New research sponsored by NCCOS explains what might have caused the high toxicity in Monterey Bay, CA during the massive 2015 toxic bloom of the marine diatom Pseudo-nitzschia along the West Coast of the United States. Based on NCCOS research, warm water, nutrients, or a combination of factors may have caused the bloom and to some extent the toxicity.

In the late spring-summer of 2015 a massive toxic bloom of the marine diatom Pseudo-nitzschia (PN), stretching from central California to the Alaska Peninsula, resulted in significant impacts to coastal resources and marine life. NOAA worked closely with federal, state, tribal, academic, and other partners to respond to this unprecedented harmful algal bloom (HAB). NOAA's National Centers for Coastal Ocean Science (NCCOS) contributed internal and sponsored research to understand the causes of the bloom, and NCCOS Event Response funding provided support for sampling and toxin analysis.

Building on a suite of NCCOS-funded research studies such as the California HAB 'hotspots ' project, NCCOS ECOHAB Program researchers (MBARI, UCSC, Moss Landing Marine Laboratories, NOAA NCCOS) published the results of the collaboration in Geophysical Research Letters . The study shows that toxicity of the 2015 large PN bloom in Monterey Bay was enabled by the relative availability of nitrate and silicate, nutrients required by diatoms. Some PN produce the neurotoxin, domoic acid (DA), containing nitrogen. When only nitrate is available, the diatoms cannot grow but they can still become toxic - more so over time. DA was measured using two Environmental Sample Processors (ESP), a toxin sensor developed by NCCOS, moored at the southern and northern ends of Monterey Bay and water samples collected by an Autonomous Underwater Vehicle (AUV) to detect high biomass phytoplankton patches.

Other studies in other regions associated the bloom with anomalously high surface temperatures, but Monterey Bay had normal temperatures at the time of the bloom. That said, the other studies did not specifically examine nitrate:silicate ratios and their relationship to PN bloom toxicity.

In order to predict toxicity timing of shellfish and other fishery resources, the critical unanswered question is which environmental factors determine toxicity. This study addresses that question for one species of PN that may lead researchers studying these blooms in other areas to investigate whether nitrate:silicate ratios control toxicity there as well.

For more information, contact Quay.Dortch@noaa.gov or Greg.Doucette@noaa.gov.

Citation:Ryan, J.P., R.M. Kudela, J.M. Birch, M. Blum, H.A. Bowers, F.P. Chavez, G.J. Doucette, K. Hayashi, R. Marin III, C.M. Mikulski, J.T. Pennington, C.A. Scholin, G.J. Smith, A. Woods, and Y. Zhang (2017). Causality of an extreme harmful algal bloom in Monterey Bay, California during the 2014–2016 northeast Pacific warm anomaly.Geophysical Research Letters:44, 05 June 2017. DOI:10.1002/2017GL072637