Antarctic sessile marine benthos: colonisation and growth on artificial substrata over three years

The development of sessile invertebrate assemblages on hard substrata has been studied extensively in temperate and tropical latitudes. Such studies provide insights into a range of ecological processes, and the global similarity of taxa recruiting to these assemblages affords the potential for regional-scale comparisons. However, few data exist for high latitude assemblages. This paper presents the first regularly resurveyed study of benthic colonisation from within the Antarctic Circle. Acrylic panels were deployed horizontally on the seabed at 8 and 20 m depths at each of 3 locations in Ryder Bay, Adelaide Island, SW Antarctic Peninsula (67 degrees 35'S, 68 degrees 10'W). Assemblages colonising upward- and downward-facing panel surfaces were photographed in situ from February 2001 to March 2004. Assemblages were dominated by bryozoans and spirorbid polychaetes. Total coverage after 3 yr ranged from 6 to 100 % on downward-facing surfaces but was < 10 % on all upward-facing surfaces. Overall colonisation rates were up to 3 times slower than comparable temperate latitude assemblages but showed unexpected similarities with a tropical assemblage. Growth in most taxa was highly seasonal and maximum growth rates of encrusting bryozoans were 5 to 10 times slower than literature values for temperate species, suggesting rate limitation by cold rather than food availability. Assemblage development was controlled predominantly by post-settlement disturbances, and there was considerable variability between locations associated with differences in disturbance history. Ice impact was significant only at 8 m but biotic disturbances exerted a stronger and more consistent influence on assemblage development at all sites. It is suggested that the combination of slow growth rates and strong environmental seasonality results in succession being more predictable than in comparable temperate or tropical assemblages.