A
harmful algal bloom (HAB) is an
algal bloomAn algal bloom is a rapid increase in the population of algae in an aquatic system. Algal blooms may occur in freshwater as well as marine environments. Typically, only one or a small number of phytoplankton species are involved, and some blooms may be recognized by discoloration of the water...
— a dense aggregation of
phytoplanktonPhytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words φυτον , or "plant", and πλαγκτος , meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye...
,
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...
or
cyanobacteriaCyanobacteria, also known as blue-green algae, blue-green bacteria or Cyanophyta, is a phylum of bacteria that obtain their energy through photosynthesis. The name "cyanobacteria" comes from the color of the bacteria = blue)...
in a marine or aquatic environment — that causes negative impacts to other organisms via production of natural toxins, mechanical damage to other organisms, or by other means. HABs are often associated with large-scale marine mortality events and have been associated with various types of shellfish poisonings.
In the marine environment, single-celled, microscopic, plant-like organisms naturally occur in the well-lit surface layer of any body of water.
A
harmful algal bloom (HAB) is an
algal bloomAn algal bloom is a rapid increase in the population of algae in an aquatic system. Algal blooms may occur in freshwater as well as marine environments. Typically, only one or a small number of phytoplankton species are involved, and some blooms may be recognized by discoloration of the water...
— a dense aggregation of
phytoplanktonPhytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words φυτον , or "plant", and πλαγκτος , meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye...
,
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...
or
cyanobacteriaCyanobacteria, also known as blue-green algae, blue-green bacteria or Cyanophyta, is a phylum of bacteria that obtain their energy through photosynthesis. The name "cyanobacteria" comes from the color of the bacteria = blue)...
in a marine or aquatic environment — that causes negative impacts to other organisms via production of natural toxins, mechanical damage to other organisms, or by other means. HABs are often associated with large-scale marine mortality events and have been associated with various types of shellfish poisonings.
Background
In the marine environment, single-celled, microscopic, plant-like organisms naturally occur in the well-lit surface layer of any body of water. These organisms, referred to as
phytoplanktonPhytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words φυτον , or "plant", and πλαγκτος , meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye...
or microalgae, form the base of the food web upon which nearly all other marine organisms depend. Of the 5000+ species of marine phytoplankton that exist worldwide, about 2% are known to be harmful or toxic. When populations of one phytoplankton species out-compete other co-occurring species in the water, they can dominate the phytoplankton community and are said to "bloom". Blooms of harmful algae can have large and varied impacts on marine ecosystems, depending on the species involved, the environment where they are found, and the mechanism by which they exert negative effects. Examples of common harmful effects of HABs include:
- human illness via consumption of seafood contaminated by HABs
- the production of neurotoxins which cause mass mortalities in fish, seabirds and marine mammals
- mechanical damage to other organisms, such as disruption of epithelial gill tissues in fish, resulting in asphyxiation
- oxygen depletion of the water column from cellular respiration and bacterial degradation
HABs occur in many regions of the world, and in the United States are recurring phenomena in multiple geographical regions. The Gulf of Maine frequently experiences blooms of the
dinoflagellateThe dinoflagellates are a large group of flagellate protists. Most are marine plankton, but they are common in fresh water habitats as well. Their populations are distributed depending on temperature, salinity, or depth. About half of all dinoflagellates are photosynthetic, and these make up the...
Alexandrium, an organism that produces
saxitoxinSaxitoxin is a neurotoxin naturally produced by certain species of marine dinoflagellates and cyanobacteria Saxitoxin (STX) is a neurotoxin naturally produced by certain species of marine dinoflagellates (Alexandrium sp., Gymnodinium sp., Pyrodinium sp.) and cyanobacteria Saxitoxin (STX) is a...
, the neurotoxin responsible for
paralytic shellfish poisoningParalytic shellfish poisoning is one of the four recognized syndromes of shellfish poisoning . All four syndromes share some common features and are primarily associated with bivalve molluscs...
