Award: OCE-1614359

Intellectual Merit Our major goals were to quantify the effects of El Niño on key rate processes that control the structure of the pelagic food web and rates of elemental cycling. The processes measured included primary and secondary production, grazing, dissolved iron effects on phytoplankton growth, carbon and nitrogen recycling, and elemental export in both particulate and dissolved forms. These measurements were compared to comparable measurements by the CCE-LTER group in this region during El Niño-neutral conditions. As El Niño 2015-16 followed major Pacific Warm Anomalies of 2014-15, the effects of both climate perturbations were analyzed. Our results illustrate pronounced elevations in sea surface temperature, depressions in phytoplankton chlorophyll-a, altered zooplankton community composition, and decreased incidence of surface ocean fronts in our study site during both the Warm Anomalies and El Niño. Some of the processes underlying these changes include decreased availability of nutrients, changes in the rate of photosynthesis in relation to irradiance, and depressed mesozooplankton grazing rates. However, the egg production rate of three species of planktonic copepods, a proxy for secondary production by zooplankton, was not significantly depressed during El Niño. Similarly, bacterial secondary production was not significantly altered during our El Niño cruise, but was depressed in the preceding Warm Anomaly conditions, probably due to limitation by available carbon substrates. Total zooplankton carbon biomass was relatively unaffected by El Niño, but this masks highly significant changes in community composition, especially of the species composition of euphausiids (krill). Phytoplankton community changes were modest, and confined to slightly increased abundances of chlorophytes, prasinophytes, and Synechococcus. Iron limitation was not a major factor structuring the phytoplankton community in nearshore regions during the cruise, although a small but significant reponse to iron addition in deckboard incubations was detected in transitional waters somewhat further offshore. Biogenic silica fluxes mediated by large single-celled protists (phaeodarians) were highest in the offshore region, where diatoms formed a minor part of the flux. Overall, although we detected major responses of the pelagic ecosystem to El Niño, we found that most functional relationships between controlling variables were altered relatively little. For example, the relationships between carbon export and primary production, biogenic silica export and primary production, phytoplankton growth rate and iron:nitrate ratios, zooplankton grazing and phytoplankton concentration, copepod egg production and food concentration showed little change during El Niño. These results suggest that the CCE-LTER space-for-time substitution – i.e., using spatial variability as a proxy for how the ecosystem will change over time – is a viable approach, even during El Niño perturbations. This finding makes it feasible to build ocean ecosystem models forecasting the effects of future El Niños. Broader Impacts CCE-LTER led a national workshop on Forecasting ENSO Impacts on Marine Ecosystems of the US West Coast at Scripps. A series of articles resulting from this workshop was published in the CLIVAR/OCB Newsletter "Variations" in Feb. 2017. The workshop led to a US CLIVAR Webinar on "Forecasting ENSO Impacts in the California Current System." The workshop also stimulated a plan to develop a Research Coordination Network devoted to Marine Ecosystem Forecasts (MECOFOR), including highlighting the effects of El Niño. Art Miller was active in numerous outreach events associated with discussing climate change impacts with the general public. REU students participated in summer research internships. Our Education, Outreach, and Capacity Building (EOCB) team created several activities. These included Full Moon pier walks, background information and activities taken to six local middle schools, and a Teacher Professional Development Workshop where educators received training in science content and hands-on lessons designed to increase their understanding of El Niño and its impacts on the California Current Ecosystem. The CCE site was featured at Birch Aquarium?s SEA (Science! Exploration! Adventure!) Days event. Six members of CCE participated in the Exploring Ocean STEM Careers Night at BAS. An Explore-It Plankton station is now open daily to guest at BAS. A new CCE investigator, Alexis Pasulka, initiated a coastal pier time series at California Polytechnic University, measuring temperature and chlorophyll, together with samples taken to characterize the nearshore phytoplankton community using molecular genetics. Plankton photographs from the Stukel lab taken on the CCE El Niño cruise have been widely disseminated and used as outreach tools in multiple settings. A dance video was created depicting an imaginative day in the life of a marine biogeochemistry graduate student. We developed a quantitative basis for formulating ecosystem models, to improve understanding and forecasting of future El Ninos and possibly ocean warming. We have begun a collaboration with scientists at NCAR (the National Center for Atmospheric Research) to develop a numerical model of a composite El Niño-ecosystem response in the California Current System. El Niño-related changes in key plankton species in the pelagic food web are likely to influence feeding and breeding success of a variety of fishes, marine mammals, and seabirds. Last Modified: 04/02/2018 Submitted by: Mark D Ohman