Monitoring the Damage in the Heat Wave’s Wake

by Samantha Larson, University of Washington
September 15, 2022

In June 2021, the peak of an unprecedented heat wave coincided with extremely low tides in the Salish Sea, wreaking havoc on intertidal ecosystems. As a “heat dome” settled above the Pacific Northwest for several days and the temperatures climbed well above 100 degrees Fahrenheit, many scientists, resource managers and members of the public reported significant numbers of dead and dying shellfish on intertidal beaches throughout the region. Species such as cockles; Olympia and Pacific oysters; and varnish, butter, and native littleneck clams — normally buried out of sight —popped to the surface in large numbers. Surfaced clams were observed to be gaping, a sign of stress, or had already died from the effects of the heat. Some Pacific and Olympia oysters initially appeared to survive the heat but died in subsequent days, perhaps weakened by the extreme temperatures and unable to recover.

These observations raised alarm among shellfish growers and marine ecologists, especially given the ecological, cultural and commercial importance of these species. “This is possibly the first documented shellfish mortality event of this magnitude in modern times,” says Teri King, aquaculture and marine water quality specialist at Washington Sea Grant. “In some places, the effect is similar to a forest fire that has swept through the intertidal at the peak of the heat each day, for six days, killing much in its path.” The aftermath of the heat wave presented a critical opportunity to document and understand these impacts. Given this, WSG stepped in with rapid funding to support two regionwide surveys. The results of one of these studies were published in the journal Ecology in June 2022.

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