This past year marks the successful completion of my dissertation research on bottlenose dolphin susceptibility to harmful algal blooms (HABs), otherwise known as red tides. Over the past five years, through collaboration with the Sarasota Dolphin Research Program and NOAA Fisheries, I have used genetic techniques to investigate apparent differences in red tide resistance among bottlenose dolphins from central-west Florida and the Florida Panhandle.
Red tides in the Gulf of Mexico refer to naturally occurring dense blooms of the dinoflagellate algae, Karenia brevis, which produce neurotoxins. Exposure to these toxins can be lethal to fish, sea birds, sea turtles, and marine mammals, and can cause illness in humans. Several unusual mortality events (UMEs) of dolphins in Florida have been attributed to red tides. The goal of my research was to investigate if dolphins that have been frequently exposed to red tides historically have evolved resistance to the algal toxins. To test this hypothesis, I compared genetic variation between dolphins that died due to red tides and dolphins that survived red tide exposure, looking for a genetic signal that was more commonly observed in one group over the other. I included dolphins from both estuarine and coastal populations of bottlenose dolphins in central-west Florida (including Sarasota Bay) and the Florida Panhandle (see map).
I found that the frequency of some genetic markers varied significantly between live and dead dolphins, suggesting there may be some genetic basis to red tide resistance. The significant genetic markers were found within the dolphin genome nearby to genes involved in immune, nervous, and detoxification systems. A closer look at dolphin sodium channel genes, which encode the biological binding site of the toxin, revealed no significant differences. Unlike other neurotoxin-resistant systems (e.g., garter snakes that prey on toxic newts and clams exposed to HABs in New England), bottlenose dolphins have not adapted to red tide exposure via adaptations to the toxin binding site. Instead, the dolphin immune system, particularly the major histocompatibility complex, may play a previously undescribed role in red tide resistance. Overall, I conclude that genetics is likely one of several factors that influence the susceptibility of individual bottlenose dolphins to red tide exposure.
This research was supported by the Duke University Marine Lab, the American Fisheries Society, the PADI Foundation, and a Katherine Goodman Stern Fellowship. Samples were generously provided by the NOAA Fisheries SEFSC DNA Archives and the Sarasota Dolphin Research Program.
This article was published on page 15 in the November 2014 issue of Nicks n Notches