<p>Red tides, a type of harmful algal bloom, color the water rusty orange along the coast of British Columbia in Canada.</p>
Red tides, a type of harmful algal bloom, color the water rusty orange along the coast of British Columbia in Canada.
Photograph by Julian Nieman/ Alamy
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These toxic algal blooms, some deep red in color, trigger a tide of effects on animals and humans.
ByJenny Howard
Published July 5, 2019
• 8 min read
Often deep red or brown in color, a typical red tide can be observed along a marine coast. A type of harmful algal bloom, red tides refer to toxic blooms of microscopic algae that occur worldwide. Within the United States, these blooms appear in three main coastal areas. They are caused by several different microorganisms, all phytoplankton that use light energy to grow. But they aren’t always red.
What are red tides?
At least three species of dinoflagellates and one diatom species are responsible for the toxic mess of red tides in the United States. These microscopic forms of algae produce toxins that can sicken humans and be fatal for marine animals.
Within the United States, red tides occur most commonly in the Gulf of Mexico, off California, and in the Gulf of Maine. In each of these locales, a different microorganism—present at low levels normally—generates the algal bloom when conditions align. (Read more about red tides in Australia.)
Gulf of Mexico
A type of toxic algae, Karenia brevis, lives in the Gulf of Mexico throughout the year at low concentrations. When environmental conditions, like temperature, nutrient levels, and wind, are right, the algae population explodes and huge blooms form. These blooms release massive amounts of brevotoxin into the ocean. With their characteristic red color, these red tides affect Florida, Louisiana, Alabama, and Texas.
Richard Stumpf, an algal blooms expert at the National Oceanic and Atmospheric Administration (NOAA), says red tides tend to occur in Florida every year. In Texas, they used to bloom every ten years, but now appear every three years. Louisiana and Alabama cases tend to appear more rarely, often only when hurricanes push blooms northwest from southwest Florida.
Even at relatively low levels, K. brevis can interact with other types of algae, worsening the overall red tide. In particular, a cyanobacterium, Trichodesmium, blooms in the Gulf of Mexico after iron-rich dust drifts over from Africa. The cyanobacteria consume nitrogen from the atmosphere and when they die, they provide K. brevis with a food source of crucial elements: phosphorous, nitrogen, and iron.
Gulf of Maine
In the Gulf of Maine, Alexandrium catanella and Alexandrium fundyense are the main culprits for red tides. The result tends to only turn the characteristic red color when it blooms and concentrates in a front, the boundary between two pooling water sources.
Alexandrium has a fascinating life strategy, feeding, aggregating to reproduce, and then resting on the ocean floor as a dormant hard cyst over the winter. When the water temperature exceeds 50°F, generally in late spring, the cysts “perk up,” says Stumpf, and swim up to the surface to start growing. Alexandrium produces the toxin saxitoxin, which remains in the gulf in low concentrations during the year and explodes during blooms.
During a bloom, filter-feeders like clams inadvertently consume the toxin as they filter the water for food (algae), and the toxin accumulates inside their tissues. At these much higher concentrations, the toxin poisons shellfish and if consumed, can lead to paralytic shellfish poisoning in people.
California
The Pseudonitzchia species of algae, forms of diatoms, more commonly create red tides off the coast of California. Some of these blooms can be harmless, because not all produce the toxin domoic acid. In contrast to dinoflagellates, which swim to access nutrients and light, diatoms float in the ocean and if nutrients abound, the algae bloom. If not enough nutrients are in the water, they die. Generally, these algae bloom in spring and summer, though the more toxic blooms often occur during the spring.
Alexandrium species are also found in California, first discovered there in 1927 after an outbreak of paralytic shellfish poisoning.
Red tide effects on animals
The neurotoxins produced by harmful algae blooms can cause massive fish kills, with dead fish washing up on shores by the thousands. The toxin works its way through the food web, with other species preying on the sick fish. Die-offs of many marine species, like whales and sea turtles, have been linked to red tides. The toxins can even produce a foam that causes seabirds to lose the waterproofing on their feathers, resulting in their death.
