A comparative analysis of coastal and shelf‐slope copepod communities in the northern California Current system: Synchronized response to large‐scale forcing?

Abstract

The synchrony between coastal and shelf‐slope copepod communities was investigated in the northern California Current (NCC) system, a strong upwelling zone, using time series of zooplankton sampled from a nearshore station (9 km offshore, water depth 62 m) and a shelf‐slope station (46 km offshore, water depth 297 m). Long‐term trends and seasonal changes were constructed for the dissimilarity index (Euclidean distance) between the two stations and for the biomass of three different copepod assemblages at the two stations: cold neritic, southern, and warm neritic copepods. The dissimilarity between the community structures of the two stations showed little variation in the long‐term trend, but exhibited a clear seasonal pattern. All three copepod assemblages showed similar long‐term trends in relation to the large‐scale forcing as indexed by the Pacific Decadal Oscillation at both stations, but variations in the long‐term trend at the nearshore station were much higher than the offshore station. Most copepod groups exhibited regular seasonal patterns at both stations except southern copepods at the nearshore station. All three copepod assemblages exhibited more pronounced seasonal fluctuations at the nearshore station compared with the slope station, and this difference is likely driven by higher productivity nearshore fueled by nutrient‐enriched upwelled water. Copepods in the inshore and offshore waters in the NCC ecosystem showed synchronized response to the large‐scale variability in physical forcing and copepods in the coastal waters were more responsive to local perturbations than were those in the slope waters.