By Colleen Henn
- Causes of Bloom Formation
- Health Effects
- Health Guidelines and Policies
- Resources : Fact Sheets & Case Studies
- Learn about Cyanobacteria and Cyanotoxins
- Overview of Cyanobacteria
- Overview of Cyanotoxins
- Species of Cyanobacteria that Produces Toxins
- The Most Commonly Found Cyanotoxins in the U.S.
- Blue-green algae and harmful algal blooms
- Summertime in Minnesota: When in doubt, best keep out!
- What are blue-green algae?
- What are harmful algal blooms?
- What are the possible health effects?
- Can animals be affected?
- What should I do if I see a bloom?
- How can we get rid of harmful algae blooms?
- What Is Cyanobacteria?
- Cyanobacteria Blooms
- Harmful Algal Blooms (HABs)
- Health Effects of Cyanotoxins
- Cyanobacteria in Coral Reef Ecosystems: A Review
- Frequently Asked Questions: Cyanobacteria/Blue-Green Algae
- Tracking the Path of Green Slime
- What’s Next
- Related Web Pages
- Evolutionary History of Photosynthetic Cyanobacteria
Blooms of Cyanobacteria, also known as blue-green algae, are affecting inland and coastal communities around the world. According to NOAA, harmful algal blooms have been reported in every U.S. coastal state.
Cyanobacteria are aquatic bacteria, and are some of the oldest living organelles on Earth. Because these water-dwelling bacteria photosynthesize, they are also referred to as “blue-green algae.” Cyanobacteria can be found in many different environments, including freshwater and marine ecosystems. Despite being named “blue-green algae,” blooms may appear in many different colors including red, yellow, brown, blue, and green, and often form a scum on the water’s surface.
There are many different types of Cyanobacteria, but not all produce toxins. Microcystin and Anatoxin are two of the more common toxins that are produced by Cyanobacteria, and in high concentrations can be very harmful to other organisms living in the same aquatic environment. Under optimal conditions such as warm temperatures, sunlight and plentiful nutrients such as nitrogen and phosphorous, cyanobacteria can grow in localized blooms. When these blooms form toxins, which is increasingly becoming problematic in areas of high nitrogen concentrations, there are a whole host of public health concerns as drinking contaminated water (see the Drinking Water Guide for more information), eating shellfish and or even swimming in affected waterways can cause serious health effects. For this reason, harmful algal blooms are monitored to protect drinking water and prevent recreational exposure.
Causes of Bloom Formation
To understand how and why harmful algal blooms form, it’s important to note that cyanobacteria tend to reproduce rapidly in water with the following conditions: elevated nutrient levels, high temperatures and still water.
Numerous human activities increase the levels of nutrients present in bodies of water, especially nitrogen which is a source of energy for bacterial growth. Sources of nitrogen that affect waterways include agricultural, urban and residential runoff, and especially inadequately managed wastewater from either sewage or septic systems. Nitrogen pollution threatens the health of water all over the world. For a detailed example of how nitrogen affects waterways and surrounding communities, view this video about nitrogen pollution in Long Island, New York.
Scientists are also beginning to link the increased frequency of harmful algal blooms to climate change and human activity. Worldwide, these blooms are increasing in magnitude, frequency, and in geographical spread. With warmer temperatures associated with climate change, cyanobacteria are blooming in more northern latitudes. Stormwater associated with climate change induced high intensity rainfall, carries nitrogen and phosphorus into surface waterways. Because cyanobacteria also grow well in still water, blooms are becoming more frequent in rivers that have been dammed to create reservoirs.
With a rapidly changing climate, warmer weather, more intense rainfall, and pollution caused by human activity, we are perpetuating optimal conditions for harmful algal blooms. In high densities, these algae may discolor the water and outcompete other life forms.
There are numerous health and ecological effects associated with toxic cyanobacteria blooms. Humans are at risk to exposure while recreating in affected waters through ingestion, skin contact, and when airborne droplets containing the toxins are inhaled while swimming. Humans are also exposed to cyanobacteria when consuming shellfish from water bodies containing a high concentration of cyanotoxins. As stated by Markain Hawryluk with the Bend Bulletin, “microgram for microgram, the toxin is more deadly than cobra venom.”
Although humans are at risk of exposure, it is very hard for officials to track cases of human illness caused by harmful algal blooms because minor symptoms are overlooked. The effect of cyanobacteria on human health varies with the type of toxin present, its concentration, and the duration of exposure. The higher the concentration of cyanotoxin and the longer the exposure, the more severe the symptoms may be. Health effects usually occur when exposed to a high concentration, but some people may be more susceptible to developing symptoms.
Skin contact with cyanotoxins can cause irritation of the skin (rash or skin blisters), eyes, nose and throat, and inflammation of the respiratory tract. Swallowing water containing high concentrations can lead to nausea, vomiting, abdominal pain and diarrhea. Effects on the liver and nervous system of animals and people have also been documented in severe cases.
Dogs, livestock and other animals that drink water from affected areas or lick their fur to clean it are at a much higher risk of toxins than humans. Animals usually drink from areas on the edges of affected water, where algae tend to accumulate. Livestock and pet deaths have occurred after these animals have consumed large amounts of toxic algal scum accumulated along shorelines.
Health Guidelines and Policies
The Environmental Protection Agency (EPA) issued an advisory for the amount of cyanobacteria in drinking water, and after several years in development, the EPA released Recreational Water Quality Criteria or Swimming Advisories for Cyanotoxins in May 2019.
The EPA’s recommended identify the following concentrations of microcystins and cylindrospermopsin that would be protective of human health given a primary contact recreational exposure scenario: 8 µg/L for microcystins and 15 µg/L for cylindrospermopsin… Given that cyanobacterial blooms typically are seasonal events, recreational exposures are likely to be episodic, and may be short-term in nature. If adopted as a , for impairment assessment and listing purposes, the EPA recommends states and authorized tribes use 10-day assessment periods, not a rolling 10-day period, over the course of a recreation season to evaluate ambient water body condition and recreational use attainment.
