Unraveling the Mysteries of Red Tides
Courtney Cocilova, Ph.D. and Sarah L. Milton, Ph.D.
Department of Biological Sciences, Florida Atlantic University
Harmful algal blooms (commonly called Red Tides) are increasing in duration and frequency around the world. In Florida, they occur almost annually in the Gulf of Mexico but also occur in other enclosed bays such as the Chesapeake Bay, Gulf of Arabia, and Moreton Bay in Australia. These algal blooms are called Red Tides because of the red colored cells of some algal species, while others may be brown, green, or colorless. When excess amounts of nutrients are present in the water resulting from agricultural run-off, sewage, and/or fertilizers, populations of these microscopic algae, known as dinoflagellates, can grow out of control.
Millipede? Centipede? Nope, it’s the chemical composition of Brevetoxin, a lipid-soluble compound that easily crosses cell membranes to affect nerve and muscle cells.
This rapid algal overgrowth can have many damaging effects on wildlife as well as affect human health. Dinoflagellates have the ability to create algal mats which shade out sea grasses and deplete the area of oxygen, while other blooms are considered to be “harmful” because they release toxic chemicals into the water. The non-toxic HABs known as brown tides may be so extensive that they block sunlight and damage seagrass beds. In the Indian River Lagoon (IRL), a large estuary on the east coast of Florida, Brown Tides in 2009-2011 caused the loss of nearly 32,000 acres of seagrass, with additional losses in 2012. The end result was the death of approximately 60% of the seagrass cover in the IRL. Blooms can also occur in freshwater, such as the large cyanobacterial bloom that occurred in Lake Erie in 2014; it was so large that city of Toledo residents were unable to drink or cook with the water for several days.
The dinoflagellate Karenia brevis. Photo: Fl. Fish and Wildlife Conservation Commission
Many readers may have heard of such conditions as Paralytic Shellfish Poisoning (PSP) and Neurotoxic Shellfish Poisoning (NSP),
in which people who have consumed shellfish experience gastrointestinal upset and neurological symptoms such as headache, muscle weakness, and vertigo. Severe cases can result in respiratory failure and death from paralysis. PSP is caused by one algal toxin, called saxitoxin, which is produced by the Alexandrium family of dinoflagellates, while the brevetoxins, produced by the dinoflagellate Karenia brevis, cause NSP. Other toxins include the ciguatoxins, which accumulate in fish, and domoic acid, produced by the Pseudonitzschia family. These toxins all alter nerve and muscle function by changing the flow of ions across cell membranes, leading to either reduced function or overexcitability. Domoic acid, for example, affects the part of the brain (the hippocampus) concerned with learning and memory, and causes amnesic shellfish poisoning. Besides gastrointestinal and neurological problems, toxins are released into the air from ocean waves and can cause respiratory effects in people on nearby beaches: itchy eyes, coughing, and wheezing, particularly in asthmatics. Fisheries may also be closed when a bloom warning is in effect if toxin levels are dangerous. In 2015, a large Pseudonitzschia bloom off the west coast of the United States and Canada closed the razor clam harvest, causing an estimated $9.2 million in lost income while also delaying opening of the Dungeness crab fishery.

Human activities contribute to a higher concentration of nutrients in the environment, which is the primary root of the problem and the reason dinoflagellates can reproduce in such large numbers. Blooms are getting worse and have been lasting longer as well as occurring closer to shore. The 2015 Pseudonitzschia bloom was the largest in at least the past 15 years, for example, extending from the Channel
Islands of California as far north as Alaska. In addition to their health impacts on humans, algal blooms can be devastating to marine animals that inhabit and/or nest on the nearby beaches. Large numbers of marine animal deaths have been directly linked to dinoflagellate blooms and many
animals have also been found stranded. Affected animals include many fish, seabirds such as cormorants and pelicans, dolphins, manatees, and several species of sea turtles. In the spring of 2015, the deaths of hundreds of diamondback terrapins on Long Island (NY) and in Delaware were similarly associated with a toxic algal bloom. Some of the common symptoms associated with toxin exposure include muscle twitching, uncoordinated movements, swimming in circles, unresponsiveness, and even coma. In 2007, 79 sea lions in California died after consuming fish that contained high levels of domoic acid, and more animals are dying this spring. In sea lions, domoic acid triggers seizures; those that survive may suffer permanent brain damage. Florida wildlife veterinarians are seeing more turtles with domoic acid exposure lately as well. At lower, non-lethal concentrations, toxins can still target and impair the immune system, so that even if the exposure does not result in immediate death, animals may be more susceptible to disease or to additional stressors. Bioaccumulation (where levels of toxin build up over time in one animal) and biomagnification (where animals higher up the food chain consume larger doses than prey species) are both likely to increase the harmful effects marine animals face during blooms, as we are seeing with contaminated anchovies and California sea lions.

