Harmful algal blooms, or HABs, are becoming increasingly prevalent around the world as warm temperatures and high nutrient loads result in the perfect conditions for algal propagation. Dr. Sarah Milton with Florida Atlantic University has been examining the effects of HABs on common freshwater turtles in conjunction with efforts to save endangered sea turtle populations. Her research has focused on brevetoxins, which are produced by dinoflagellates; these algae are most commonly found in marine environments, which makes them a good focus in attempts to treat sea turtles, but they can also be found in freshwater conditions.
HABs can be harmful to aquatic life in various ways, not only due to the production of various toxins but also due to the massive decrease in dissolved oxygen which can occur near algal blooms. Dr. Milton points out to a Mongabay interviewer, “in Florida, the Indian River Lagoon estuary has very high nutrient loads from agricultural runoff, and the green turtles there have a high incidence of papilloma viral disease. In a pristine area nearby, turtles have zero disease.” While fibropapillomatosis, the turtle disease to which Dr. Milton is referring, is a tumor-producing viral disease, toxins produced by HABs are suspected to be connected to the condition. The variety of problems which HABs can cause sea turtles means that helping them survive the blooms is a challenging topic.
While there is some knowledge of the effect of brevetoxins on mammals, almost nothing was known regarding the effects of this class of toxins on turtles before Dr. Milton’s research. Green turtles (as well as other turtle species) have an incredible capacity to survive in anoxic conditions, sometimes for months at a time. This is part of the reason Dr. Milton chose them as a subject of her research. She believes that the turtles’ cellular capacity to continue function despite the influx of new oxygen is somehow connected to their ability to cope with toxins produced by HABs. Initially, sea turtles brought in for rehabilitation after massive HABs were thought to be showing symptoms of exposure to relatively small amounts of toxin. However, Dr. Milton’s research shows that turtles are actually incredibly resistant to brevetoxin-3, even more so that mammals which were previously exposed to the toxin. This is surprising, since the faster metabolic rates present in mammals means that they are typically faster at metabolizing foreign substances. The affected turtles brought in for rehabilitation, therefore, were likely to be exposed to extremely high concentrations of the toxin and for long periods of time. Dr. Milton suspects that the ability to stay deep underwater for long periods of time may be a critical aspect of the turtles’ resistance to HAB-produced toxins.
The capacity of these turtles to survive anoxic conditions, and their relative resistance to the effects of brevetoxins means that their cellular processes are a prime target for study as researchers attempt to find ways to mitigate the detrimental consequences of HABs. Thanks to Dr. Milton’s research, we now understand that, like mammals, the harmful effects of brevetoxin-3 on turtles are due to the holding open of sodium channels which results in cellular depolarization and the skewing of appropriate ion concentrations. While it isn’t yet clear why turtles are less susceptible to these effects than mammals, this research holds tremendous potential to help save aquatic species from the effects of HABs. Another potential application of this research involves the incredible ability of turtles’ cells to survive without new oxygen for extremely long periods. If the biochemical mechanisms enabling survival without regular influx of oxygen can be better understood, researchers and medical professionals could potentially use that knowledge to better treat individuals who have suffered a stroke, heart attack, or other condition involving anoxic cellular conditions.