Presenter: WESLEY STRASBURGER (Alaska Fisheries Science Center)

Description:
The eastern North Pacific experienced a prolonged heat wave during the end of the last decade, manifested by high near-surface sea temperature anomalies in the south-central Gulf of Alaska (GOA). The event provided a natural experiment on the response of southern GOA ecosystem to a dramatic change in sea temperature. Spatial and temporal variability in zooplankton communities following the culmination of the heat wave was investigated as a part of the NOAA Eastern GOA Ecosystem Assessment program in 2016-2017. Here, we discuss potential impacts of dense doliolid (Dolioletta tritonis) swarms observed during both years on pelagic food web. Doliolids are filter feeders capable of ingesting a wide variety of prey. Their high individual feeding rates in combination with explosive reproductive and growth potential appear to substantially reduce local resources resulting in sharp decrease in abundance of other zooplankton grazers (e.g., Calanus pacificus and Eucalanus bungii). On the other hand, doliolids on average comprised 40% to 90% of juvenile sablefish (Anaplopoma fimbria) diet by weight, indicating an important shift in the energy pathways toward upper trophic levels. Thus, we speculate that doliolid blooms in the GOA, if they become persistent, will profoundly change the GOA marine food web structure with potential repercussions to the ocean-based economy.