Benthic community development in Antarctica: recruitment and growth on settlement panels at Signy Island

Abstract

Identity, quantity and seasonal variation in recruiting invertebrate larvae were investigated at Signy Island, Antarctica. Nine settlement panels were deployed at each of three sites at depths ranging between five and 25 m over a two year experimental period. Longer-term community development was followed using three panels continuously immersed for up to 21 months at each site, with monthly photographs taken in situ. Shorter-term variations in recruitment were studied by regular replacement of triplicate panels, which enabled the measurement of seasonality of recruitment onto artificial substrata in Antarctica, for the first time. Cyclostomatid and cheilostomatid bryozoans, and spirorbinid polychaetes were the dominant colonising taxa both in terms of numbers and area covered. Very low rates of colonisation were observed: <2% of the panels at 5 m, and <6% of the panel areas at 25 m, were covered after 15 months. Whilst little seasonality of recruitment was observed in spirorbinids, that of cheilostomatid bryozoans showed a significant peak between June and February. Successful recuitment levels of colonising taxa suggested seasonal and interannual variation, although not conclusively. Measurement of growth of individual bryozoan colonies was assessed by image analysis of the in situ monthly photographs. Mean growth ranging between 1.7 mm 2 ( Lacerna eatoni) and 7.1 mm 2 ( Arachnopusia inchoata) per month were recorded. There was considerable inter- and intra-specific variation of growth of the encrusting cheilostomatid species investigated and this is the first report of such measurements having been made in Antarctica.