Saxitoxin detected in regional clam
By Diana Haecker
A six-inch butter clam harvested on August 28 three miles north of Savoonga tested positive for saxitoxins, or paralytic shellfish poison, Norton Sound Health Corporation Environmental Coordinator Emma Pate said.
The clam was sent to the Southeast Alaska Tribal Ocean Research Laboratory, or SEATOR, in Sitka for testing after researchers have alerted the region about very high levels of Alexandrium catenella phytoplankton cells in regional waters this summer. Alexandrium is an algae that can produce saxitoxins which in turn can cause paralytic shellfish poisoning in people and animals after eating clams, mussels or other shellfish feeding on those algae.
The clam itself showed high levels of saxitoxin present: it had 450 micrograms of toxin per 100 gram of body tissue. The Food and Drug Administration’s safety limit is at 80 micrograms/100 g. Pate, via the SEATOR lab, on Sept. 23 issued a paralytic shellfish toxin advisory to Savoonga and Gambell.
Pate said that more samples have been collected and are currently awaiting to be tested.
SEATOR is a network of 17 tribes in the Gulf of Alaska, collecting phytoplankton and shellfish samples from southeast Alaska beaches to track harmful algal blooms and marine biotoxins. Shellfish poisoning is of great concern in southern parts of Alaska, and with warming waters triggering harmful algal blooms in northern parts of Alaska, this becomes a novel concern for this region, too. Norton Sound Health Corporation’s Office of Environmental Health had already started a program to test the waters for harmful algal cells in order to build a baseline data base for the region. The effort was accelerated by this summer’s news of very high Alexandrium cell counts in regional waters, detected by a team of researchers from the Woods Hole Oceanographic Institute on research cruises to specifically research harmful algal blooms in the northern Bering Sea and Chukchi Sea.
The evidence of the clam with saxitoxins over five times the level for safe consumption is bringing up the question of a warning system that would alert subsistence users when high levels of harmful algal blooms result in saxitoxin presence in subsistence species such as clams and mussels. This summer, the Woods Hole researchers alerted Norton Sound of their findings and NSHC issued advisories to coastal communities. But it was and still isn’t know how toxic the waters with the off-the-charts cell count of Alexandrium were. Until the clam was analyzed, there was also no data on toxicity of shellfish or other species swimming and feeding in these waters.
Subsistence foods falls outside the regulatory framework for the state of Alaska. The state doesn’t recognize subsistence as a food security measure and views it as a “recreational activity.” Commercial shellfish harvests are being tested but recreationally harvested species are not. As marine mammals often consume shellfish that may be containing saxitoxins, and are in turn a hunted for subsistence, the question comes up how saxitoxins can affect marine mammals.
NOAA research biologist Kathi Lefebvre started the Wildlife Algal-Toxins Research and Response Network over a decade ago to measure algal toxin presence in stranded and subsistence harvested marine mammals. “Our goal is to determine the impact of these toxins on marine mammal health and help to determine the cause of death of stranded animals. WARRN West is a wildlife health program and does not address human health issues,” she said.
Her lab is analyzing clams, worms and krill to answer the question how long toxins remain in these Arctic organisms after an algal bloom. “We don’t have the answer right now. Unfortunately, we don’t know when the danger is over. There are toxins in algal cysts (seeds for the algae). Clams can eat these cysts and may remain toxic even when a bloom ends if they are feeding on toxic cysts on the seafloor,” she said.
The regulatory agency responsible for human health protections regarding seafood is the Alaska Department of Environmental Conservation, Division of Environmental Health, Food Safety and Sanitation Program.
However, since the state doesn’t test subsistence species, Lefebvre’s research is of interest to the region even though her lab cannot give human consumption advice. She samples stranded marine mammals from this region down to the California coast and as harmful algal blooms become a bigger issue, her focus is on Arctic wildlife. Lefebvre is taking samples to track where harmful algal blooms are, how big they are, how toxic they are during research cruises. They are also taking food web samples of clams, worms, fish, krill and measuring toxins in those organisms. “Our overall goal is to determine how toxic the food web gets under different blooms conditions and to develop a model to tell us when we expect toxin levels to be dangerously high and impact wildlife health with an emphasis on marine mammals,” she said. “We don’t know for sure how the regulatory limit for humans compares to walruses. We do know that walruses can be impacted by PSP toxins and that they are likely receiving doses of toxin at times during blooms in the Arctic that are impacting their health.”
Lefebvre is working with Gambell and Savoonga hunters to sample subsistence harvested walruses. “We do not yet know what level of toxins will kill a walrus, but we will get that answer as our study continues,” she said.
She said that the high Alexandrium cell counts from this season are alarming and indicate that there will be lots of toxin in the food web. “We are currently analyzing clams from the first leg of the Norseman cruise taken during high cell counts this season. We are finding high toxin levels in clams again this season. This will present a risk to walruses that feed on these clams. This also increases the risks of there being highly toxic clams in the guts of walruses and that is a concern for human consumers that eat clams directly from the guts of walruses.”
Lefebvre and her team also study where toxins go in marine mammals’ bodies. “We are using the walrus as a model for marine mammals. We are getting several sample types from each walrus —feces, blubber, muscle, liver, kidney, heart. We are analyzing the toxin levels in all of those samples for each animal. The goal is to see if toxin levels reach harmful levels in any of those marine mammal tissues during toxic blooms. We do not expect toxin levels to reach dangerous levels in muscle or blubber.”
In a 2019 study, Lefebvre also found that bowhead whales were consuming much lower doses of toxin from eating krill than walruses get from eating clams. “We don’t think that toxin exposure to bowheads was high enough to cause health impacts to the whales,” she noted.