Due to the risk associated with recreational exposure to cyanotoxins, the EPA developed these criteria recommendations under the Clean Water Act (Ambient Water Quality Criteria) to protect human health while swimming or participating in other recreational activities in and on the water. The EPA has also provided additional resources to help people stay safe and informed.
While EPA was in the process of developing their cyanotoxin guidelines, some states developed their own criteria for recreational exposure to cyanotoxins. Twenty-one states have implemented harmful algal bloom response guidelines when there is a bloom present. These guidelines are usually based on the visible presence of scum on the surface, cell count, and toxin (microcystin and anatoxin) levels. For example, the state of Massachusetts suggests avoiding contact with water when there are 14 micrograms of Microcystin per liter of water and anything greater than or equal to 70,000 cell count of cyanobacteria per milliliter of water. In addition to Microcystin, the state of Oregon releases a Public Health Advisory when four other cyanotoxins are above state-recommended limits.
Currently, toxin measurements require that samples be collected and analyzed in a laboratory, but one study shows that could be developed to estimate and predict cyanobacterial blooms at freshwater sites given several predictor variables. “Models provide the opportunity for public health protection prior to exposure and allow users to be proactive rather than reactive.” These models provide an opportunity to predict where blooms may occur and therefore target priority areas to propose solutions.
Map of freshwater algae bloom reports (including toxic and non-toxic blooms) from 2010 to 2019. For an interactive version .
The increased local and national coverage of the growing threat that cyanobacteria blooms and their toxins pose to recreation, public health, and local economies, has created in many locations the public awareness and political will to start solving water pollution problems. There are also ways all of us can take action at home to support clean water and prevent nutrient pollution from getting into local waterways and causing cyanobacteria to bloom.
Our elected officials need to pay attention to this public health and economic crisis and take action to control the flow of pollution into the waterways and beaches that drive our coastal tourism economy. See below for actions local community members, cities, and states can do to stop future severe algae blooms:
Actions we can all take:
- Scoop the Poop. Pick up your pet’s waste.
- Wash your car over grass or gravel, not on the street. Better yet take it to a commercial car wash.
- Maintain your cesspool or septic system through proper inspection practices and not pouring harsh chemicals down the drain.
- Make your yard more Ocean Friendly:
- Go organic. Stop using chemical fertilizers and pesticides.
- Apply mulch and compost to build healthy living soil instead.
- Plant native and climate-appropriate plants.
- Direct rain gutters and downspouts into your landscaping to slow down and sponge up rain. Learn more here.
- Show up at City Council and demand the actions below.
Local jurisdictional actions could include:
- Conduct mandatory septic tank inspections.
- Post beach closures and health advisories quickly and publicly.
- Pass strong local fertilizer restrictions (see Manatee County for a good example).
- Implement proactive programs to control stormwater pollution, such as Ocean Friendly Gardens.
- Inspect and maintain sewage infrastructure.
Statewide actions could include:
- Set and enforce stronger water quality standards and regulations.
- Help local communities transition away from septic systems to sewers (even when septics are functioning properly, they do not remove nitrogen from waste flow so it eventually seeps into ground and surface waters).
- Provide funding to local municipalities to inspect and maintain their sewage infrastructure.
- Regulate and restrict fertilizer inputs from agriculture into freshwater areas.
- Restore natural flow of water to the coast.
Efforts are even being made to take nuisance and harmful algae and make it into a useful product. For example, Bloomfoam is hoping to harvest freshwater algae from US waterways to make yoga mats and surf deck traction pads out of the final product. This effort could cut down on the need for new petroleum-base products and help to clean the water in affected areas. There are also efforts to convert algae into biofuel.
Resources : Fact Sheets & Case Studies
Understanding Algae Blooms
What are Algae Blooms and Why Are they Bad?
World Health Organization Guidelines for Safe Recreational Water Environments
Environmental Protection Agency Health and Ecological Effects
Environmental Protection Agency Cyanobacteria Fact Sheet
Environmental Protection Agency Guidelines and Recommendations
EPA – Partnering with States to Cut Nutrient Pollution
Center for Disease Control and Prevention Cyanobacteria
SeaGrant- Harmful Algal Blooms Facts
California Cyanobacterial and Harmful Algal Bloom Network (CCHAB)
Sacramento-San Joaquin Delta
San Bernardino County
Connecticut Department of Health- Blue–Green Algae Blooms in Connecticut Lakes and Ponds Fact Sheet
Statewide Department of Energy and Environmental Protection
Department of Natural Resources- Blue-Green Algae in Delaware
Florida Health- Harmful Algae Blooms
NOAA – Red Tide Forecast
Surfrider Coastal Blog – A Brief History of Florida’s Green Slime
Palm Beach County Chapter Algae Fact Sheet
Great Lakes Environmental Research Laboratory
Indiana Department of Natural Resources- Swimming, Boating and Harmful Algal Blooms
Illinois Department of Public Health- Harmful Algal Blooms
Maine Department of Environmental Protection- Cyanobacteria
Department of Public Health- Harmful Algae Blooms
Statewide Executive Office of Health and Human Services
Microcystis and Anabaena Fact Sheet
Department of Health- HAB Fact Sheet
Statewide Department of Environmental Services
Department of Environmental Services Fact Sheet
Department of Environmental Protection- Cyanobacterial HABs
Statewide Ecological Impacts
Northern New Jersey
Statewide Department of Environmental Conservation- Harmful Algal Bloom Notification Page
Department of Environmental Conservation- Harmful Algal Blooms and Marine Biotoxins
Eastern Long Island Chapter Algae Fact Sheet
SeaGrant- Harmful Algal Bloom FAQ
Department of Environmental Management- Harmful Algal Blooms
Statewide Department of Health
Statewide Department of Health
Statewide Current Lake Conditions
Statewide Department of Health
Department of Health Services- Understanding Algae
Learn about Cyanobacteria and Cyanotoxins
On this page:
Overview of Cyanobacteria
Blue-green algae, more correctly known as cyanobacteria, are frequently found in freshwater systems. They can also be found in estuarine and marine waters in the U.S. Cyanobacteria are often confused with green algae, because both can produce dense mats that can impede activities like swimming and fishing, and may cause odor problems and oxygen depletion; however, unlike cyanobacteria, green algae are not generally thought to produce toxins. Some freshwater cyanobacterial blooms or cyanoHABs are able to produce highly potent toxins, known as cyanotoxins.