In Florida, manatees can be affected by brevotoxin, so much so that it can lead to respiratory problems or even death.
Red tide effects on humans
The effects of red tides don’t stop at animals. People can be sickened from the toxins in the water or in tainted shellfish. K. brevis, the dinoflagellate causing red tides in Florida, can cause respiratory problems, particularly for people with asthma or allergies.
Red tides cause an estimated $82 million in economic losses each year due to beach and fishing closures, including associated drops in tourism and seafood revenues.
Human Influences on red tides
Climate change complicates the frequency and occurrence of red tides. Wind and temperature are expected to increase with a warming planet. With more wind stirring up nutrients, dinoflagellates can get food easier. But diatoms prefer calmer conditions.
Scientists predict that climate change will increase the frequency and intensity of hurricanes, potentially moving blooms to new locations. In Florida, a red tide lasted for 17 months after big hurricanes blew through in 2004 and 2005. And in 2017 after Hurricane Irma, another giant red-tide imperiled the state.
Additionally, more nutrients, running into the ocean from excess fertilizer on farms or lawns, can contribute to blooms. K. brevis is increasing in Florida’s waters, more abundant year-round now than in the 1950s, most likely because of higher nutrients. If the algae don’t have enough nitrogen, it dampens the bloom, says Stumpf.
Potential Solutions
Treatments of aluminum sulfate are sometimes used to fight algal blooms in small lakes or canals, but is not effective in the much larger ocean. In the 1950s, scientists tried using copper sulfate. That killed the algae, but also everything else in the water.
The best “fix,” says Stumpf, is mitigation through forecasting. “Right now, red tides in Florida are a crisis. We are trying to make it an inconvenience,” he says.
Stumpf and a team of scientists have created red tide forecasts that are released biweekly to let people know how safe an area in Florida (and elsewhere in the Gulf of Mexico) is for recreation. The forecasts take advantage of satellite images to estimate the size and impact of a bloom. The NOAA team has also introduced a new tool, called HABscope, for citizen scientists to help collect data on blooms. A miniature microscope, the HABscope, , attaches to a smartphone and allows a user to capture short videos of water samples collected from different locations in Florida. Counting the number of microalgae cells in the water sample lets scientists determine the risk or severity of a bloom.
In the Gulf of Maine, crews in the late fall collect sediment samples to count the number of Alexandrium cysts. They incorporate that level into biological models to predict the number that will survive until the next season. Then, scientists combine that predicted number with salinity and ocean current data in physical models to help forecast how bad a bloom will be in the next year. Usually if they find a lot of cysts, the Gulf of Maine will have a larger bloom. But that’s not always the case, and scientists are still trying to figure out why the forecasts were off this year.
FAQs
What are red tides answer? ›
This bloom, like many HABs, is caused by microscopic algae that produce toxins that kill fish and make shellfish dangerous to eat. The toxins may also make the surrounding air difficult to breathe. As the name suggests, the bloom of algae often turns the water red.
What causes red tide algal blooms? ›Chemicals from farming, factories, sewage treatment plants and other sources can become dissolved in water on the land. This water, called runoff, eventually flows into the ocean and can cause algae to grow faster, leading to red tides.
What kind of algae causes red tide? ›Some algae species, like the dinoflagellate Karenia brevis, color the ocean surface a deep red, inspiring the name “red tide.” But not all red tides are red and not all of them even become dense enough to color the water.
What happens in a red tide? ›Red tides, also called harmful algal blooms (HABs), occur when microscopic algae multiply to higher-than-normal concentrations, often discoloring the water. Although more than 50 HAB species occur in the Gulf of Mexico, one of the most well-known species is Karenia brevis, the red tide organism.
Who causes red tide? ›Red tide is caused by microscopic organisms in the plankton, the drifting or weakly swimming sea life, that are the foundation of the ocean food chain. Specifically, dinoflagellates, a microscopic marine life form with two long slender appendages, are the organisms responsible for red tide.
