Initiation and Development of a Toxic and Persistent Pseudo-nitzschia Bloom off the Oregon Coast in Spring/Summer 2015

Abstract

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, 40% and 90% 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.

Climatic regulation of the neurotoxin domoic acid

“…S2), and DA reached record highs in CA mussels and lobster (19); high DA was detected in coastal waters from at least central CA north to central OR (26). In 2015, extensive NE Pacific warming coincided with an unprecedented, record-setting DA event from CA to WA (20,38).…”

Phytoplankton Community Structure in 2011–2013 Compared to the Extratropical Warming Event of 2014–2015

“…However, local wind‐induced upwelling events have more direct effects on short‐term nutrient availability to phytoplankton growth and also to the selection of dominants (Du et al, ). The increased proportion of dinoflagellates and the toxic Pseudo‐nitzschia bloom in the warm mass group were likely related to the suppressed nitrate and silicate concentrations (Du et al, ). Similar findings of climatic regulation on increases of dinoflagellate percentage and Pseudo‐nitzschia were reported in the Iberian coastal upwelling system associated with rising sea temperature and the North Atlantic Oscillation (Perez et al, ).…”

“…Warm ocean events, such as strong El Niño and periods of positive Pacific Decadal Oscillation (PDO), have known negative impacts on the ecosystem of the California Current: reduced production of the upper trophic predators (Barber & Chavez, 1983;Peterson et al, 2014;Sydeman et al, 2006), increased frequency of harmful algal blooms (Du et al, 2011(Du et al, , 2016McCabe et al, 2016;McKibben et al, 2015McKibben et al, , 2017, and shifts in copepod community from lipid-rich to lipid-poor species (Fisher et al, 2015;Hooff & Peterson, 2006;Peterson & Keister, 2003). Warm ocean conditions suppress primary production (Thomas et al, 2009) and bring changes in phytoplankton community composition (Balech, 1959;Bolin & Abbott, 1963;Du et al, 2015;Venrick, 2012).…”

Ocean acidification stress index for shellfish (OASIS): Linking Pacific oyster larval survival and exposure to variable carbonate chemistry regimes

“…Cohort 4 responded differently in pre-settlement survival with respect to buffering than the other three cohorts, resulting in highest survival in the continuously unbuffered treatment (Figure 4D). In 2015, an unprecedented harmful algal bloom (HAB) of diatoms, Pseudonitzschia spp., producers of neurotoxin domoic acid (DA), was detected along the West Coast of the US (Cavole et al, 2016;Du et al, 2016;McCabe et al, 2016;McKibben et al, 2017). One particularly severe peak coincided with the culture of Cohort 4 in early June 2015 (Du et al, 2016;Figure 4 in McCabe et al, 2016), coinciding with low embryo survival and arrested growth of later larval stages at WCH.…”