spines that cover its body....
(
Ananthaster planci), but individuals have occasionally been observed there. For a complete list of species, see
list of echinoderms of the Houtman Abrolhos.
Other invertebrates
The sponges of the Houtman Abrolhos are poorly studied, although 109 species of
demospongeThe Demospongiae are the largest class in the phylum Porifera. Their "skeletons" are made of spicules consisting of fibers of the protein spongin, the mineral silica, or both. They contain 90% of all species of sponges and are predominantly leuconoid structural grade.There are many diverse orders...
have been collected there. In the most recent survey, 77 species were collected, of which around half are probably new to science. Only two locations were surveyed in this study, however, so this figure is likely to represent only a small proportion of the total sponge fauna of the Houtman Abrolhos; the islands are therefore thought to harbour an extremely rich diversity of sponges. A preliminary assessment suggested that there were more temperate species than tropical, which stands in marked contrast to most other groups.
The
marine wormAny worm that lives in a marine environment is considered a marine worm. Marine worms are found in several different phyla, including the Platyhelminthes, Nematoda, Annelida, Chaetognatha, Hemichordata, etc....
s identified at the Houtman Abrolhos include 22 species of the
polychaeteThe Polychaeta or polychaetes are a class of annelid worms, generally marine. Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are made of chitin. Indeed, polychaetes are sometimes referred to as bristle worms. More than 10,000...
family
TerebellidaeTerebellidae is a family of polychaete worms. They are surface deposit feeders, catching falling particles with numerous elongate prostomial tentacles splayed out on the sea floor. These tentacles, which are the most or only normally visible portion of the animal and are reminiscent of spaghetti,...
, and 16 species of the family oligochaete family
TubificidaeThe Naididae are a family of clitellate oligochaete worms like the sludge worm, Tubifex tubifex. They are key components of the benthic communities of many freshwater and marine ecosystems....
. For a list of species, see
list of worms of the Houtman Abrolhos.
A total of 38
hydroid-Marine Biology:Colonial, plant-like animals closely related to jellyfish, with stinging cellsany member of the invertebrate order Hydroida...
species have been collected at the Houtman Abrolhos. 34 of these are leptothecates, the remainder being anthoathecates. 92% of the species attach to temperate algae, the others to coral rubble. For a list of species, see
list of hydroids of the Houtman Abrolhos.
Western rock lobster
It is the centre of the
Western Rock LobsterPanulirus cygnus is a species of spiny lobster , found off the west coast of Australia. Panulirus cygnus is the basis of Australia's most valuable fishery, making up 20% of value of Australia's total fishing industry, and is identified as the western rock lobster.The species has five pairs of legs...
fishery, the largest single-species fishery in Western Australia.
Saucer scallops
After Shark Bay, the Houtman Abrolhos supports Western Australia's second largest saucer scallop fishery. This fishery is managed under the
Abrolhos Islands and Mid West Trawl Limited Entry Fishery Notice 1993. Only 17 licences have been issued, and no more will be made available, as the saucer scallop is considered fully exploited. Licensees are constrained to operate only during scallop season, which generally runs from 1 April to 30 June, and are also subject to restrictions on gear design, boat size and crew numbers.
Scallop fishers mainly operate east of the Houtman Abrolhos and between the island groups, in waters deeper than 30 metres. Activity is targeted at sheltered areas of bare sand, where scallops tend to settle. Catches vary greatly from year to year; from 2001 to 2003, for example, the total annual catch totalled 1182 tons, 195 tons and 5840 tons (whole weight) respectively. This variability is apparently related to the strength of the Leeuwin Current, as strong current is correlated with low scallop recruitment.
The total value of the fishery in 2003 was AU$19.6 million, although this figure includes a small prawn fishery operating out of Port Gregory. Most of the catch is frozen and exported to Asia.
Aquaculture
The Department of Fisheries have issued a number of licences to cultivate black-lip pearl oysters in the Abrolhos. The first recipient of a license was Abrolhos Pearls in 1996. By 2000, another license had been issued and four more applications had been received. A year later, there were 10 square kilometres licensed for the culture of pearl oysters in the Abrolhos, of which about 21% was actually in use, carrying over 210,000 shell. Six licences had been issued by 2002, and by 2007 that number had grown to eight.
95% of the
pearlA pearl is a hard, generally spherical object produced within the soft tissue of a living shelled mollusk. Just like the shell of a mollusk, a pearl is made up of calcium carbonate in minute crystalline form, which has been deposited in concentric layers. The ideal pearl is perfectly round and...
aquacultureAquaculture is the farming of freshwater and saltwater organisms such as finfish, molluscs, crustaceans and aquatic plants. Also known as aquafarming, aquaculture involves cultivating aquatic populations under controlled conditions, and can be contrasted with commercial fishing, which is the...
is carried out in the Pelsaert Group. Most licenses are over areas of sand, but some areas contain small amounts of coral reef. The colour of the pearls produced is quite different to that of Pacific black pearls, and this is considered a potential marketing tool.
In addition to pearl aquaculture, a pilot sea cage finfish farm was licensed in 2004, although as of 2007 the license had not been exercised. Interest has also been expressed in the culture of
live rock"Live rock" is rock from the ocean that has been introduced into a saltwater aquarium, which confers to the closed marine system multiple benefits desired by the salt water aquarium hobbyist...
and coral for the
aquariumAn aquarium is a vivarium consisting of at least one transparent side in which water-dwelling plants or animals are kept. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, marine mammals, turtles, and aquatic plants...
industry. The Department of Fisheries has identified a number of species as having potential for aquaculture in the Abrolhos, including the Shark Bay pearl oyster (
Pinctada albina-Pinctada:Pinctada is a genus of pearl oysters. These are saltwater clams, marine bivalve mollusks of the genus Pinctada in the family Pteriidae. They have a strong inner shell layer composed of nacre, also known as mother of pearl...
