Climate Extreme Seeds a New Domoic Acid Hotspot on the US West Coast

Vera L Trainer,Nicolaus G Adams,Matthew V Hunter,Raphael M Kudela,Ryan M Mccabe

doi:10.3389/fclim.2020.571836

Abstract

A heatwave that blanketed the northeast Pacific Ocean in 2013–2015 had severe impacts on the marine ecosystem through altered species composition and survival. A direct result of this marine heatwave was a sustained, record-setting harmful algal bloom (HAB), caused by the toxigenic diatom, Pseudo-nitzschia, that led to an unprecedented delay in harvest opportunity for commercial Dungeness crab (Metacarcinus magister) and closure of other recreational, commercial and tribal shellfish harvest, including razor clams. Samples collected during a cruise in summer 2015, showed the appearance of a highly toxic “hotspot” between Cape Mendocino, CA and Cape Blanco, OR that was observed again during cruises in the summers of 2016–2018. The transport of toxic cells from this retentive site northward during wind relaxations or reversals associated with storms resulted in economically debilitating delay or closure of Dungeness crab harvest in both northern California and Oregon in 2015–2019. Analyses of historic large-scale Pseudo-nitzschia HABs have shown that these events occur during warm periods such as El Niño, positive phases of the Pacific Decadal Oscillation, or the record-setting marine heatwave. In order to reduce the impacts of large-scale HABs along the west coast of North America, early warning systems have been developed to forewarn coastal managers. These early warning systems include the Pacific Northwest and California HAB Bulletins, both of which have documented elevated domoic acid and increased risk associated with the northern California hotspot. These early warnings enable mitigative actions such as selective opening of safe harvest zones, increased harvest limits during low risk periods, and early harvest in anticipation of impending HAB events. The aims of this study are to show trends in nearshore domoic acid along the US west coast in recent years, including the recent establishment of a new seed bed of highly-toxic Pseudo-nitzschia, and to explore how early warning systems are a useful tool to mitigate the human and environmental health and economic impacts associated with harmful algal blooms.

Highlights

The effects of climate change on marine ecosystems will be long lasting
Toxigenic Pseudo-nitzschia blooms are known to initiate in highly retentive regions, designated as harmful algal bloom (HAB) “hotspots” along the west coast, including the Juan de Fuca eddy, Heceta Bank, Monterey Bay, and Point Conception (Trainer et al, 2001, 2012)
The warm water anomaly was found to be a source of Pseudo-nitzschia that were delivered to the coast after a series of spring storms, where these cells grew rapidly to bloom proportions when fueled by nutrients from upwelled waters close to shore (McCabe et al, 2016; Trainer et al, 2020)

Summary

Introduction

The effects of climate change on marine ecosystems will be long lasting. The impacts of climate change on marine biota, including the shifting range of marine species to higher latitudes, have decreased food security, and enhanced the decline of coral reefs by 70–90% at 1.5◦C warming (IPCC, 2018). The International Panel on Climate Change report documented a high confidence of increased frequency and range of harmful algal blooms (HAB) in coastal areas since the 1980s, attributed partly to the effects of ocean warming and marine heatwaves (Collins et al, 2019). The 2013–2015 marine heatwave that caused large-scale marine ecosystem impacts in the northeast Pacific was five times more likely to occur due to anthropogenic forcing over natural variability alone. This was determined through fraction of attributable risk analysis which compared observed trends and anomalies with model predictions (Weller et al, 2015; Di Lorenzo and Mantua, 2016) to assess the probability of extreme events occurring with and without anthropogenic influences (Stott et al, 2004). The toxin, domoic acid (DA), produced by this diatom, accumulated in shellfish, resulting in an unprecedented delay in harvest opportunity for the commercial Dungeness crab (Metacarcinus magister) and closure of other recreational, commercial and tribal shellfish harvest (McCabe et al, 2016; McKibben et al, 2017)

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