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,