Overview of Cyanotoxins
Cyanotoxins are produced and contained within the cyanobacterial cells (intracellular). The release of these toxins in an algal bloom into the surrounding water occurs mostly during cell death and lysis (i.e., cell rupture) as opposed to continuous excretion from the cyanobacterial cells. However, some cyanobacteria species are capable of releasing toxins (extracellular) into the water without cell rupture or death.
Species of Cyanobacteria that Produces Toxins
Cyanotoxins can be produced by a wide variety of planktonic cyanobacteria. Some of the most commonly occurring genera are Microcystis, Dolichospermum (previously Anabaena), and Planktothrix.
Microcystis is the most common bloom-forming genus, and is almost always toxic. Microcystis blooms resemble a greenish, thick, paint-like (sometimes granular) material that accumulates along shores. Scums that dry on the shores of lakes may contain high concentrations of microcystin for several months, allowing toxins to dissolve in the water even when the cells are no longer alive or after a recently collapsed bloom.
Species of the filamentous genus Dolichospermum form slimy summer blooms on the surface of eutrophic lakes and reservoirs. Dolichospermum blooms may develop quickly and resemble green paint. In less eutrophic waters, some species also form colonies, which are large dark dots in water samples and on filters after filtration.
Planktothrix agardhii forms long, slender, straight filaments that usually remain separate but form dense surface scums. Its presence may be revealed by a strong earthy odor and the filaments are easily detected visually in a water sample.
The Most Commonly Found Cyanotoxins in the U.S.
The most commonly found cyanotoxins in the U.S. are microcystins, cylindrospermopsin, anatoxins and saxitoxins.
Microcystins are produced by Dolichospermum (previously Anabaena), Fischerella, Gloeotrichia, Nodularia, Nostoc, Oscillatoria, members of Microcystis, and Planktothrix. Microcystins are the most widespread cyanobacterial toxins and can bioaccumulate in common aquatic vertebrates and invertebrates such as fish, mussels, and zooplankton. Microcystins primarily affect the liver (hepatotoxin), but can also affect the kidney and reproductive system. While there is evidence of an association between liver and colorectal cancers in humans and microcystins exposure and some evidence that microcystin-LR is a tumor promoter in mechanistic studies, EPA determined that there is inadequate information to assess carcinogenic potential of microcystins in humans due to the limitations in the few available human studies (i.e., potential co-exposure to other contaminants) and lack of long-term animal studies evaluating cancer following oral exposure.
Cylindrospermopsin is usually produced by Raphisiopsis (previously Cylindrospermopsis), raciborskii (C. raciborskii), Aphanizomenon flos-aquae, Aphanizomenon gracile, Aphanizomenon ovalisporum, Umezakia natans, Dolichospermum (previously Anabaena) bergii, Dolichospermum lapponica, Dolichospermum planctonica, Lyngbya wollei, Rhaphidiopsis curvata, and Rhaphidiopsis mediterranea. The primary toxic effects of this toxin are damage to the liver and kidney. Following the EPA Guidelines for Carcinogen Risk Assessment, there is inadequate information to assess carcinogenic potential of cylindrospermopsin.
Anatoxins bind to neuronal nicotinic acetylcholine receptors affecting the central nervous system (neurotoxins). There are multiple variants, including anatoxin-a, homoanatoxin-a, and anatoxin-a(s). These toxins are mainly associated with the cyanobacterial genera Chrysosporum (Aphanizomenon) ovalisporum, Cuspidothrix, Raphisiopsis (previously Cylindrospermopsis), Cylindrospermum, Dolichospermum, Microcystis, Oscillatoria, Planktothrix, Phormidium, Dolichospermum (previously Anabaena) flos-aquae, A. lemmermannii Raphidiopsis mediterranea (strain of Raphisiopsis raciborskii), Tychonema and Woronichinia. There is no information available on the carcinogenicity of anatoxin-a in humans or animals or on potential carcinogenic precursor effects.
Saxitoxins are representative of a large toxin family referred to as the Paralytic Shellfish Poisoning (PSP) toxins. When toxigenic marine dinoflagellates are consumed by shellfish, toxins concentrate and are delivered to consumers of the shellfish. These toxins have been reported also in freshwater cyanobacteria including Aphanizomenon flos–aquae, Dolichospermum (previously Anabaena) circinalis, Lyngbya wollei, Planktothrix spp. and a Brazilian isolate of Raphisiopsis raciborskii.
More information on on cyanobacteria and cyanotoxins:
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Blue-green algae and harmful algal blooms
Summertime in Minnesota: When in doubt, best keep out!
When temperatures climb and the summer sun beats down, conditions are ripe for Minnesota lakes to produce harmful algae blooms, some of which can be harmful to pets and humans.
What are blue-green algae?
