Time-series analysis of hydrological and biological variability on the Prince Edward Island (Southern Ocean) shelf

Eulerian time-series were completed at three sites on the south eastern shelf of the Sub-Antarctic Prince Edward Islands (PEI), from 9 to 27 April 2000, to investigate the spatial and temporal variability of mesozooplankton communities in relation to on-shelf hydrodynamics. Surface temperature and phytoplankton biomass were recorded daily at all three sites, while two Bongo net tows and vertical temperature profiles were collected daily at two sites. Contrary to predictions of on-shelf water retention at low ambient current velocities, cross-correlation analysis identified a northward advection of ∼8.23 cm s−1 over the study area. Day to day changes in both physical and biological parameters were associated with cross-shelf advection. However, sea temperature had a narrow range of 6.2–7.4°C, while average between sample Bray–Curtis similarity in zooplankton communities was high, exceeding 75%. The relatively consistent average sample biomass amounted to ∼494 tonnes dry weight of mesozooplankton per day being advected onto the south eastern sector of the PEI shelf. We hypothesise that the observed stability of both physical and biological parameters was due to the Sub-Antarctic Front, with its high volume transport and steep physical gradients, being far to the north of the islands. Spatial and temporal variability of hydrodynamics on the PEI shelf, and particularly its relationship to shifting frontal positions, is highlighted as a future research area necessary to quantify the gross delivery of allochthonous biomass to the PEI ecosystem.