Scientists studying red tide in Alaska are worried that climate change could awaken a sleeping giant.
A new study, led by scientists from the Woods Hole Oceanographic Institution and published in the Oct. 12 “Proceedings of the National Academy Science,” sampled the sea bed and surface waters in the Chukchi and Beaufort seas in 2018 and 2019 and mapped red tide cyst beds.
Researchers found two of the largest cyst fields in the world in the Chukchi Sea north of the Bering Strait and in the western Beaufort Sea near Point Barrow. The discovery stoked fears that rapidly warming and freshening waters in Arctic seas, likely driven by climate change, will cause these cyst fields to come out of dormancy, potentially affecting that region’s ecosystem and food web from herring to whales.
The University of Washington Polar Science Center reported that during the period from 1990 to 2020 summer waters north of the Bering Strait were 2 to 4 degrees Celsius warmer than in 1990 and stayed warm for a month and a half longer. The Gulf of Maine Research Institute said Gulf of Maine temperatures have been above average 92% of the time since 2010 — and 81 days during that time period qualified as being in a marine heat wave.
Peril from warming oceans
Warming seas and air temperatures have already hit some species hard. Young Atlantic puffins in the Gulf of Maine have had problems surviving after herring schools moved to cooler waters in recent years. Puffins in Alaska have also experienced mass die offs for similar reasons.
In 2019, the National Park Service documented the deaths of thousands of lesser shearwaters. It marked the fifth year in a row with big die-offs of birds due to starvation, as their prey fish species vanished with warming ocean temperatures. Thousands of Arctic terns were found dead in 2019 in southeast Alaska, blamed on saxotoxins produced by red tide algae.
In New England, where we eat shellfish like mussels and clams that accumulate toxins in their digestive system as they filter feed on Alexandrium catenella algae, the danger of paralytic shellfish poisoning is real and whole coastlines can be closed to shellfishing to protect humans.
The human diet is more focused on fish and marine mammals in Arctic Alaska. The toxin collects in those animals’ organs that are not generally eaten, said Woods Hole Oceanographic Institution senior scientist Don Anderson, and the danger of poisoning in humans is less acute. But researchers do worry that the expansion of red tide into ocean north of the Bering Strait could also ultimately affect the Arctic’s subsistence hunting and fishing that sustain many of the region’s small, remote villages.
“The risk to humans is fairly low compared to (the risk to) a whole ecosystem that is already struggling,” said Anderson, who also is the director of the U.S. National Office for Harmful Algal Blooms.
There are different types of red tides, caused by different algae. Some of these algae produce toxins that can kill fish, shellfish, marine mammals as big as whales, and birds. Alexandrium catenella algae, which are responsible for the red tides in both Alaska and New England, prefer temperatures in the 50 to 55 degree range and sea water that has freshwater mixed in.
What causes red tide?
Red tide blooms generally originate in cyst fields where algae spend the cold winter months on the ocean floor encased in an armored shell and emerge when temperatures are favorable in the spring. These algae have tails that propel them to the surface and they are dispersed by coastal currents. They become lethal as they are eaten and accumulate in the organs of the predator and work their way up the food chain.
The Gulf of Maine, specifically an area of ocean off mid-coast Maine, is one of the world’s most studied and largest red tide cyst fields. Salt Pond, a small tidal pond in Eastham’s Nauset Marsh, is a living laboratory with its own cyst bed, where scientists have rigorously studied the organism and technologies used to detect it.
Ironically, even though New England’s Gulf of Maine, like the Arctic seas of Alaska, is also among those areas warming faster than the rest of the world’s oceans, Anderson said our ocean may reach temperatures beyond what the Alexandrium bacteria can tolerate.
Although red tides are relatively well known in southeastern Alaska, it was thought the cold Arctic waters were unlikely to support a large bloom. But the WHOI study revealed that a warming atmosphere, combined with a severely diminished ice pack and warmer, fresher water flowing through the Bering Strait from the North Pacific Ocean, created conditions that were favorable for red tide blooms.
When it met the cold waters north of the Bering Strait, the red tide algae carried from southeastern Alaska formed cysts and dropped to the bottom creating gigantic cysts fields over time in an area that might never reach optimum. These cysts can remain dormant for decades and some cysts have been revived in a lab setting from bottom sediment that is over 100 years old.
Concerns of a red tide nursery
With warming seas, researchers are worried that the enormous cyst beds they discovered may turn from graveyard to nursery, and the amount of germinating red tide cells could double. Anderson said that moored automated monitoring stations like one deployed in the Gulf of Maine that sample water, count and identify cells, and broadcast results to researchers on shore, will be set up in the Bering Strait.
“It’s plenty warm, just as warm as the Gulf of Maine seed beds and we know how they function,” said Anderson, the study’s lead author. The research, done in collaboration with the National Oceanic and Atmospheric Administration and other researchers from the U.S., China and Japan and funded by NOAA’S Ecohab program, showed that it is likely that occasional red tide blooms north of the Bering Strait would become recurrent, large and dangerous.
Exactly how dangerous is the focus of the second part of the study.
“We know the risk of exposure is there,” said Kathi Lefebvre, a researcher at the NOAA Northwest Fisheries Science Center in Seattle, Washington. Lefebvre is in the final phase of a report on toxicity found across the Arctic Alaskan food web, from plankton to whales.
A network of local inhabitants in remote villages helped the research by collecting fecal samples from wildlife. Low level exposure is common to all animals sampled, she said.
“These animals are being exposed (to saxotoxins from red tide algae), but what we don’t know is whether they are high enough to cause health impacts,” Lefebvre said. Preliminary data seems to be suggesting the doses of toxins are not high enough to cause illness or death.
Part of the study is determining just how much is too much for each of the species. The goal is to link sampling of red tide algae cell counts in water to potential toxicity levels in animals and determine a possible level of harm.
“Under these bloom densities ... we see these impacts in marine mammals,” Lefebvre said. “When will conditions be such that it is high enough to kill marine mammals? That will be the problem. They (subsistence hunters) care about it because they are 100% reliant on these resources, like subsistence hunting for walrus and ice seals, and whaling.”
“The one thing I take from this study is that this is an organism moving north into waters where we normally thought were too cold,” Anderson said.
The difference between the Chukchi Sea in Arctic Alaska and the Gulf of Maine in New England is that here red tide is already established. As our waters get warmer, we won’t see an extension of red tide south, but instead it could move north.
“Labrador, Greenland, Iceland, that’s where this problem could be moving to,” Anderson said.