Austral Ecology (2006) 31, 656–666 doi:10.1111/j.1442-9993.2006.01618.x © 2006 Ecological Society of Australia *Corresponding author. Accepted for publication December 2005. Ecological contrasts across an Antarctic land–sea interface CATHERINE L. WALLER,* DAVID K. A. BARNES AND PETER CONVEY Natural Environment Research Council, British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 0ET, UK (Email: cathw@bas.ac.uk) Abstract We report the composition of terrestrial, intertidal and shallow sublittoral faunal communities at sites around Rothera Research Station, Adelaide Island, Antarctic Peninsula. We examined primary hypotheses that the marine environment will have considerably higher species richness, biomass and abundance than the terrestrial, and that both will be greater than that found in the intertidal. We also compared ages and sizes of individuals of selected marine taxa between intertidal and subtidal zones to test the hypothesis that animals in a more stressed environment (intertidal) would be smaller and shorter lived. Species richness of intertidal and subtidal communities was found to be similar, with considerable overlap in composition. However, terrestrial communities showed no overlap with the intertidal, differing from previous reports, particularly from further north on the Antarctic Peninsula and Scotia Arc. Faunal biomass was variable but highest in the sublittoral. While terrestrial communities were depauperate with low biomass they displayed the highest overall abundance, with a mean of over 3 × 10 5 individuals per square metre. No significant differences in ages of intertidal and subtidal individuals of the same species were found, with bryozoan colonies of up to 4 years of age being present in the intertidal. In contrast with expectation and the limited existing literature we conclude that, while the Antarctic intertidal zone is clearly a suboptimal and highly stressful habitat, its faunal community can be well established and relatively diverse, and is not limited to short-term opportunists or waifs and strays. Key words: biodiversity, biomass, desiccation, environmental stress, freezing, intertidal, subtidal, terrestrial. INTRODUCTION Adjacent terrestrial and marine ecosystems contrast sharply throughout the global coastline, but at polar latitudes both similarities and differences are par- ticularly striking. Organisms on land and in the sea both experience extreme and chronic low tempera- tures, varying periods of ice and/or snow cover and, on an annual, timescale the maximum possible varia- tion in light climate. While the final of these points applies equally to both polar regions, at comparable latitudes the first two reach greater and more pro- longed extremes in the Antarctic than the Arctic (Dayton 1990; Convey 1996a; Danks 1999) such that virtually all of the terrestrial environments of the Ant- arctic continent, and much of the surrounding ocean, have no close comparisons in the Arctic. Antarctic marine life is rich and diverse, at species through to phylum levels (see Arntz et al. 1994; Brey et al. 1994; Clarke & Johnston 2003) with high levels of endemism (Arntz et al. 1997), in contrast with the small pockets of seasonally ice- or snow-free land, which are populated by depauperate communities including only a few higher taxa, such as mites, col- lembolans, nematodes and tardigrades (Bergstrom & Chown 1999; Convey 2001; Convey & McInnes 2005). Marine species experience only tiny fluctua- tions in temperature and other factors such as salinity (see Clarke et al. 1988), are typically highly stenother- mal (Pörtner et al. 2001; Peck 2002) and generally face relatively small seasonal changes in energetic demand (Lehtonen 1996; Fraser et al. 2002). Virtually the reverse is true for terrestrial habitats, which may experience 20°C or greater change in temperature in a day, and up to 80–100°C variation over the annual cycle, often including transgressions of the 0°C freez- ing boundary (Smith 1988; Convey 1996b). Species here are faced with rapid and often unpredictable alternation between periods of torpor and activity (Burn 1984; Worland & Convey 2001). In comparison with the lower latitude environments that are inevitably most familiar, Antarctic marine and terrestrial habitats appear to illustrate one end point of the extremes available on the planet. However, to date most polar ecologists have paid little attention to the boundary or interface between the two. Superficial consideration quickly suggests that the intertidal zone has the potential to suffer from the worst of the con- ditions already described above. Furthermore, organ- isms living in the intertidal may experience salinity as low as 12 PSU (‰) due to freshwater runoff, possibly even lower if submerged in a melt stream, exposure to air temperatures which may vary by 20°C during exposure in the tidal cycle, and the devastating distur-