. The well-known "Florida red tide" that occurs in the eastern Gulf of Mexico is a HAB caused by
Karenia brevis- Description :Karenia brevis is a marine dinoflagellate common in Gulf of Mexico waters, and is the organism responsible for Florida red tide, as well as red tide in Texas. K...
, another
dinoflagellateThe dinoflagellates are a large group of flagellate protists. Most are marine plankton, but they are common in fresh water habitats as well. Their populations are distributed depending on temperature, salinity, or depth. About half of all dinoflagellates are photosynthetic, and these make up the...
which produces
brevetoxinBrevetoxin , or brevetoxins, are a suite of cyclic polyether compounds produced naturally by a species of dinoflagellate known as Karenia brevis...
, the neurotoxin responsible for
neurotoxic shellfish poisoningNeurotoxic Shellfish Poisoning is caused by the consumption of shellfish contaminated by brevetoxins or brevetoxin analogs.Symptoms in humans include vomitting and nausea and a variety of neurologic symptoms such as slurred speech. No fatalities have been reported but there are a number of cases...
. California coastal waters also experience seasonal blooms of
Pseudo-nitzschia, a
diatomDiatoms are a major group of eukaryotic algae, and are one of the most common types of phytoplankton. Most diatoms are unicellular, although they can exist as colonies in the shape of filaments or ribbons Diatoms (Greek: (dia) = "through" + (temnein) = "to cut", i.e., "cut in half") are a major...
known to produce
domoic acidDomoic acid , the neurotoxin which causes amnesic shellfish poisoning , is an amino acid associated with certain harmful algal blooms.-Occurrence:...
, the neurotoxin responsible for
amnesic shellfish poisoningAmnesic shellfish poisoning is a human illness caused by consumption of the marine biotoxin called domoic acid. This toxin is produced naturally by marine diatoms belonging to the genus Pseudo-nitzschia and, when accumulated in high concentrations by shellfish, can then be passed on to humans via...
.
"Red Tide"
Although the term "
red tideRed tide is a common name for a phenomenon more correctly known as an algal bloom , an event in which estuarine, marine, or fresh water algae accumulate rapidly in the water column and results in discoloration of the surface water...
" is often used to describe these and similar phenomena, the more correct and preferred term in use is harmful algal bloom, because:
- not all algal blooms are harmful
- not all algal blooms cause discoloration of water
- these blooms are not associated with tides
Causes of HABs
It is unclear what causes HABs; their occurrence in some locations appears to be entirely natural, while in others they appear to be a result of human activities Furthermore, there are many different species of algae that can form HABs, each with different environmental requirements for optimal growth. The frequency and severity of HABs in some parts of the world have been linked to increased nutrient loading from human activities. In other areas, HABs are a predictable seasonal occurrence resulting from coastal upwelling, a natural result of the movement of certain ocean currents. The growth of marine phytoplankton (both non-toxic and toxic) is generally limited by the availability of nitrates and phosphates, which can be abundant in coastal upwelling zones as well as in agricultural run-off. Coastal
water pollutionWater pollution is the contamination of water bodies such as lakes, rivers, oceans, and groundwater. All water pollution affects organisms and plants that live in these water bodies and in almost all cases the effect is damaging either to individual species and populations but also to the natural...
produced by humans and systematic increase in
sea water temperatureGlobal warming is the increase in the average temperature of the Earth's near-surface air and oceans since the mid-20th century and its projected continuation. Global surface temperature increased 0.74 ± 0.18 °C during the last century...
have also been suggested as possible contributing factors in HABs. Other factors such as iron-rich dust influx from large desert areas such as the Saharan desert are thought to play a major role in causing HABs. Some algal blooms on the Pacific coast have also been linked to natural occurrences of large-scale climatic oscillations such as El Niño events. While HABs in the Gulf of Mexico have been occurring since the time of early explorers such as Cabeza de Vaca, it is unclear what initiates these blooms and how large a role
anthropogenicAnthropogenic effects, processes or materials are those that are derived from human activities, as opposed to those occurring in biophysical environments without human influence....
and natural factors play in their development. It is also unclear whether the "apparent" increase in frequency and severity of HABs in various parts of the world is in fact a real increase or is due to increased observation effort and advances in species identification methods.
