Impacts of Marine Heatwaves on Euphausia pacifica in the Northern California Current

“The Blob” was a persistent warm water mass which occurred in the northeastern Pacific Ocean from fall 2013 to winter 2015/16. It started offshore, and reached the northern California and Oregon coast in September 2014. Temperatures within the Blob were 2-4 degrees Celsius above average and anomalously warm conditions extended up to 100 m depth. We tracked the lipid content of adult Euphausia pacifica prior to, during, and after effects of the Blob were felt locally to determine its potential impact on local food webs. E. pacifica have been collected from the upper 100 m along the Trinidad Head Line (northern California, USA) since May 2013. During the period when the temperature signal of the Blob was present along the coast (fall 2014 to summer 2015), lipid content (% of dry mass) of E. pacifica was significantly lower (33-66%) than during the same time period a year prior. These results suggest that the quality of food available to E. pacifica predators (including fish, marine mammals, and birds) was significantly lower when positive temperature anomalies were strongest along the coast. However, impacts of the Blob on E. pacifica appeared to be short-lived in our data set, and during fall 2015 to winter 2016/17, lipid content was similar to or approaching pre-Blob levels. A new marine heatwave has recently developed in the northeastern Pacific Ocean. Regular sampling allows us the opportunity to assess the impacts of the 2019 heatwave on E. pacifica. We will extend our previous data set with observations from summer 2019-winter 2019/2020 to understand whether our finding of reduced E. pacifica body lipids during the Blob is a typical response to marine heatwaves in the northeastern Pacific.