Blue-green algae are not algae at all, but types of bacteria called cyanobacteria that are normally present in many lakes. This type of bacteria thrives in warm, nutrient-rich water. When conditions are right, the bacteria can grow quickly forming “blooms.”
What do blue-green algal blooms look like?
Blue-green algal blooms are often described as looking like pea soup or spilled green paint. However, blooms aren’t always large and dense and can sometimes cover small portions of the lake with little visible algae present. Blooms can also produce a swampy odor when the cells break down. Here are some examples of algae blooms.
A couple of easy tests can tell you if the green stuff you’re seeing in your body of water is likely to be blue-green algae:
What are harmful algal blooms?
When blue-green algal blooms produce cyanotoxins (toxins produced by cyanobacteria) that can make humans and animals sick, they are considered harmful. In general, algae are not harmful.
When do harmful algal blooms occur?
Blue-green algae prefer warm, calm, sunny weather and water temperatures higher than 75 °F. Blooms usually occur during summer and early fall, but can occur other times of the year, if conditions are right.
Where are harmful algal blooms found?
Harmful algae can be found everywhere in Minnesota, but thrive in warm, shallow, nutrient-rich lakes. They will often be found on the downwind side of a lake or in a secluded bay or shoreline.
What are the possible health effects?
You can become sick if you swallow, have skin contact with, or breathe in airborne water droplets while swimming, boating, waterskiing, tubing, bathing, or showering in water that has harmful algae or if you drink water that contains algal toxins. If you become sick, you might experience vomiting, diarrhea, rash, eye irritation, cough, sore throat, and headache. Symptoms generally begin hours to two days after exposure.
What should I do if I see blue-green algae in my drinking water source?
Avoid using untreated lake or river water for drinking, cooking, and brushing teeth, particularly for infants and small children. Boiling water will not destroy toxins and could actually increase toxin levels. Simple treatment options are also not effective, because multiple treatment steps are typically required to remove algal toxins.
Water that may be contaminated can be used for handwashing, bathing, washing dishes, or laundry, though it may irritate skin. Young children should be supervised when bathing to prevent them from swallowing water. After washing, skin and items that go into the mouths of infants and young children (i.e., teething rings, nipples, bottles, toys, and silverware) should be rinsed with uncontaminated water.
Can animals be affected?
Pets, especially dogs, are susceptible to harmful algae because they swallow more water while swimming and doing activities like retrieving a ball from the water. They are also less deterred by green, smelly water that may contain harmful algae. Animals can experience symptoms within minutes of exposure to the toxins. Symptoms they might experience include vomiting, diarrhea, weakness, difficulty breathing, and seizures. In the worst cases, animals have died. If your pet experiences these symptoms after exposure to algae, contact your veterinarian.
What should I do if I see a bloom?
There is no way to tell if a blue-green algal bloom is toxic just by looking at it. Adults, children, and animals should avoid contact with water with blue-green algae. Toxins can persist in the water after a bloom; watch for signs of recent blooms, such as green scum on the shoreline. When in doubt, stay out! If you or your pet go into water where there may be a bloom, wash off with fresh water immediately afterwards.
How can we get rid of harmful algae blooms?
We can’t eliminate blue-green algae from a lake — they are an inherent part of the overall algal community. What we really want to do is control their overall intensity and the frequency of the blooms. Since we can’t control the water temperature, the best thing we can do is to reduce the amount of nutrients getting into the lake. This can best be accomplished by reducing the amount of phosphorus and nitrogen from man-made sources such as lawn fertilizer, and runoff from cities, cultivated fields, feedlots, and a myriad of other sources. Though a reduction of nuisance algal blooms will not be immediate, it is the best long-term solution to minimizing the frequency and intensity of algal blooms.
Photos of non-toxic plants and algae
Chara, a form of filamentous algae often found in lakes with good water clarity
Duckweed, a non-toxic aquatic plant often mistaken for algae
Filamentous green algae, a non-toxic form of algae that can create recreational nuisances
What Is Cyanobacteria?
Cyanobacteria, or “blue-green algae,” form mats on the surface of water and can produce toxins that are harmful to humans and dogs.
Cyanobacteria are a group of bacteria found throughout the world.
They grow in any type of water (fresh, brackish, or marine) and are photosynthetic: They use sunlight to create food and survive.
Normally microscopic, cyanobacteria can become clearly visible in warm, nutrient-rich environments, which allow them to grow quickly and “bloom” in lakes and other bodies of water.
These bacteria are commonly known as “blue-green algae” because of their color, texture, and aquatic location, but they’re not plants like true algae.
Blooms of cyanobacteria — when the population of cyanobacteria explodes — typically occur in still or slow-moving water, such as lakes, ponds, and weak streams, when the water is warm, gets plenty of sunlight, and is rich in nutrients like phosphorous and nitrogen.
In the United States, these blooms occur most often in summer and early fall, although they can occur any time of year, according to the Centers for Disease Control and Prevention (CDC).
Because most cyanobacteria species float in water, blooms often appear as foam, scum, or mats on the water’s surface, and can cause clear water to become cloudy.
Though typically blue-green in color, cyanobacteria blooms can also be blue, bright green, brown, or red, resembling paint floating on the water.
In some cases, cyanobacteria blooms don’t affect the water’s appearance, making it difficult to know if a bloom is occurring.
At the end of a bloom, when the cyanobacteria are dying off, the water may smell bad.
Harmful Algal Blooms (HABs)
Cyanobacteria can be helpful by providing nutrients to plants such as rice and beans.
However, cyanobacteria blooms can also be dangerous. Cyanobacterial harmful algal blooms — known as HABs or CyanoHABs — can use up the oxygen in water and block sunlight that freshwater plants and animals need to survive.
Some cyanobacteria also produce potent toxins, called cyanotoxins, during CyanoHABs.
