Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 8859
Title: Initiation and development of a toxic and persistent Pseudo-nitzschia bloom off the Oregon coast in spring/summer 2015
Author: Xiuning Du, William T. Peterson, Jennifer L. Fisher, Matt Hunter, Jay O. Peterson
Publication Year: 2016
Journal: PLoS ONE
Volume: 11
Issue: 10
Pages: e0163977
Keywords: Pseudo-nitzschia,harmful algal blooms,razor clam,nutrient limitation,the Blob,

In spring/summer 2015, a toxic bloom by the diatom Pseudo-nitzschia (PN) occurred along the west coast of the United States which led to closures of the harvest of razor clams and Dungeness crabs.  Twice monthly observations of temperature, salinity, nutrients, chlorophyll and phytoplankton species composition allowed us to track oceanographic conditions preceding and during the development of the bloom.  PN cells were first detected during late winter 2015.  A PN bloom was initiated following the onset of coastal upwelling in mid-April; subsequent peaks in May and June were sustained by episodic upwelling events and reached magnitudes of 105 cells/L and 106 cells/L, 90% and 40% of the total diatom abundance, respectively.  The bloom temporarily crashed in July due to a lack of upwelling, but PN cells increased again in August due to a resumption of upwelling albeit with lower magnitude.  Macronutrient conditions prior to this bloom likely played a critical role in triggering the bloom and its toxicity (particularly silicic acid limitation stress).  Nutrient stress preceding the toxic bloom was related to two oceanographic events:  an anomalously warm and thick water mass that occupied the northern North Pacific from September 2014 through 2015 leading to a highly stratified water column, and the drawdown of nitrate and silicic acid during an unusually intense winter phytoplankton bloom in February and early March 2015.

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Theme: Ecosystem approach to improve management of marine resources
Foci: Describe the interaction between human activities, particularly harvest of marine resources, and ecosystem function.
Assess ecosystem status and trends.