Is red tide harmful? ›Swimming is safe for most people. However, the red tide can cause some people to suffer skin irritation and burning eyes. People with respiratory illness may also experience respiratory irritation in the water. Use common sense.
How long does red tide last? ›How Long Does a Red Tide Last? Red tides can last from days to months. The length of time that a plankton bloom continues depends on many things, such as available nutrients and sunlight, water temperature, changes in wind or surf conditions, competition with other species, and grazing by zooplankton and small fish.
How can we stop red tide? ›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.
How is red tide treated? ›For most people, symptoms are temporary when red tide toxins are in the air. Wearing a particle filter mask may lessen the effects, and research shows that using over-the- counter antihistamines may decrease your symptoms. Check the marine forecast. Fewer toxins are in the air when the wind is blowing offshore.
Is red tide natural? ›But while red tide itself is natural, scientists say there's evidence that massive blooms may be partly caused by human activities, such as fertilizers washing off farms and the discharge of fertilizer-laden water from Lake Okeechobee into the Gulf of Mexico.
What color is red tide? ›
Red tides, explained. These toxic algal blooms, some deep red in color, trigger a tide of effects on animals and humans. Often deep red or brown in color, a typical red tide can be observed along a marine coast. A type of harmful algal bloom, red tides refer to toxic blooms of microscopic algae that occur worldwide.
How long do algal blooms last? ›A bloom may be present in one cove of a lake and not visible the next day. If the whole lake or pond has a bloom, they typically last for several weeks until conditions in the lake change and the algae die and decompose.
When did red tide start? ›Red tides were documented in the southern Gulf of Mexico as far back as the 1700s and along Florida's Gulf coast in the 1840s. Fish kills near Tampa Bay were even mentioned in the records of Spanish explorers in the 1500s.
Does red tide affect eating fish? ›Whelks and moon snails can also accumulate dangerous levels of the toxin during red tide as they feed on contaminated shellfish. During red tide blooms, hard-shell clams, soft-shell clams, oysters, mussels, whelks, and moon snails harvested from areas affected by the blooms are not safe to eat.
Is red algae harmful to humans? ›Red tides, blue-green algae, and cyanobacteria are examples of harmful algal blooms that can have severe impacts on human health, aquatic ecosystems, and the economy. Algal blooms can be toxic. Keep people and pets away from water that is green, scummy or smells bad.
Why is algal bloom harmful? ›Under the right conditions, algae may grow out of control — and a few of these “blooms” produce toxins that can kill fish, mammals and birds, and may cause human illness or even death in extreme cases.
Can you swim in red tide? ›Most people can swim during red tide without serious risks, but it may cause symptoms such as skin irritation and a burning sensation in the eyes.
What is red tide in biology? ›red tide, discoloration of sea water usually caused by dinoflagellates, during periodic blooms (or population increases). Toxic substances released by these organisms into the water may be lethal to fish and other marine life. Red tides occur worldwide in warm seas.
How does red tide affect animals? ›Red tides can also lead to die-offs of invertebrates, including shrimp, sponges, sea urchins, crabs and certain shellfish. In most cases, it is unclear whether invertebrate die-offs occur because of exposure to toxins or the low-oxygen conditions resulting from blooms.
Where is red tide the worst? ›Beaches along Florida's central and southwest coast are most affected by red tide, including the beautiful beaches near Tampa Bay, Sarasota, Anna Maria Island, Sanibel and Captiva Island.
What does red tide smell like? ›
With every breeze of wind that comes inland, the red tide brings a strong and disgusting smell of rot. What is this? The red tide smells like gone off food that is a long way into the decaying process, and it is enough to turn the stomach of anyone who smells it. This is because it has a very sulfurous scent.
Are all algae blooms harmful? ›No, not all algal blooms are harmful.
These blooms occur when phytoplankton, which are tiny microscopic plants, grow quickly in large quantities while producing toxic or harmful effects on people, fish, shellfish, marine mammals, and birds.
Yes, red tide is dangerous to animals (including humans and dogs). “The K. brevis produces brevetoxins, which is a neurogenic toxin, affecting the central nervous systems of fish and other vertebrates, causing death,” Dr. Mears said.