In the United States, the most common cyanotoxin-producing varieties are Microcystis, Anabaena, and Oscillatoria, which produce toxins in the microcystin, cylindrospermopsin, anatoxin, and saxitoxin classes, according to the Environmental Protection Agency (EPA).
Health Effects of Cyanotoxins
Exposure to cyanotoxins, caused by drinking or swimming in contaminated water, or breathing air containing cyanobacteria or their toxins, can affect the skin, nervous system, and liver.
A wide range of symptoms can develop from cyanotoxin exposure, including:
- Skin irritation and rashes
- Stomach cramps
- Nausea and vomiting
- Sore throat
- Muscle and joint pain
- Mouth blisters and ulcers
- Allergic responses
- Trouble breathing
- Burning or tingling in fingers and toes
- Slurred speech
- Increased salivation
Life-threatening liver damage may also develop in people exposed to cyanobacteria through contaminated dialysis water.
Dogs often become victims of cyanobacteria blooms when they swim in or drink contaminated water.
Cyanobacteria blooms killed approximately 100 dogs between 2002 and 2012, according to a 2013 CDC-led study in the journal Toxins.
However, this figure most likely underestimates the true number of deaths, because the CDC only surveyed 13 states.
Cyanobacteria in Coral Reef Ecosystems: A Review
Opisthobranchs may also play a role in top-down control of toxic cyanobacterial blooms, as was demonstrated for toxic Lyngbya by Capper and Paul .
Microbial mats can also be ingested by filter feeders. Identification of homoanatoxin-a from benthic marine cyanobacteria (Hydrocoleum lyngbyaceum) samples collected in Lifou (Loyalty Islands, New Caledonia) was recently reported . This cyanobacterium was suspected to cause giant clam (Tridacna maxima) intoxications.
3. Planktonic Cyanobacteria
Planktonic cyanobacteria found in coral reef plankton are mainly filamentous and unicellular.
3.1. Planktonic Filamentous Cyanobacteria
Large blooms of Trichodesmium, a filamentous nitrogen-fixing cyanobacterium, are observed frequently in coral reef ecosystems . They have been documented in the eastern Indian Ocean and western Pacific , in the central region of the Great Barrier Reef , in the Gulf of Thailand , and in the south-western Tropical Pacific . Trichodesmium spp. have been described to be nontoxic, sometimes toxic, or always toxic to a range of organisms . Recent studies have provided unprecedented evidence of the toxicity of Trichodesmium spp. from the New Caledonia lagoon , demonstrating the possible role of these cyanobacteria in ciguatera fish poisoning.
Trichodesmium is the most well-studied marine N2-fixing organism and perhaps one of the most important. The rate of nitrogen fixation by Trichodesmium species in surface waters is close to 2 pmol N trichome-1 h−1 . It is difficult to quantify the importance of Trichodesmium diazotrophy because of the stochastic nature of the blooms. However, it is estimated that Trichodesmium contributes about 0.03–20% of the total CO2 fixation in the coastal surface waters of Tanzania .
The pelagic harpacticoid copepod Macrosetella gracilis is usually found in association with blooms of Trichodesmium in tropical and subtropical waters. This copepod is one of the few direct grazers of these often toxic cyanobacteria .
The study of Villareal in the Belizean barrier reef showed significant grazing of Trichodesmium by the coral reef community.
3.2. Planktonic Unicellular Cyanobacteria
Oligotrophic waters surrounding coral reef ecosystems and lagoons are dominated by the small coccoid unicellular cyanobacteria Synechococcus and Prochlorococcus . In coral reef waters, Synechococcus has a size of 1 μm and an abundance ranging from 10 × 103 to 500 × 103 cells mL−1, while Prochlorococcus has a size of 0.6 μm and an abundance ranging from 10 × 103 to 400 × 103 cells mL−1.
The contribution of unicellular cyanobacteria to phytoplankton biomass and production varies according to the ecosystem. In Tuamotu lagoon (French Polynesia), Synechococcus is the predominant group in terms of abundance and carbon biomass and has the highest planktonic primary production among lagoons. As it is generally scarce in deep water with limited light availability, its biomass contribution is reduced in deep lagoons. In very shallow lagoons, no general trend has been observed, as the dominant group appears to depend on the water residence time within the lagoon . In Tuamotu lagoon and Miyako Island (Okinawa) picoplankton primary production represents 65–80% of total phytoplankton production .
Ayukai reported that on the Great Barrier Reef, the average abundance of cyanobacteria (Synechococcus) is 0.16–2.41 × 104 cells mL−1. Later, Crosbie and Furnas , using a flow cytometer, observed that Synechococcus was more abundant and had a greater biomass than Prochlorococcus at most inshore and mid-shelf sites in central regions (17°S) and at all shelf sites in southern areas (20°S) of Great Barrier Reef. Moreover, Synechococcus and Prochlorococcus abundance was better correlated with salinity, shelf depth, and chlorophyll a concentration than with nutrient concentrations.
At Sesoko Island (Okinawa), Tada et al. found that picoplankton dominated the phytoplankton community with an average contribution to the total chlorophyll-a biomass of 52%. At Miyako Island (Okinawa, Japan), the contribution of picophytoplankton to total phytoplankton biomass is 45–100% . In another study, Ferrier-Pagès and Furla found that the picophytoplankton contribution to total chlorophyll was 32–73%. Prochlorococcus, Synechococcus, and picoeukaryote abundance was on average 64 ± 11, 12 ± 2, and 4 ± 0.7 × 103 cells mL−1, respectively. Their contribution to picoplankton biomass was 10, 49, and 41%, respectively, and the contribution of picoplankton primary production to total phytoplankton production is 65%. On Miyako Island, Okinawa (Japan), Synechococcus spp. represented 65% of the chlorophyll (<3 μm), 53% of autotrophic carbon, and 67% of the nitrogen . In Mayotte (south-western Indian Ocean), particles <10 μm accounted for 74% of the chlorophyll-a concentration and for 47% of the total living carbon .