See also
- Algal bloom
An algal bloom is a rapid increase in the population of algae in an aquatic system. Algal blooms may occur in freshwater as well as marine environments. Typically, only one or a small number of phytoplankton species are involved, and some blooms may be recognized by discoloration of the water...
- Eutrophication
Eutrophication is an increase in the concentration of chemical nutrients in an ecosystem to an extent that increases in the primary productivity of the ecosystem...
- Red tide
Red tide is a common name for a phenomenon more correctly known as an algal bloom , an event in which estuarine, marine, or fresh water algae accumulate rapidly in the water column and results in discoloration of the surface water...
- Paralytic shellfish poisoning
Paralytic shellfish poisoning is one of the four recognized syndromes of shellfish poisoning . All four syndromes share some common features and are primarily associated with bivalve molluscs...
- Amnesic shellfish poisoning
Amnesic shellfish poisoning is a human illness caused by consumption of the marine biotoxin called domoic acid. This toxin is produced naturally by marine diatoms belonging to the genus Pseudo-nitzschia and, when accumulated in high concentrations by shellfish, can then be passed on to humans via...
- Neurotoxic shellfish poisoning
Neurotoxic Shellfish Poisoning is caused by the consumption of shellfish contaminated by brevetoxins or brevetoxin analogs.Symptoms in humans include vomitting and nausea and a variety of neurologic symptoms such as slurred speech. No fatalities have been reported but there are a number of cases...
- Ciguatera fish poisoning
- Diarrheal shellfish poisoning
Diarrhetic shellfish poisoning is one of the four recognised symptom types of shellfish poisoning, the others being paralytic shellfish poisoning, neurotoxic shellfish poisoning and amnesic shellfish poisoning....
External links
- Harmful Algae and Red Tide Information from the Coastal Ocean Institute, Woods Hole Oceanographic Institution
The Woods Hole Oceanographic Institution is a private, nonprofit research and higher education facility dedicated to the study of all aspects of marine science and engineering and to the education of marine researchers. Established in 1930, it is the largest independent oceanographic research...
- GEOHAB: The IOC-SCOR International Research Programme on the Global Ecology and Oceanography of Harmful Algal Blooms [SCOR and IOC of UNESCO
- Harmful Algal Bloom Programme of the Intergovernmental Oceanographic Commission of UNESCO [IOC of UNESCO
- International Society for the Study of Harmful Algae [ISSHA
- Toxic Blooms: Understanding Red Tides, a seminar by the Woods Hole Oceanographic Institution
The Woods Hole Oceanographic Institution is a private, nonprofit research and higher education facility dedicated to the study of all aspects of marine science and engineering and to the education of marine researchers. Established in 1930, it is the largest independent oceanographic research...
- NOAA Marine Biotoxins Program, National Oceanic and Atmospheric Administration
The National Oceanic and Atmospheric Administration is a scientific agency within the United States Department of Commerce focused on the conditions of the oceans and the atmosphere...
- Gulf of Mexico Dead Zone and Red Tides
- Red Tide updates for the Gulf Coast of Florida provided by Mote Marine Laboratory
Mote Marine Laboratory is a not-for-profit research and educational institution with an aquarium open to the public 365 days a year....
in Sarasota, FL
- California Program for Regional Enhanced Monitoring for PhycoToxins, California Department of Health Services and the University of California, Santa Cruz
The University of California, Santa Cruz, also known as UC Santa Cruz or UCSC, is a public, collegiate university; one of ten campuses in the University of California...
- Red Tide FAQ, Florida's Fish and Wildlife Research Institute
- Red Tide Report A Compilation of citizen based, media and official reports of the locations and severity of current Red Tide Blooms.
- Florida Red Tide Coalition A citizen based group dedicated to raising awareness of Red Tide, debunking myths, educating the public and taking action to promote or oceans health and help stop red tide.
- NIEHS study of airborne impacts of Florida red tide
- Washington State Shellfish Biotoxin Program