Comparative analysis of the 1980s and 2004 macrozooplankton composition and distribution in the vicinity of Kerguelen and Heard Islands: seasonal cycles and oceanographic forcing of long-term change
In this paper we present historic macrozooplankton data from the vicinity of the Kerguelen Islands during the Ukrainian Skif and Kalper (SKALP) surveys in February, April and July-August of 1987 and February 1988, in addition to a monthly composite of seston data collected during ad hoc cruises between 1980 and 1990. We compare these data with more recent surveys conducted at Heard Island (February 2004) and the Prince Edward Islands (PEI) to the west of the Kerguelen Plateau (April 1997 and April 2003). A strong seasonal cycle of seston and macrozooplankton biomass was evident in the SKALP surveys, peaking between December and April. Kerguelen Plateau and PEI macrozooplankton were generally dominated by euphausiids, chaetognaths and amphipods, but salps were of major significance to the south of the PEI. Comparison of species composition at the Kerguelen Islands in 1987/1988 with Heard Island in 2004 lends biological support to recent estimates from satellite altimetry that the Polar Front has shifted from passing north of the Kerguelen Islands to passing south of Heard Island in 2003. As key food-web components, long-term changes and regional differences in macrozooplankton communities have significant implications for food web dynamics with respect to the type, quality and quantity of macrozooplankton prey available to top predators.