In one study in New Caledonia’s coral lagoon, unicellular diazotrophic cyanobacteria of 1–1.5 μm were found along a nutrient gradient using whole-cell hybridization with specific Nitro 821 probes . Their abundance ranged from 3 to 140 cells mL−1. These cells may contribute to N2 fixation (from the <10 μm size fraction) which was estimated to be 4.4–8 nmol N−1 d−1.
Very few studies have investigated grazing of unicellular cyanobacteria in coral reef waters . In Tikehau lagoon (Tuamotu),Gonzálezet al. showed that phagotrophic nanoflagellates were the major grazers of picocyanobacteria. Ciliates and heterotrophic dinoflagellates appeared to be grazing mostly on nanoplankton, both autotrophic and heterotrophic cells, showing the important contribution of coccoid cyanobacteria to the microbial food web.
In Takapoto (Tuamotu), the grazing rates of <200 μm protozoa on cyanobacteria represented 74% of their growth rates . In the lagoonal waters of the two largest atolls of French Polynesia (Rangiroa and Fakarava), 75% of the cyanobacteria production was consumed by <10 μm fractions, equal to 0.05–0.5 × 104 cyanobacteria mL-1 h−1 . In the water over a fringing coral reef at Miyako Island (Japan), 30–50% of picocyanobacteria production was grazed by heterotrophic flagellates and ciliates, which themselves were grazed (50–70% of the production) by higher trophic levels .
On Conch Reef, Florida Keys, sponges are a net sink for picocyanobacteria . In the Gulf of Aqaba, Red Sea, measurements of depletion of phytoplankton cells and pigments over coral reefs have revealed that Synechococcus contributes >70% of the total depleted carbon in summer. The grazing of cyanobacteria appears to be an important component of benthic-pelagic coupling in coral reefs . Another study by Yahel et al. demonstrated that sponges removed significant amounts of picocyanobacteria but suggested that DOC may play a major role in the trophic dynamics of coral reefs. In Caribbean coral reef communities, gorgonian corals do not appear to graze significantly on picocyanobacteria .
In addition, they have the following.(i)They help build and erode the reef.(ii)They are important primary producers.(iii)They represent an organic source for planktonic and benthic heterotrophic organisms.(iv)They enrich the ecosystem with nitrogen.
This work was supported by the Institute of Research for Development (IRD) and by grants from the Ocean Development Sub-Committee of France-Japan S&T Cooperation, Mitsubishi cooperation, the Ministry of Education, Science, Sport, and Culture of Japan.
Frequently Asked Questions: Cyanobacteria/Blue-Green Algae
What are cyanobacteria/blue-green algae? Blue-green algae are a group of organisms that can live in freshwater, salt-water or in mixed “brackish” water. Most of us know them as “pond scum.” They also have been found to share some characteristics with bacteria, which has led to them being referred to as “cyanobacteria.”
What is a cyanobacterial bloom and how do they form? Cyanobacterial blooms occur when the algae that are normally present grow in numbers more than normal. Within a few days, a bloom can cause clear water to become cloudy. Winds tend to push some floating blooms to the shore where they become more noticeable. Cyanobacterial blooms can form in warm, slow moving waters that are rich in nutrients. Blooms can occur at any time, but most often occur in late summer or early fall. They can occur in marine, estuarine and fresh waters, but cyanobacteria blooms that can cause concern are those that occur in fresh water, such as drinking water reservoirs or recreational waters.
What do cyanobacterial blooms look like? Some cyanobacterial blooms can look like foam, scum, or mats on the surface of fresh water lakes and ponds. The blooms can be blue, bright green, brown, or red and may look like paint floating on the water. Some blooms may not affect the appearance of the water. As algae in a cyanobacterial bloom die, the water may smell bad.
What are some tips for avoiding cyanobacteria/blue-green algae? It is important that adults, children and pets avoid swimming in or drinking water containing blue-green algae. It is best not to come in to contact with water in areas where you see foam, scum, or mats of algae on the water.
What should I do if I come in contact with cyanobacteria/blue-green algae? In high amounts, cyanobacteria toxins can affect the liver, nervous system and skin. Abdominal cramps, nausea, diarrhea, and vomiting may occur if untreated water is swallowed. Some people who are sensitive to the algae may develop a rash or respiratory irritation. If you come into contact with an algae bloom, wash with soap and water right away. If you experience an illness, please contact your healthcare provider.
What agency should I contact to report fish kills, algal blooms or illness associated with blue-green algae? Fish Kill Hotline (Florida Fish & Wildlife Conservation Commission) 1-800-636-0511 Bloom Reporting (Florida Department of Environmental Protection) 1-855-305-3903 Human Illness (Florida Poison Control Center) 1-800-222-1222
Can I eat fish harvested from areas near or in algae blooms? Fish tested from water with blue-green algae blooms show that the cyanotoxins from algae do not accumulate much in the edible portion of fish which is the muscle or fillet meat. Exposure to cyanotoxins from catching and eating the fish from areas with blue-green algae is minimal. Many lakes and rivers in Florida are large with blooms not covering the entire water body. Most of the fish are not in the area where blooms exist. Blooms also tend to be temporary, especially by place and time as they move around due to wind, waves and currents. We suggest that people do not harvest fish near or in the blooms.
Is it OK to use algae water for showering or irrigation? Untreated water from the bloom area should not be used for irrigation when people could come into contact with the spray. Do not use untreated water from an area with a bloom for showering or bathing.
Where is there more information on algal blooms and health? Additional information on health issues related to algal blooms is available on the DOH website http://www.floridahealth.gov/healthy-environments/aquatic-toxins/index.html, and the US Centers for Disease Control and Prevention webpage: https://www.cdc.gov/habs/index.html.
