Euphausiid spatial displacements and habitat shifts in the southern California Current System in response to El Nino variability

We analyzed spatial distributions of 10 euphausiid species in the southern California Current System across seven El Nin?o events (1951?2018) and the 2014?15 Warm Anomaly to determine variations in habitat utilization and reproduction during Eastern Pacific (EP) and Central Pacific (CP) Nin?os. Our goal was to characterize the main forcing mechanisms by which El Nin?o events influence these dominant species. Our findings suggest cool-water euphausiids respond predominantly to changing in situ habitat conditions during El Nin?o, while subtropical species require initial advection to increase in the southern CCS. Cool-water coastally-associated species (Euphausia pacifica, Thysanoessa spinifera) compress shoreward and retract poleward to upwelling waters during EP Nin?os, likely in response to offshore warming. A subtropical coastal species (Nyctiphanes simplex) extends poleward nearshore during EP Nin?os, suggesting anomalous advection, but increases only moderately and variably off southern California during CP Nin?os. A Tropical Pacific-Baja California species (Euphausia eximia) only appears off southern California in spring during El Nin?o years (EP, some CP), suggesting direct advection and low tolerance for cooler, fresher conditions. Subtropical offshore species (Euphausia gibboides, Euphausia recurva, Stylocheiron affine, Euphausia hemigibba) expand shoreward during most Nin?os (strongest during 2014?15 Warm Anomaly) and show moderate in situ post-event persistence, suggesting combined influence of advection and temporarily favorable habitat nearshore. Regionwide temperate species (Nematoscelis difficilis, Thysanoessa gregaria) contract only moderately shoreward during some Nin?os. Predictions of Year 2100 distributions using generalized additive models suggest future non-Nin?o conditions and CP Nin?os will produce regionwide in situ increases in subtropical species and moderate poleward and onshore expansions, while EP Nin?os will produce continued nearshore habitat compression and reduced abundance of coastal species. Understanding zooplankton spatial responses to El Nin?o can help predict community compositional shifts under other ocean changes (e.g., long-term trends, basin-wide warm anomalies).

Automated summary

The study found that cool-water euphausiid species are more susceptible to changes in habitat conditions during El Niño events, while subtropical species are more dependent on initial advection. Cool-water species compress shoreward and retract poleward during EP Niños, while subtropical species expand northward nearshore during EP Niños.