Macrozooplankton community structure and trophic interactions differ across a sub‐Antarctic shelf break, independent of Antarctic krill

The South Georgia continental shelf break is a highly productive and biodiverse region of the Southern Ocean, with abundant macrozooplankton forming the foundation of off- and on-shelf communities. Antarctic krill (Euphausia superba) are a major component of these communities and can dominate total biomass. In this study, we analyze a new 10-year timeseries of spatially varied net samples from summer campaigns spanning the South Georgia shelf region to examine patterns of variability in macrozooplankton species abundance on- and off-shelf in the austral summer. We found total net catch abundance was similar on- and off-shelf, with particularly high abundances when Antarctic krill were present. Overall trends showed on-shelf to be more variable in community composition, and more likely to contain high abundances of Antarctic krill. Community composition in the off-shelf environment remained consistent between sites and with time and was more species rich than the on-shelf community. Our analysis further revealed strong statistical associations in co-occurrence between certain taxa, which sometimes varied between on-shelf and off-shelf communities. In a number of instances, these associations reflect either feeding guilds (taxa with similar prey preferences) or predator–prey co-occurrence. Overall, although community composition differed between on-shelf and off-shelf environments, these compositions appeared to be relatively stable in space and time irrespective of the presence or absence of Antarctic krill. This finding, that the macrozooplankton communities appear relatively resilient to intra-decadal environmental fluctuations in abundance, has particular importance when considering the impact of rapid regional climate change and potential longer-term changes in the biomass of Antarctic krill on the wider South Georgia pelagic ecosystem.