Tracking the Path of Green Slime
Andrew Knoll of Harvard University calls cyanobacteria the “microbial heroes of Earth’s history.”
Most life on Earth owes its existence to tiny organisms called cyanobacteria. These primitive bacteria gave us oxygen for the atmosphere and a protective ozone layer, and they led to the development of all the green plants in the world today.
“Cyanobacteria are the microbial heroes of Earth history,” says Andrew Knoll, a professor of evolutionary biology at Harvard University. “They are the inventors of ‘green plant’ photosynthesis and the ultimate source of breathable air.”
Of course, when cyanobacteria first appeared, the other life forms on Earth weren’t too happy about it. It was as though an ill-mannered cousin showed up with a big stinky cigar, blowing smoke right in their faces. Only in this case, the smoke was a poisonous gas known as oxygen. Untold numbers of organisms were wiped out as cyanobacteria released oxygen into the atmosphere. If they were lucky, the stressed organisms managed to hide away in places where oxygen couldn’t reach – deep down in anoxic mud or in the cracks and crevices of hydrothermal vents under the sea. The offspring of these survivors can still be found living in these places today.
Cyanobacteria, too, are still around today. They can be found everywhere from the surface of the oceans to underneath rocks in the desert. They can live in bright light or low light, in salt water and fresh, in extreme cold or heat, with oxygen or without it. In fact, cyanobacteria are so widespread that J. William Schopf, professor of paleobiology at UCLA, calls cyanobacteria, “evolution’s most successful ecologic generalists.”
Not only can cyanobacteria live just about anywhere, but they’ve also managed to survive throughout much of Earth’s biotic history. Whatever ecological catastrophes fate has thrown at the Earth – be it another Ice Age, a large asteroid impact, or changes in the atmosphere – through it all cyanobacteria have survived.
“Like fantastic aliens of a class B movie,” Schopf writes in his book, ‘Cradle of Life,’ “they’ve proven impossible to wipe out, surviving on and on as life around them has gone extinct.”
And, even more extraordinarily, cyanobacteria appear to have survived relatively unchanged. Schopf says that they do not look appreciably different from the cyanobacteria of two billion years ago. How could cyanobacteria be so untouched by the processes of evolution, when in the same amount of time the rest of life evolved from a single celled organism to the vast range of forms we see today, including our own human species?
As it turns out, different organisms experience different rates of evolution. Some organisms, like insects, evolve quickly. That’s why pesticides stop being effective after a certain period of time – those that can tolerate the pesticide survive to breed, and before you know it all the offspring are immune. Others, like cyanobacteria, evolve more slowly.
Pictured above are two kinds cyanobacteria from the Bitter Springs chert of central Australia, a site dating to the Late Proterozoic, about 850 million years old. On top is a colonial chroococcalean form, and on the bottom is the filamentous Palaeolyngbya.
Another reason cyanobacteria have been able to get away with so little evolutionary change is because of their ability to live almost anywhere. Evolution is often propelled by the need to adapt to environmental change. In addition, cyanobacteria reproduce non-sexually. The vast numbers of possible genetic combinations that we see in sexually reproducing organisms just don’t occur with cyanobacteria.
Evolution hasn’t completely by-passed cyanobacteria. There is evidence that some modern cyanobacteria are more sophisticated than their ancestors, forming communities with a range of adaptations to maximize their share of the available light and nutrients. But because cyanobacteria fossils look so similar to modern cyanobacteria, this suggests that some forms of cyanobacteria have changed very little over the years. This makes tracking their history in the fossil record difficult. Scientists would dearly like to know, for example, when cyanobacteria first came on the scene.
In 1993, Schopf made headlines when he claimed to find the earliest known fossilized life. These structures, which he described as “cyanobacterium-like,” were found in 3.5 billion-year-old chert (a type of silica rock) from Western Australia. Since his discovery, these ancient structures are often cited as the oldest fossilized life on Earth.
However, Schopf’s finding may not be as definite as the textbooks and news reports would have you believe. Some scientists contend that the shapes found by Schopf are not cyanobacteria, or even fossilized life forms at all. Martin Brasier of Oxford University leads the opposition against Schopf’s claims. Brasier says that rather than being biological fossils, these structures are chemical artifacts formed from hydrothermally-heated graphite. The debate rages on, and many scientists are conducting their own studies of the enigmatic structures in an effort to find the truth.
Another controversial topic in the debate over cyanobacteria is the existence of Archaean stromatolites. These layered rock formations are formed by cyanobacteria. The bacteria live in a colonial layer called a “microbial mat.” When too many minerals and sediments became trapped in the sticky mat, sunlight can no longer penetrate and photosynthesis becomes impossible. The cyanobacteria then migrate up, creating a new mat layer on top of the old. This process occurs again and again, creating multiple sediment layers over time.
The existence of stromatolites dating back to nearly 3.5 billion years ago suggests that cyanobacteria were hard at work during the Archaean era. But not all stromatolites are formed by cyanobacteria; natural geological processes can build similar structures. Some have argued, therefore, that the ancient rock structures were formed by chemical precipitation or by the deformation of soft sediments.
At the time of this writing, microfossils from the 2.2 billion-year-old Gunflint Chert – found in the Great Lakes region of the United States – are the earliest uncontested evidence for cyanobacteria.
“The origins of cyanobacteria are still mysterious,” says Roger Summons, a professor of biogeochemistry and geobiology at MIT. “However, because the genomes and the biochemistry of today’s cyanobacteria preserve some kind of evolutionary record, we can learn more about their earlier forms.”
