New research indicates that climate change might be causing longer and more frequent gestations of toxic algae along Canada's Pacific Coast and into Alaska. These algal blooms, almost unheard of two decades ago, can be deadly for marine life and have been found to be the root cause of close to half of all unusual marine mammal deaths in the past 20 years.
A common phenomenon in tropical and more temperate regions, algal blooms occur when some species of phytoplankton grow rapidly under favorable conditions. When populations of certain algae are at particularly high intensities, the blooms are unmistakeably visible in green, yellow, red, or brown swaths that blanket the saltwater surface - sometimes massive enough to be seen from space.
"What really surprised us was finding these toxins so widespread in Alaska, far north of where they have been previously documented in marine mammals," said Kathi Lefebvre, a biologist for the U.S.-based National Oceanic and Atmospheric Administration and author of the recent research study on the toxic algae.
Between 2009 and 2013, Lefebvre and her research team studied samples from more than 900 Alaskan mammals, 13 species in total, including seals, walruses, sea otters, and whales, looking for evidence of domoic acid and saxotoxin, two common and potentially deadly algae-produced neurotoxins.
Domoic acid causes amnesic shellfish poisoning in humans, and in marine mammals, it can cause seizures and even death. The most well-known case of domoic acid poisoning in marine mammals was 1998, when more than 400 California sea lions perished along the central California coast.
Saxitoxin is a highly potent that can paralyze the respiratory system by blocking sodium channels, preventing the circulation of nerve impulses.
Lefebvre's team discovered evidence of both toxins present throughout the northern Pacific waters. Domoic acid was detected in all 13 species and saxitoxin in 10 of the 13 species. "This shows that algal toxins are present in northern food webs at high enough levels to be detected in marine mammals," Lefebvre explained.
Domoic acid was detected in two-thirds of the bowhead whales and harbor seals tested. Saxitoxin was found in half of the humpback whales and in one-third of the bowhead whales. Evidence of both toxins were present in 46 individuals, and the impact of combined exposure remains unknown.
More research will be needed to better understand the long-term trends of algal blooms, as well as to learn how the toxins move through the food chain. The linkages between higher toxin levels and climate chains also need to be further explored.
"This is something we need to pay attention to and it could become a bigger issue," Lefebvre concluded.
