Algal Toxins and Wildlife Health

Science Center Objects

Harmful algal blooms (HABs) have the potential to harm fish and wildlife, domestic animals, livestock, and humans through toxin production or ecological disturbances such as oxygen depletion and blockage of sunlight.

To investigate the effects of algal toxins on wildlife, the USGS National Wildlife Health Center (NWHC) has examined over 300 dead animals collected during freshwater and marine HAB events since 2000. Varying levels of algal toxins were found in over 100 of these animals. In some cases, the history, clinical signs, and high toxin levels have allowed scientists to attribute mortality to algal toxicosis. Recent events have included Kittlitz’s murrelets (Brachyramphus brevirostris) in Alaska that died after consuming sand lance (Ammodytes hexapterus) high in saxitoxin (Shearn-Bochsler et al. 2014), green tree frogs (Hyla cinerea) in Texas with suspected brevetoxicosis in association with a red tide event (Buttke et al. 2018), and little brown bats (Myotis lucifugus carissima) in Utah found dead during a HAB event at a reservoir commonly used for recreation and as a source of municipal drinking water (Isidoro-Ayza et al. 2019). 

Common Murre on the water in Kachemak Bay, Alaska

A Common Murre on the water near its colony in Kachemak Bay, Alaska. (Credit: Sarah Schoen, U.S. Geological Survey. Public domain.)

In other cases, algal toxins have been detected in wildlife, but their contribution to mortality remains unclear. Part of the reason these detections have been difficult to interpret is that the toxic dose of many algal toxins in wildlife species is unknown and the microscopic lesions (if any) particularly in birds, have not been well described. To better understand the effects of these toxins the NWHC is conducting laboratory exposure trials to determine the lethal dose of toxin in birds and to examine the repeated exposure of waterfowl to sub-lethal toxin ingestion. In addition to exposure trials, NWHC is undergoing a retrospective review of previous detections of algal toxin from NWHC’s case archives to examine demographic, spatiotemporal, and diagnostic features associated with wildlife exposure to algal toxins.