), the
maxima clamThe maxima clam , also known as the small giant clam, is a species of clam found throughout the Indo-Pacific. They are much sought after in the aquarium trade, as their often striking coloration mimics that of the true giant clam, however the maximas maintain a manageable size, with the shells of...
(
Tridacna maxima),
rock oysterRock oysters are true oysters of the genus Saccostrea. The best known species of rock oyster is the Sydney rock oyster .- Species :* Saccostrea...
s (
Saccostrea sp.), the saucer scallop (
Amusium balloti), the western rock lobster, and a number of species of finfish, most of which are
filter feederFilter feeders are animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feeding are clams, krill, sponges, some fish and sharks, and baleen whales. Some birds, such...
s.
Mineral exploration
Petroleum explorationHydrocarbon exploration is the search by petroleum geologists and geophysicists for hydrocarbon deposits beneath the Earth's surface, such as oil and natural gas...
wells were drilled in Abrolhos waters in the 1960s and 1970s, but were capped and abandoned. The Abrolhos was amongst the areas released for further exploration in 2002.
Recreation
The Abrolhos provides some of the best
snorkelingSnorkeling is the practice of swimming on or through a body of water while equipped with a diving mask, a shaped tube called a snorkel, and usually swimfins. In cooler waters, a wetsuit may also be worn...
,
divingDiving is the sport of jumping or falling into water from a platform or springboard, sometimes while performing acrobatics. Diving is an internationally-recognized sport that is part of the Olympic Games. In addition, unstructured and non-competitive diving is a recreational pastime.Diving is one...
and deep sea fishing in the world, along with some of Australia's most significant historical sights, such as the
shipwreckA shipwreck is the remains of a ship that has wrecked, it having either been sunk or beached. A shipwreck can refer to a wrecked ship or to the event that caused the wreck, such as the striking of something that causes the ship to sink, the stranding of the ship on rocks, land or shoal, or the...
of the
BataviaBatavia was a ship of the Dutch East India Company . She was built in Amsterdam in 1628, and had 24 cast-iron cannons. Batavia was shipwrecked on her maiden voyage, and made famous by the subsequent mutiny and massacre that took place among the survivors...
.
Nowadays, many of the islets are used by fishermen. Although an important tourist destination, the tourists are not allowed to stay overnight.
Cultural references
The majority of cultural references to the Houtman Abrolhos relate to the islands' shipwrecks, particularly the
Batavia. The events surrounding the loss of the
Batavia is one of the most celebrated episodes in Australian popular history; in the words of Henrietta Drake-Brockman:The story has spawn a massive body of literature, both fiction and non-fiction, as well as numerous works in other media.
Other shipwrecks, notably the
Zeewijk, have also become the subject of books and other works. Shipwrecks aside, however, cultural references to the Houtman Abrolhos are rare. By far the best known book on the Houtman Abrolhos itself is
Malcolm UrenMalcolm Uren journalist and editor of the Western Mail.e-Early life:Uren was born on 7 January 1900 in West Hindmarsh, Adelaide, South Australia to Malcolm Francis Uren and Millicent Jane Leggoe. The Uren family moved to Perth, WA. Malcolm married Lenora Emily Olive Klenk on 25 August 1923...
's
Sailormen's ghosts: The Abrolhos islands in three hundred years of romance, history, and adventure. First published in 1940, this book saw numerous editions published in the 1940s, and was even republished in 1980 as a "West Australian classic". In it, Uren tells both the history of the islands and the story of his own visit to the islands.
Other books include William Bede Christie's 1909
Christmas on the briny: the innocents abroad, or, a holiday trip to the Abrolhos islands, and Alison Louise Wright's 1998
Abrolhos Islands Conversations. The latter, a book of interviews and portraits of the people of the Abrolhos, won the Special Award in the 1999
Western Australian Premier's Book AwardsThe Western Australian Premier's Book Awards is an award for books and scripts written by Western Australians or about Western Australia. Awards are provided by the Government of Western Australia, and the awards process is managed by the State Library of Western Australia...
.
The islands featured in the first episode of
Surfing the Menu, an eight-part food and travel series produced for the
ABCThe Australian Broadcasting Corporation, commonly referred to as "the ABC", is Australia's national public broadcaster. With a total budget of AUD$1.13 Billion annually, the corporation provides television, radio, online and mobile services throughout metropolitan and regional Australia, as well as...
in 2003., and the following year were featured on
GetawayGetaway is Australia's longest-running and most popular holiday and travel television programme. Debuting on 14 May 1992, it is currently broadcast on the Nine Network and W...
, Australia's longest-running and most popular holiday and travel television programme. They were the subject of a motion picture entitled
Eye opener, published by The Film Centre WA in 1981, and of a piece of classical music entitled
Abrolhos: A ceremonial overture, written by William Stewart in 1988 under commission to the Geraldton Town Council.
Further reading
- Collins, Lindsay. (1991) The Abrolhos coral reefs – history and present management. Curtin gazette, Mar 1991, p. 5–11
- Myra Stanbury et al. (2000) Abrolhos Islands archaeological sites : interim report, Fremantle, W.A. Australian National Centre of Excellence for Maritime Archaeology. Special publication no. 5. ISBN 1-876465-12-3