Oceanographic conditions are kind of different but also kind of the same this year compared to last year when we had a catastrophic Dungeness Crab closure, so it is only half a surprise that we are seeing a resurgence of domoic acid in the benthic environment. El Niño conditions were all but gone by summer 2016, but there has been something of a return of “blob”-like warming in surface waters off the coast. Some atmospheric signals are different from what was occurring during the Pacific Warm Anomaly of 2013-2016. Nonetheless, anomalous warming persists in some places, particularly the more northern parts of the California Current. This may explain the present isolation of the newest domoic acid problem to the North Coast (Humboldt Co. to Pt. Reyes). The California Harmful Algae Risk Mapping System (C-HARM) predicted high DA production along this stretch of coastline throughout September and October, which is consistent with a subsequent response in the benthic community (where crabs live) in November and December. The restriction of fishing in the Sonoma Co. region is dire news for crabbers barely recovering from last year’s closure and may disproportionately affect small boaters. The California Department of Public Health is bound to safeguarding the public from contaminated shellfish. The 30 ppm threshold is the best knowledge we have from mouse studies approved by the FDA, and if anything, other studies suggest we may not be conservative enough,1 particularly for human populations that are chronically exposed to DA due to frequent shellfish consumption.
But let’s get back to the unusual conditions spanning the Pacific, and the world, for the last couple years. It turns out these high DA events, if linked to warm conditions as suggested by a recent publication,2 are surprisingly connected to conditions occurring right now in the Arctic. A lot of attention at the North Pacific Marine Science Organization (PICES) meeting that just took place in San Diego was on the origin and ecosystem response of the Pacific Warm Anomaly, and it seems that there’s strong evidence to suggest that the “blob” is a result of melting sea ice in the Arctic.3 The North Pacific Oscillation was much bigger than usual because of the extremely warm sea surface temperatures at the Equator and low sea ice concentration in the Arcitc. This is a well-known pattern that often leads to unusual circulation in the atmosphere at high latitudes in the Northern Hemisphere. Daniel Swain discusses some of the atmospheric phenomena that link Arctic warming to mid-latitude regions in his discussion of the shocking Arctic heat wave over the last couple months. What this means for algal blooms in central to northern California is that persistent warm water in conjunction with fall pulses of upwelling is likely supporting pulses of growth of Pseudo-nitzschia and subsequent domoic acid production in the water column.