Can red tide cause headaches? ›The algae produce a toxin that can not only choke animals but in humans cause headaches, sore throats, vomiting, diarrhea and pneumonia.
Is red tide natural or man made? ›But while red tide itself is natural, scientists say there's evidence that massive blooms may be partly caused by human activities, such as fertilizers washing off farms and the discharge of fertilizer-laden water from Lake Okeechobee into the Gulf of Mexico.
Can you swim in red tide? ›Most people can swim during red tide without serious risks, but it may cause symptoms such as skin irritation and a burning sensation in the eyes.
What causes red tides quizlet? ›Red tide is caused by Algal blooms- During which, algae becomes so numerous and it may deplete oxygen and emit toxins into the air. different species in the water causes a discoloration.
Is red tide an algae? ›In the ocean, microscopic forms of algae, known as dinoflagellates, can "bloom" into dense patches near the surface, often referred to as "red tides." Some of these harmful algal blooms (HABs) are dangerous, producing toxins that can kill marine organisms, taint shellfish, cause skin irritations, and even foul the air.
When did red tide start? ›Red tides were documented in the southern Gulf of Mexico as far back as the 1700s and along Florida's Gulf coast in the 1840s. Fish kills near Tampa Bay were even mentioned in the records of Spanish explorers in the 1500s.
What color is red tide? ›Red tides, explained. These toxic algal blooms, some deep red in color, trigger a tide of effects on animals and humans. Often deep red or brown in color, a typical red tide can be observed along a marine coast. A type of harmful algal bloom, red tides refer to toxic blooms of microscopic algae that occur worldwide.
Is red algae harmful to humans? ›
Red tides, blue-green algae, and cyanobacteria are examples of harmful algal blooms that can have severe impacts on human health, aquatic ecosystems, and the economy. Algal blooms can be toxic. Keep people and pets away from water that is green, scummy or smells bad.
Can you eat fish from red tide? ›The toxins that kill fish, brevetoxins, accrue in the animal's gut. When a fish is filleted, its internal organs are removed, thus eliminating any threat posed by the red tide. It's also important to remember never to eat any fish that have been recovered from a red tide, regardless of how they've been prepared.
Is red tide harmful to dogs? ›Yes, red tide is dangerous to animals (including humans and dogs). “The K. brevis produces brevetoxins, which is a neurogenic toxin, affecting the central nervous systems of fish and other vertebrates, causing death,” Dr. Mears said.
Where does red tide occur? ›Where do red tides occur? Red tides occur in coastal waters all over the world. In the United States, they are common along the Texas coast, and they occur almost every summer along the Gulf Coast of Florida. They're also common along the coast of California and in the Gulf of Maine.
What are algal blooms? ›What is a harmful algal bloom? A harmful algal bloom (HAB) occurs when toxin-producing algae grow excessively in a body of water. Algae are microscopic organisms that live in aquatic environments and use photosynthesis to produce energy from sunlight, just like plants.
What are some of the benefits of recycling and reclaiming materials in the waste stream of industrial processes? ›Not only does recycling and reclaiming materials in the waste stream have environmental benefits, it also has benefits because the material can be sold for a profit. It washes into surface water bodies. Scavengers consume it. It dries and becomes part of air pollution particulates.
Why can it be fatal to eat shellfish gathered during a red tide? ›What happens if toxic shellfish are consumed? Eating toxic shellfish can cause paralytic shellfish poisoning (PSP) in humans. PSP is caused by saxitoxin, which is produced by Alexandrium fundyense and is one of the most potent toxins known to scientists.
Where is red tide the worst? ›Beaches along Florida's central and southwest coast are most affected by red tide, including the beautiful beaches near Tampa Bay, Sarasota, Anna Maria Island, Sanibel and Captiva Island.
What is red tide biology? ›red tide, discoloration of sea water usually caused by dinoflagellates, during periodic blooms (or population increases). Toxic substances released by these organisms into the water may be lethal to fish and other marine life. Red tides occur worldwide in warm seas.