In the summer of 2015, a massive toxic bloom of the marine diatom Pseudo-nitzschia, stretching from central California to the Alaska Peninsula, resulted in significant impacts to coastal resources and marine life. NOAA worked closely with federal, state, tribal, academic, and other partners to respond to this unprecedented harmful algal bloom (HAB).
Blooms of Pseudo-nitzschia occur annually at "hot spots" along the U.S. West Coast and produce a potent neurotoxin, domoic acid, which can accumulate in shellfish, other invertebrates, and sometimes fish, leading to illness and death in a variety of seabirds and marine mammals. Human consumption of shellfish contaminated with domoic acid can result in Amnesic Shellfish Poisoning, which can be life threatening but is also rare. For finfish like salmon, tuna, and pollock, levels in edible portions of the animal are well below levels of concern for human consumption. Greatest human risk is from recreationally-harvested shellfish; commercial shellfish and finfish are closely monitored and safe to eat. Each state maintains public websites indicating where harvesting shellfish can be safely conducted.
This particular bloom was detected in early May 2015, when Washington closed its scheduled razor clam digs on coastal beaches. Scientists quickly recognized that the bloom extended from California's Channel Islands to as far north as Alaska. The bloom was the largest and longest-lasting in at least the past 15 years. Concentrations of domoic acid in seawater, some forage fish, and crab samples were among the highest ever reported for this region. By mid-May, domoic acid concentrations in Monterey Bay, California, were 10 to 30 times the level that would be considered high for a normal Pseudo-nitzschia bloom. Other HAB toxins were also detected on the West Coast. Shellfish closures in Puget Sound protected consumers from Paralytic Shellfish Poisoning and Diarrhetic Shellfish Poisoning.
Impacts to coastal resources and marine life included shellfish and Dungeness crab harvesting closures in multiple states, anchovy and sardine fishery closures in some areas of California, and sea lion strandings in California and Washington. Other marine mammal and bird mortalities were reported in multiple states, but domoic acid was not confirmed as the cause. On August 20, 2015, NOAA declared an Unusual Mortality Event for large whales in the Western Gulf of Alaska. During the bloom, scientists recorded the mortality of 30 large whales. The HAB event was suspected of playing a role in the deaths of these whales given the noted warmer than usual ocean temperatures in the Gulf of Alaska and the algal bloom documented in neighboring areas (Kachemak Bay). However, there was no conclusive evidence at this date linking the whale deaths to HAB toxins.
Nearly one year since the start of the bloom, most shellfish and fish harvesting have reopened, but Dungeness crab and razor clam harvesting in some parts of northern California remain closed due to some persistent elevated domoic acid levels in the region. The full economic impact of these closures is still being calculated.
While researchers are investigating the exact causes of the severity and early onset of the bloom, unusually warm surface water in the Pacific is considered a factor. First reported along the West Coast in the 1990s, Pseudo-nitzschia blooms have also been observed off the U.S. East Coast and in the Gulf of Mexico.
At the outset of this event, NOAA already had multiple HAB projects underway along the West Coast. NOAA responded quickly after the bloom was detected to determine its geographic extent and causes. Specific efforts by NOAA include: