A warm anomaly in the upper ocean, colloquially named “the Blob,” appeared in the Gulf of Alaska during the calm winter of 2013–2014, spread across the northern North Pacific (NP) Ocean, and shifted eastward and onto the Oregon shelf. At least 14 species of copepods occurred which had never been observed in shelf/slope waters off Oregon, some of which are known to have NP Gyre affinities, indicating that the source waters of the coastal “Blob” were likely of both offshore (from the west) and subtropical/tropical origin. The anomalously warm conditions were reduced during strong upwelling in spring 2015 but returned when upwelling weakened in July 2015 and transitioned to downwelling in fall 2015. The extended period of warm conditions resulted in prolonged effects on the ecosystem off central Oregon, lasting at least through 2016. Impacts to the lower trophic levels were unprecedented and include a novel plankton community composition resulting from increased copepod, diatom, and dinoflagellate species richness and increased abundance of dinoflagellates. Additionally, the multiyear warm anomalies were associated with reduced biomass of copepods and euphausiids, high abundance of larvaceans and doliolids (indictors of oligotrophic ocean conditions), and a toxic diatom bloom (Pseudo‐nitzschia) throughout the California Current in 2015, thereby changing the composition of the food web that is relied upon by many commercially and ecologically important species.

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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.

Phytoplankton species were enumerated from 72 samples collected biweekly during the upwelling season (May to August) of 2001−2010 to test for effects of interannual variations in upwelling and decadal basin-scale variability on phytoplankton species composition and community structure. Cluster analysis of phytoplankton community structure identified 7 groups; 1 group was dominated by dinoflagellates while the other groups were dominated by diatoms but with variable ratios of diatom-to-dinoflagellate abundance ranging from 4 to 847. The most abundant diatoms were Thalassiosira spp., Chaetoceros spp., Asterionellopsis glacialis, Cylindrotheca closterium, Leptocylindrus spp., Nitzschia and Pseudo-nitzschia spp., with dominance varying among the 7 groups. Variations in phytoplankton community structure were not related to the strength of upwelling within a given year; rather, differences were related to when a sample was collected within an upwelling/downwelling cycle. Community structure was also analyzed by non-metric multidimensional scaling ordination. The x-axis scores of the ordination, which is an index of community structure, were correlated with the Pacific Decadal Oscillation (PDO) but not with seasonally averaged coastal upwelling strength. Positive values of the index corresponded with positive PDO years (2002−2007), and negative index values with negative PDO years (2001, 2008−2010). Thus changes in the sign of the PDO seem to be more influential in explaining the interannual variations in phytoplankton community structure than seasonally averaged coastal upwelling.

Coastal waters of the Northern California Current experienced “normal” ocean conditions in 2011–2012, weak upwelling in 2013–2014, then suddenly warmed in September 2014. The response of phytoplankton community structure to contrasting ocean conditions was determined from samples collected off Newport, Oregon. Cluster analysis identified three prominent phytoplankton community types: one that occurred during the upwelling season characterized by the highest abundance and diversity of diatoms, a preupwelling/relaxation community characterized by lower abundance, lowest diversity of diatoms and dinoflagellates, and another one associated with the warm anomalies from September 2014 through 2015 with reduced diatom abundance and diversity but the highest dinoflagellate diversity. The changes of diatom and dinoflagellate community were correlated with local factors (silicate, silicate: nitrate ratios, temperature, and salinity), and with the Pacific Decadal Oscillation.

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