Competition, mortality and diversity in South Atlantic coastal boulder communities |
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Authors: | David K A Barnes Clare Lehane |
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Institution: | (1) Department of Zoology and Animal Ecology, University College Cork, Lee Maltings, Cork, Ireland e-mail: dkab@ucc.ie; Fax: +353-21-270562, IE |
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Abstract: | Boulder shores are common at all latitudes and dominate the intertidal and subtidal zones of sub-Antarctic coastlines. The
encrusting benthos of boulders was examined on similar shore types at four locations: Tierra del Fuego, East Falkland, West
Falkland and Bird Island (off South Georgia). Bird Island is unusual in experiencing high trampling and organic enrichment
from fur seals. The results were compared to a Patagonian site and a non-trampled South Georgia site (Husvik) and other sites
taken from the literature. Principal Component Analysis revealed South Atlantic/Southern Ocean encrusting faunas formed a
distinct cluster when compared to assemblages from elsewhere at similar latitudes. Bray Curtis cluster analysis of the South
Atlantic-Southern Ocean sites showed the major division was between Southern Ocean and South Atlantic Ocean sites, beyond
which there were three distinct clusters centred around Patagonia (Magellanic), the Falklands and Southern Ocean sites. The
organisation of competitive interactions between species was mostly determinate and transitive (essentially hierarchical).
The transitivity index scores were higher than most similar assemblages studied to date. The diversity of encrusting assemblages
ranged from Shannon Weaver H values of 2.38–0.77 (East Falkland and Bird Island, respectively) in the intertidal to 1.27–0.73 (Patagonia and South Georgia,
respectively) in the subtidal zone. Annual mortality (of bryozoan colonies) varied from 85–97% in the intertidal to 65–92%
in the subtidal, being higher in the Southern Ocean than South Atlantic sites, largely due to ice scour and wave action. The
Bird Island mortality values may be high even for a Southern Ocean site.
Accepted: 5 October 2000 |
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