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Trophic Transfer of Domoic Acid in Food Webs of the Future Greenhouse Coastal Ocean Website

Principal Investigator(s):
David A. Hutchins - University of Southern California
Feixue Fu - University of Southern California
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Associate Investigator(s):
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Objectives:
We propose to measure the effects of warming and ocean acidification on bio-concentration of the harmful algal toxin domoic acid in local marine food webs. Our recent Sea Grant-supported work demonstrates that both elevated CO2 (ocean acidification) and sea surface warming can act to greatly increase the cellular toxin content of the diatom Pseudo-nitzschia, which annually forms large, environmentally and economically destructive blooms in our region. It is presently unknown however whether this global change-enhanced cellular toxicity will result in greater food chain bio-accumulation of this neurotoxin, starting with the secondary consumers that act as the main vectors to higher trophic levels. Our project will quantitatively evaluate how domoic acid is taken up during grazing under simulated future “greenhouse” conditions by economically important West Coast aquaculture species including larval and adult oysters and mussels, as well as in zooplankton such as copepods that serve as toxin conduits to wild-harvested finfish and squid. Our goal is to determine how warming and ocean acidification will affect the accumulation of domoic acid in economically and environmentally significant zooplankton and shellfish of the Southern California region.

Methodology:
We will apply established techniques for measuring assimilation and depuration of ingested contaminants in zooplankton and bivalves, in combination with ocean acidification and warming manipulative experimental methods and HPLC determinations of domoic acid in prey and grazers. Meroplanktonic larvae (oysters) and holozooplankton (copepods) as well as adult bivalves (oysters and mussels) will be fed Pseudo-nitzschia cells in which domoic acid levels have been manipulated by growing them under high CO2 and/or high temperature conditions (“future” highly toxic cells), or under present day CO2 and/or temperature conditions (“present day” less toxic cells). In addition to comparing uptake and depuration of domoic acid from ingested cells grown under these contrasting conditions, we will also be comparing the effects of warming and acidification on the grazers themselves by carrying out the feeding experiments under high CO2/temperature or present day CO2/temperature conditions. These experiments will answer the dual questions: 1) How does elevated toxin content in diatom prey due to growth at high CO2 and temperature affect trophic transfer of domoic acid?, and 2) How is trophic transfer of domoic acid affected by potential alterations in grazer feeding physiology and behavior under high CO2 and temperature conditions?

Rationale:
Accurately predicting the impacts of toxic Pseudo-nitzschia blooms in a rapidly acidifying and warming ocean is a top priority for marine resource managers, policy makers, and the fishing and aquaculture industries. Our efforts to obtain crucial information about the potential for increases in future toxic events that could lead to harvesting closures are strongly endorsed by seafood industry representatives, represented by the California Wetfish Producers Association. Our project aims to predict how ocean acidification and warming will affect toxin transfer to planktonic and benthic grazers, since they are the first key step in the trophic bio-concentration pathway that determines how much domoic acid ultimately ends up in valuable harvested resources including shellfish, squid, and fish.

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