Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 8261
Title: Monitoring Oregon Coastal Harmful Algae: Observations and implications of a harmful algal bloom-monitoring project
Author: S. Morgaine McKibben, Katie S. Watkins-Brandt, A. Michelle Wood, Matthew Hunter, Zach Hunter, Alyssa Hopkins, Xiuning Du, B.-T. Le Eberhart, W. T. Peterson, Angelicque E. White
Publication Year: 2015
Journal: Harmful Algae
Volume: 50
Pages: 32-44
DOI: 10.1016/j.hal.2015.10.004
Keywords: Oregon coast, harmful algal bloom, domoic acid, saxitoxin, Alexandrium, Pseudo-nitzschia,harmful algal bloom

The planktonic biodiversity and metabolism of the upper ocean is modulated by local to basin-scale physical and chemical processes that occur over daily and weekly to inter-decadal timescales; these collective processes regulate phytoplankton community structure and bloom initiation, including harmful algal blooms (HABs). Here we summarize 5 years of Oregon coast HAB monitoring (2007-2012) and discuss the most significant HAB events during this period relative to potential causal factors. A 2009-2010 basin-scale warming event was associated with changes in local conditions and notable HAB events: coastwide shellfish harvesting closures due to saxitoxins (STX) in the fall of 2009 and closure of central Oregon coast shellfish harvesting due to elevated levels of domoic acid (DA) in the summer of 2010. The warming event began in the latter part of the 2009 upwelling season, enhancing late-summer conditions that often select for dinoflagellate growth. The warming persisted through June 2010, delaying the seasonal transition to upwelling-favorable conditions. We hypothesize that a delay in nutrient supply stressed the phytoplankton community, inducing DA production by Pseudo-nitzschia spp. In regards to HAB monitoring in upwelling regimes, we suggest that (1) water column concentrations of pDA > 103 ng L-1 can be used as a threshold for early-warning of shellfish DA toxicity and (2) approximately bi-weekly, or shorter, monitoring of Alexandrium in the surf zone and/or offshore can provide advance notice of STX contamination of shellfish. Both metrics are particularly useful if coupled with monitoring for onshore flow, which occurs during downwelling/relaxation events and facilitates interaction between offshore waters and shellfish.