Understanding when cyanobacteria first appeared would not only help answer many questions about early life, it also would help pin down when oxygen began to be an important part of the environment. But even if cyanobacteria did form the Archaean stromatolites, they might not have been producing oxygen. In order to develop oxygen-producing photosynthesis, cyanobacteria had to undergo a series of evolutionary steps.
A modern-day photosynthetic cell undergoes two simultaneous reactions, both of which rely on a separate kind of protein. Photosystem I protein molecules use the trapped energy in sunlight to convert carbon dioxide into carbon and oxygen. This provides food in the form of carbohydrates, lipids, proteins and nucleic acids – the building blocks of life. Photosystem II protein molecules use light energy to split water into hydrogen and oxygen for plant respiration.
But the first photosynthetic organisms didn’t produce oxygen. The most ancient photosynthetic bacterial species are purple and green bacteria. Purple bacteria and green, non-sulfur bacteria rely on Photosystem II for energy, while green sulfur bacteria use
Purple sulfur bacteria. The gold particles in the cells are globules of elemental sulfur.
Photosystem I. Cyanobacteria, algae and plants use both Photosystem I and II, and it is generally believed that the two Photosystems arose from a single evolutionary ancestor. However, another possibility is that there may have been some gene swapping between the two photosynthetic groups. Called “lateral gene transfer,” this type of gene sharing may have been common in life’s early days. Many believe that this could have been the means by which cyanobacteria gained access to the genes necessary for both Photosystems.
Another technique of early evolution is that cells could absorb other cells in an act of symbiosis. Rather than digest the absorbed cell as food, it would become a part of the devouring cell’s inner machinery. Cyanobacteria, it is thought, was absorbed by an early eukaryotic cell (a cell with a nucleus). The absorbed cyanobacteria became a chloroplast, the structure that is responsible for photosynthesis in modern plants.
“Cyanobacteria evolved further to be the chloroplasts of other photosynthetic organisms, particularly algae and the green plants,” says Summons. “Thus, cyanobacteria may be just ‘green slime’ to some, but they are the foundations of the ecosystems of all complex life.”
Schopf and his colleagues are intensely studying the 3.5 billion-year-old structures from the Australia chert. They are currently doing laser-Raman spectroscopy, atomic force microscopy, and ion microprobe carbon isotopic analyses to try to find out whether the structures are cyanobacteria.
Summons, meanwhile, is conducting studies of the molecular biomarkers of modern cyanobacteria with his colleague Kai Hinrichs at the Woods Hole Oceanographic Institution (WHOI). By working with biologists who are experts on cyanobacterial occurrence, culturing, and genetics – such as John Waterbury (WHOI), Penny Chisholm (MIT), and Linda Jahnke (NASA) – they hope to develop molecular signatures for cyanobacterial productivity in the oceans. Summons believes these studies will lead to new methods for recognizing cyanobacteria in the sedimentary record, and perhaps trace them back to their earliest ancestors.
Related Web Pages
Cyanosite: A Webserver for Cyanobacterial Research
Life in an Anoxic World
Dust Up Over Oldest Fossils
The following points highlight the nine Importance of Cyanobacteria.
1. They are one of the early colonizers of bare and barren areas. They provide suitable conditions for the growth of other organisms even in the most hostile environment.
2. Blue green algae function as food to several aquatic animals. Spirulina is regularly collected for human consumption in parts of Africa. Nostoc is similarly used in China. In Rajasthan Anabaena and Spirulina are collected from Sambar Lake and used as fodder and manure. Spirulina is very easily cultivated in tanks and can be used as a palatable protein rich food supplement for humans and animals.
3. Several cyanobacteria have the ability of nitrogen fixation. The filamentous forms possess special large pale cells or heterocyst’s for this. Some of the fixed nitrogen comes out as excretion. After death of cyanobacteria the substratum becomes rich in nitrogen. Such nitrogen fixing cyanobacteria are now regularly inoculated in the rice fields. This saves consumption of nitrogen fertilizers.
4. Nitrogen fixing cyanobacteria are often used for reclaiming usar soils, e.g., Nostoc, Anabaena. These cyanobacteria produce acidic chemicals for counteracting alkalinity of the soil and nitrogenous compounds which are generally deficient in these soils.
5. Antibiotic can be manufactured from extract of Lyngbia.
6. Species of Anabaena and Aulosira do not allow mosquito larvae to grow nearby. Such cyanobacteria can be inoculated in village ponds and rice fields to prevent the growth of mosquitoes.
7. Cyanobacteria can grow on the walls and roofs of buildings during the rainy seasons causing discolouration, corrosion and leakage.
8. They produce water blooms, imparting bad odour and colour to water bodies.
9. Some cyanobacteria produce toxins harmful to most aquatic animals. They may prove equally toxic to human beings drinking or bathing in such water. The important toxins producing cyanobacteria are Microcytic aeruginosa (= Anacystis cyanea), Anabaena flosaquae, Aphanizomenon flos-aquae.
Evolutionary History of Photosynthetic Cyanobacteria
A study of 41 genomes from uncultured microorganisms provides new information about the evolution of aerobic respiration in Cyanobacteria. Photosynthetic Cyanobacteria are thought to have changed the course of life’s evolution on Earth by playing an important role in the oxygenation of Earth’s atmosphere roughly 2.3 billion years ago. By examining the genomes of multiple Cyanobacteria, as well as other related bacterial lineages, researchers found evidence that photosynthesis likely evolved in Cyanobacteria multiple times. In addition, modern photosynthesis could have arisen from the fusion of two different photosynthetic systems via lateral gene transfer. The work provides important details about how and when cyanobacteria evolved to release oxygen via photosynthesis.
The paper, “On the origins of oxygenic photosynthesis and aerobic respiration in Cyanobacteria,” was published in the journal Science. The work was supported in part by NASA Astrobiology through the Exobiology & Evolutionary Biology Program.