Interannual variability in surface mesozooplankton in the Western Antarctic Peninsula during two anomalous years

Abstract

Zooplankton play a key role in the Southern Ocean, are closely linked to oceanographic variations and are highly sensitive to environmental changes. The Western Antarctic Peninsula (WAP) is a critical global climate hotspot where the variability and vulnerability of marine ecosystems are particularly evident. This study aims to characterize the variability of surface mesozooplankton across the Gerlache (GS) and Bransfield (BS) straits. Data were collected with a continuous plankton recorder (CPR) during the austral summer of 2016 (CPR-34 route) and 2017 (CPP-35 route), enabling extensive spatial mapping of zooplankton communities. In 2016, the average sea surface temperature (SST) was 0.57 °C, whereas in 2017, it increased to a maximum of 2.13 °C. The surface salinity (SS) was lower in 2017 (average 33.86). High chlorophyll-a values were recorded in the GS in 2016 (43.78 mg m⁻³). PERMANOVA revealed significant differences in community composition between the year and location site. Beta diversity analysis revealed nestedness in 2016, with Copepoda dominating the mesozooplankton community, particularly Metridia gerlachei and Metridia longa, which accounted for 85% of the total abundance of Copepoda. In 2017, events of replacement, known as turnover, were observed, with a shift from copepods to salps along with lower local diversity. The BS had a relatively high abundance in both years, reflecting the sampling periods and dial migration patterns. CCA revealed positive correlations between salps and temperature and negative correlations between salinity and copepods. These findings highlight distinct community structure patterns driven by specific environmental conditions linked to major climatic events, i.e., the ENSO and SAM, offering insights into zooplankton responses to anomalous oceanographic conditions in the WAP.