A General Ecology of Bryozoans at Signy Island, Antarctica

Barnes, David Keith Alan (1995). A General Ecology of Bryozoans at Signy Island, Antarctica. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000fb94

Abstract

This study set out to investigate a broad range of ecological aspects in Antarctic bryozoans, including distribution, feeding, growth and predation, and how these were influenced by environmental conditions. A number of sites, at a variety of depths, were chosen from within Borge Bay, Signy Island in the South Orkneys, using SCUBA. Some of these studies atempted to monitor populations in situ over tlie course of two years, mainly with the aid of underwater cameras.

Photographic samples were taken on three vertical transects of 5.5 m rock faces and two 40 m sloping transects. The percentage cover of substratum ranged from 0-100% and the colonising communities included representitives of 10 phyla. Ice impact, depth and profile were important influences on community cover and composition. Collections of up to 200 rocks were made from each of six localities ranging from the intertidal to 42 m. Area colonised, number of colonising phyla, bryozoan species and colonies were all found to increase with substratum surface area and depth. Over 4000 competitive interactions between bryozoans were recorded, which indicated the presence of a competitive hierarchy with one ultimately dominant species. Colonisation of artificial substrata was very slow comparative to that found by similar temperate studies and suggested an essentially classical successional pattern of colonisation. Bryozoans were abundant on the externa of a variety of other macroinveitebrates, including fouling the surfaces of erect bryozoan species.

Lophophore activity (feeding) occurred for most of the year in the bryozoans monitored, and environmental cues were suggested for the changes in activity of some species. Growth was generally slow but contrasted strongly in duration between the monitored species. The growth checks, formed annually by one species, showed interannual variations in growtli throughout the population. Two bryozoan species had specific nudibranch predators, though their populations seemed little influenced by predation.

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