Latitudinal transitions of eddy-affected zooplankton abundance in the mid-latitude North Atlantic

Mesoscale eddies play a critical role in marine ecosystems by regulating ocean environments and thereby influencing marine life. By integrating zooplankton observations from the Continuous Plankton Recorder (CPR) project with satellite-derived sea surface temperature (SST), chlorophyll (Chl) concentration, and eddy datasets based on sea surface height, we investigate the impacts of eddy populations on zooplankton community abundance in the North Atlantic. To comprehensively assess both the abundance and richness of zooplankton communities, we introduced the Abundance Index as a unifying metric. The mid-latitude North Atlantic is segmented into three latitudinal zones: the southern zone (35°N–45°N), the middle zone (45°N–55°N), and the northern zone (55°N–70°N). Our analysis revealed distinct annual variations in the Abundance Index across the three zones from 1993 to 2017. The Abundance Index was consistently higher within cyclonic eddy (CE) cores compared with anticyclonic eddy (AE) cores in the southern and northern zones, contrasting with the patterns in the middle zone. However, the composite patterns of eddy-affected Chl and SST were similar across all zones. By employing six machine learning models, we assessed the feature importance (FI) of log-transformed Chl (log-Chl) and SST in explaining the Abundance Index. Log-Chl was found to have a greater impact than SST, particularly in the northern zone, highlighting the greater importance of food availability relative to ambient temperature. Significant shifts in the Abundance Index differences between AE and CE cores were detected in 1998, 2002, and 2003 in the southern, middle, and northern zones, respectively, suggesting that optimal habitats may have shifted in response to ocean climate change. These findings provide deeper insights into the effects of mesoscale eddies on zooplankton communities and highlight their broader implications for marine ecosystem dynamics.