CCEIII: Persistent functional relationships between copepod egg production rates and food concentration through anomalously warm conditions in the California Current Ecosystem

Abstract

We hypothesized that copepod egg production rates would be suppressed relative to their normal functional relationships with food availability during the NE Pacific warm anomalies of 2014–2015 and the El Niño event of 2015–2016. We also hypothesized that copepods would show increased rates of egg production and recruitment in association with ocean fronts. Three species of copepods (Calanus pacificus, Metridia pacifica, and Eucalanus californicus) were incubated at sea in simulated in situ conditions to ascertain egg production rates and egg hatching success during a sequence of 3–5 California Current Ecosystem-Long Term Ecological Research (CCE-LTER) cruises across diverse ocean conditions. Several indices of food availability were measured. The warm events had no significant effect on egg production rates measured in the experiments conducted here. Egg production and net naupliar production rates varied markedly among copepod species and across spatial gradients, but relationships with food concentration during warm events did not consistently diverge from functional relationships during El Niño-neutral conditions. Egg production was most commonly elevated inshore compared to offshore, but was not elevated within fronts. The egg production of C. pacificus was best explained by total Chl-a, while E. californicus was best explained by the > 20 size fraction of Chl-a. M. pacifica showed no relationship between egg production and any food metric tested. C. pacificus showed higher EPR than the other two species in virtually all conditions encountered, which may contribute to its numerical dominance throughout the region.