Alaska hide your mammals. Algal blooms are coming for you..

Harmful algal blooms are caused by proliferation of harmful algal species and during these blooms diatoms are responsible for the production of domoic acid (DA) and dinoflagellates are also responsible for the production of saxitoxin (STX). Both toxins are the causative agents of amnesic and paralytic shellfish poisoning. Trophic transfer of these algal toxins has various different transport vectors, however the accumulation of these toxins within benthic and pelagic invertebrates allows transfer of these toxins to top predators. The neurotoxic effects of these toxins on marine mammals have shown that exposure can interfere with diving and feeding behaviours as well as seizures and ataxia, leading to increased strandings. Change in environmental conditions and specifically sea surface temperature are extending the geographic distribution of harmful algal blooms and therefore understanding the range of where these toxins are present is important for identifying threats and potential impacts they would have on marine mammals.

Lefebvre et al, 2016 looked at the presence and concentration of DA and STX in Alaskan waters and whether they have the potential to impact marine mammals health within the Arctic marine environments. Varieties of samples (faeces, stomach content, urine, amniotic fluid, etc.) were collected from 905 Alaskan marine mammals across 13 species from south-eastern Gulf of Alaska to the eastern Beaufort Sea. The species tested were humpback whales (Megaptera novaeangliae), bowhead whales (Balaena mysticetus), beluga whales (Delphinapterus leucas), harbour porpoises (Phocoena phocoena), northern fur seals (Callorhinus ursinus), Steller sea lions (Eumetopias jubatus), harbour seals (Phoca vitulina), ringed seals (P. hispida), bearded seals (Erignathus barbatus), spotted seals (P. largha), ribbon seals (Histriophoca fasciata), Pacific walruses (Odobenus rosmarus), and northern sea otters (Enhydra lutra). Samples were instantly frozen and sent for algal toxin analysis. Algal toxins were quantified using enzyme-linked immunosorbent assay kits to quantify domoic acid (DA) and saxitoxin (STX) concentrations. There were slight modifications to the protocol to allow testing of marine mammal samples.

Results found that algal toxins were detected in at least one animal from all 13 species sampled. DA concentrations were detected in all 13 species and within 188 individuals, with the highest concentration detected being 6457ng/g, which was sampled from a 15-year-old female walrus from northern Bering Sea. DA was most prevalent in bowhead whales with 68% of individuals having detectable concentrations, and the least prevalent was spotted seals with only 3%. DA was also detected in 3 fetuses. STX was detected in 10 species and in 107 individuals, with the highest concentration detected being 240ng/g, which was sampled from a 21-year-old male walrus, which was also from the northern Bering Sea. STX has the highest prevalence in humpback whales with 50% and the lowest found in spotted seals with 1%. 46 individuals contained detectable concentrations of both DA and STX and both toxins were detected in marine mammals throughout the entire study area.

This study is important in showing that algal toxins are already present along the Alaskan coast and in larger concentrations than previously recognised. The data found in this study suggests that Alaskan marine mammals may be experiencing near toxic levels of DA concentrations already as the DA concentrations found in the Alaskan marine mammals were very similar to the concentration found in Californian sea lions experiencing DA toxicosis. This is therefore an important study to highlight the increasing health risks Alaskan marine mammals may face if the geographic range and toxicity of HABs continues to increase with rise in temperature. More work could be done to look at the direct impact DA and STX have on the behaviour of marine mammals as most samples in this study were dead when sampled and their death may have been due to something other than the toxicosis. It would also be interesting to see which species are more vulnerable to the toxins.

Lefebvre, Kathi A., et al. "Prevalence of algal toxins in Alaskan marine mammals foraging in a changing arctic and subarctic environment." Harmful Algae 55 (2016): 13-24.