Abstract
The California Current System (CCS) has experienced large fluctuations in environmental conditions in recent years that have dramatically affected the biological community. Here we synthesize remotely sensed, hydrographic, and biological survey data from throughout the CCS in 2019–2020 to evaluate how recent changes in environmental conditions have affected community dynamics at multiple trophic levels. A marine heatwave formed in the north Pacific in 2019 and reached the second greatest area ever recorded by the end of summer 2020. However, high atmospheric pressure in early 2020 drove relatively strong Ekman-driven coastal upwelling in the northern portion of the CCS and warm temperature anomalies remained far offshore. Upwelling and cooler temperatures in the northern CCS created relatively productive conditions in which the biomass of lipid-rich copepod species increased, adult krill size increased, and several seabird species experienced positive reproductive success. Despite these conditions, the composition of the fish community in the northern CCS remained a mixture of both warm- and cool-water-associated species. In the southern CCS, ocean temperatures remained above average for the seventh consecutive year. Abundances of juvenile fish species associated with productive conditions were relatively low, and the ichthyoplankton community was dominated by a mixture of oceanic warm-water and cosmopolitan species. Seabird species associated with warm water also occurred at greater densities than cool-water species in the southern CCS. The population of northern anchovy, which has been resurgent since 2017, continued to provide an important forage base for piscivorous fishes, offshore colonies of seabirds, and marine mammals throughout the CCS. Coastal upwelling in the north, and a longer-term trend in warming in the south, appeared to be controlling the community to a much greater extent than the marine heatwave itself.
Highlights
The California Current System (CCS) off the west coast of North America is a highly dynamic and productive marine ecosystem that supports a great diversity of birds, finfishes, invertebrates, and marine mammals
The 2020 marine heat wave” (MHW) differed from previous MHW events in that it coincided with an exceptionally strong North Pacific High during January to March 2020 (Figures 1, 14)
The strong late-winter North Pacific High in 2020 resulted in early seasonal upwelling and cooler sea surface temperatures along the shelf in the northern CCS (Figures 4, 6), which contributed to the MHW remaining offshore (Figure 3)
Summary
The California Current System (CCS) off the west coast of North America is a highly dynamic and productive marine ecosystem that supports a great diversity of birds, finfishes, invertebrates, and marine mammals. There is great interannual variability in environmental conditions in the CCS driven largely by basin-scale climate variability (Di Lorenzo et al, 2013). Basin-scale forcing affects winds, alongshore transport, and coastal wave propagation in the CCS (Jacox et al, 2015), thereby controlling seasonal and regional coastal upwelling (Checkley and Barth, 2009). The CCS experiences high seasonal wind-driven upwelling in the spring and summer, which creates stronger equatorward currents of cooler, nutrient-rich water, and relatively high primary productivity in much of the system (Huyer, 1983; Bograd et al, 2009; Jacox et al, 2018b). The strength and timing of upwelling vary considerably, and this variability affects the production and distribution of species at all trophic levels via bottom-up interactions. The zooplankton community is a key intermediary in these interactions
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