Temporal patterns in the distribution, biomass and community structure of macrozooplankton and micronekton within Port Foster, Deception Island, Antarctica

The pelagic community within the flooded caldera of Deception Island, Antarctica, was sampled with a 10-m2 opening-closing MOCNESS trawl on five cruises between March 1999 and November 2000. Collections were made in 50 m strata from the surface to 150 m depth in an area with a bottom depth of 155–160 m. From March 1999 through February 2000 the pelagic community was dominated by krill, primarily Euphausia crystallorophias and E. superba, which made up >94% of total pelagic biomass on a dry-weight basis. Community composition shifted during early 2000, and samples from May and November 2000 contained a more diverse assemblage and large numbers of cydippid ctenophores, comprising ca. 30–35% of pelagic biomass on a dry weight basis. E. crystallorophias, which made up nearly 85% of the pelagic biomass in November 1999, declined to 5.8% during November 2000. The change in composition was accompanied by displacement of the biomass mode to greater depths, due to the deeper occurrence and lack of diel vertical migration in ctenophores, compared to krill. Integrated water-column biomass increased substantially from 1999 to 2000, primarily because of elevated abundances of gelatinous zooplankton and the presence of significantly larger krill during 2000.