Polar Biol (1996) 16: 271—286  Springer-Verlag 1996 ORIGINAL PAPER E.A. Pakhomov · C.D. McQuaid Distribution of surface zooplankton and seabirds across the Southern Ocean Received: 28 November 1994/Accepted: 11 August 1995 Abstract Surface zooplankton and seabird densities and community composition in the Atlantic (between Cape Town and Sanae) and Pacific (between New Zealand and the Ross Sea) sectors of the Southern Ocean are described and related to oceanographic fea- tures. Samples were collected during two return voy- ages aboard the MV Benjamin Bowring as part of the Transglobe Expedition (1979—1981). High abundances of surface zooplankton and seabirds were consistently observed within the main frontal systems of the Southern Ocean. Generally, on a mesoscale significant correlations between surface temperature and the distribution of zooplankton or seabirds were observed. On a macroscale, the geographical positions of the zooplankton and seabird communities coincided with specific water masses. The results of this study suggest that appropriate food availability rather than water temperature is important for the determination of sea- bird distribution. The ecological importance of the recently described frontal zone associated with the northern boundary of the maximum winter expansion of sea ice is confirmed by biological data obtained in this study. Introduction The Southern Ocean is not ecologically uniform and is subdivided into several distinct circumpolar zones by strong frontal systems (Deacon 1982; Hempel 1985). Differences in plankton and seabird communities are expected in each of the zones (e.g. Rustad 1930; Deacon 1982; Shuntov et al. 1981; Croxall 1984). While inter- frontal areas have a relatively uniform plankton bio- E.A. Pakhomov ( ) · C.D. McQuaid Southern Ocean Group, Department of Zoology and Entomology, Rhodes University, P.O. Box 94, Grahamstown, 6140, South Africa mass and seabird abundance, the frontal systems them- selves are characterised by increased biological produc- tivity and biomass at all trophic levels of the pelagic ecosystem (e.g. Griffiths et al. 1982; Lutjeharms et al. 1985; Pakhomov et al. 1994). A recent model of the Antarctic ecosystem suggests that air-breathing sea- birds and mammals, which consume macrozooplan- kton and micronekton, may transfer, via respiration, as much as 20—25% of photosynthetically fixed carbon into the atmosphere (Huntley et al. 1991). It has also been shown that the highest carbon flux to air-breath- ing seabirds in the Southern Ocean occurs within frontal areas (Abrams 1985a). Therefore, zooplankton and seabirds occupy an important position in the Southern Ocean carbon cycle (Huntley et al. 1991). Zooplankton communities in surface waters in the vicinity of oceanic islands, major frontal systems and especially the Antarctic zone have been extensively studied (e.g. Boysen-Ennen et al. 1991; Siegel et al. 1992; Hopkins et al. 1993; Pakhomov 1993; Pakhomov et al. 1994). While the distributions of different groups of zooplankton, along transects carried out between Aus- tralia and the Antarctic continent during the Japanese BIOMASS SIBEX cruise, are documented (Casareto and Nemoto 1986; Iwasaki and Nemoto 1986; Terazaki and Wada 1986; Terazaki 1989), studies dealing with changes in the zooplankton communities throughout the Southern Ocean are still required (Grachev 1991). On a macroscale, a significant correlation has been recorded between the distribution of seabirds and sur- face temperature (Abrams 1985b). Hunt (1991) pointed out that on the mesoscale this correlation is unclear and still under discussion. Oceanographic processes on the mesoscale are more complex and can create hetero- geneous patterns of availability of different prey types that may attract a number of feeding types of predators (Ainley and DeMaster 1990). The main aim of this paper is to provide comparative information on surface zooplankton and seabird abundances and distribution in conjunction with oceanographic features along four