Close to home, the Gulf of Mexico is home to the particular dinoflagellate species, Karenia brevis, which specifically releases brevetoxins.
The term Florida red tide is commonly used to distinguish the Gulf of Mexico red tide blooms from other blooms. A strong outbreak of K. brevis in 2005-2006 off the west coast of Florida led to 318 documented sea turtle strandings, with more than 90% of both live and dead stranded animals testing positive for the toxin produced by the algae. One hundered seven dolphin mortalities were associated with a 2004 red tide, while following an unusual mortality event in manatees in 2013, 168 out of 276 animals tested positive for the toxin. Brevetoxins directly affect the nerves and muscles of animals making it difficult for them to swim, capture prey or graze, or get out of an area where the toxin is present. While humans that ingest contaminated shellfish may get neurotoxic shellfish poisoning, it is rarely lethal; marine animals like sea turtles can be exposed to much higher levels of toxin and may eventually die; while we may get sick after eating a meal of contaminated clams, for instance, for wildlife, contaminated prey may make up their entire diet. Animals that are alive but unable to swim and dive properly often strand on the beach or are found floating in the water and are taken to rehabilitation facilities, where they can be offered supportive care. Our work at Florida Atlantic University, supported by grants from the National Oceanographic and Atmospheric Administration as well as the Friends of Gumbo Limbo and National Save The Sea Turtle Foundation, sought to develop treatments to help sea turtles recover from toxin exposure.

Seven species of sea turtles inhabit our oceans worldwide and nearly all are listed as either threatened or endangered. These animals are faced with many threats including climate change, fisheries bycatch, light and ocean pollution, habitat destruction and red tides. Sea turtles are very vulnerable to red tides since they feed on seagrass beds that may be covered in algae, or on fish and small shellfish that in turn consume the toxins when they are feeding. However, there is no way to know how much of the toxin sea turtles or other marine animals are exposed to in the wild or how long they spend navigating and foraging in an area where a red tide is occurring, nor do we know what organ systems are most affected or how badly. It isn’t possible to answer these questions for sea turtles experimentally due to their status as threatened/ endangered and so treatment options are difficult to explore. We have thus lacked firm knowledge of the best ways to treat sick sea turtles and help them recuperate from exposure to toxins. The primary treatment for animals in rehabilitation which have been exposed to toxins is supportive care while we wait for the toxins to naturally clear out of their bodies.

The Red Tide research we conducted at Florida Atlantic University focused on the impacts of Red Tides on endangered sea turtles by using common and abundant freshwater turtles as alternative models for marine turtles. With the development of model organisms that have been used in research for decades,
it was possible to explore more in depth the effects of brevetoxin. Little was known about brevetoxin accumulation, uptake, tissue distribution and how long it takes to clear out of the system in sea turtles. By using a model species, like the freshwater turtles, we were able to address these questions. Controlled laboratory results have shown that the freshwater turtles are highly resistant to brevetoxin compared to mammals, but possess the same symptoms as sea turtles which come into rehabilitation facilities suffering from exposure, therefore making them a good model species. We showed that exposure to the toxin affected all of the organ systems like the brain, heart, and muscles, and that it is cleared out primarily by liver detoxification and excretion with the feces.
Diamondback terrapin (Malaclemys terrapin). Hundreds of terrapins similar to this one were killed by toxic algae in NY and Delaware in the spring of 2015. Photo credit S. Milton.
Our research has led to the successful development of a potential treatment for brevetoxin exposure, where a lipid compound is introduced into the animal after toxin exposure. The lipids bind to the toxin; by pulling it out of cells the symptoms of toxin exposure are rapidly ameliorated, and the toxin also passes out of the system more quickly so that the sick animal is able to recover.
Sea turtle rehabilitation facilities will soon be testing this treatment in sea turtles exposed to the toxin, as Florida K. brevis blooms occur primarily in the late summer and early fall when the waters are warmer. This treatment will help speed up the recovery not only for sea turtles who come into rehabilitation facilities, but may also help other marine life affected by Red Tides.

While designing treatment plans to help animals survive toxin exposure is one way of addressing the problem of red tides, however, a far better solution would be to address the issue of nutrient overload in our water systems. For homeowners, this means careful application of fertilizers; in cities, reduced sewage overflow. For agriculture, better capture and cleaning of contaminated waters before they are released into our bays and oceans would improve water quality. Minimizing nutrient overload will help protect the
FAU graduate Dr. Courtney Cocilova examines a freshwater turtle exposed to brevetoxin.
environment and potentially reduce the extent, frequency, and duration of Red Tides to the benefit of both human and animal life. Increased development of monitoring methods and field-related tools for early detection of toxins in aquat- ic systems is currently an area of investigation, and would also reduce wildlife deaths. Besides pollution, increasing water temperatures contribute to algal reproduction; so as the earth’s waters continue to warm, algal blooms are only going to continue to grow in size and in frequency to the detriment of our ecosystems in Florida and elsewhere.
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