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Competitive strategies in soft corals (Coelenterata, Octocorallia). IV. Environmentally induced reversals in competitive superiority

1992; Inter-Research; Volume: 81; Linguagem: Inglês

10.3354/meps081129

1616-1599

P.M. Alino, PW Sammarco, JC Coll,

Ichthyology and Marine Biology

Long-term evidence has demonstrated that an inshore reef (Pandora Reef) in the central region of the Great Barrier Reef, Australia, is becoming increasingly dominated by octocorals.To examlne the effects of the local environmental setting on the outcome of competition for space, pairs of octocoral and scleractinian corals actively competing for space were transplanted from this inshore reef to a n~d-shelf one (Britomart) in a controlled experiment.The 2 areas differ in their physical charac-ter~stics and biological communities.Competition for space between Clavularia inflata (Coelenterata, Octocorallia), Briareum stechei (Octocorallia), and Acropora longlcyathus (Coelenterata, Scleractinia) in all possible pairs was assessed.Controls included undisturbed palred and solo colonies in their natural environment.A second set of corals was relocated to the mid-shelf and returned to its original environment as a control for handling effects.Competitive advantage was est~mated via growth rate.Frequency of overgrowth, tissue necrosis, whole colony mortality, and tissue bleaching were also monitored.In their natural environment, Clavularia and Briareum were competitively superior to Acropora.Briareum was superior to Clavularia.With respect to mid-shelf transplants: the competitive edge of Clavularia over Acropora was reversed; the advantage of Briareum over Clavularia was reduced; and the advantage of Briareum over Acropora remained unchanged.On the mid-shelf, transplanted Acropora and Clavularia controls both suffered high mortality due to increased predation and, in the former, apparently increased light penetration.The growth rate of Briareum increased on the midshelf.Competitive relationships between these species are complex and can be modified by environmental factors.The refuge of the branching coral A. longicyathus on Pandora Reef was its marginally higher growth rate.Most other coral species at the study site, particularly the massives, appear to have succumbed to octocoral growth.Competitive advantage in some octocorals is apparently enhanced in inshore waters of the Great Barrier Reef in the presence of nutrient enrichment and lower levels of predation and light.Changes in local environmental factors in these inshore waters may be contributing to the observed increasing domination of Pandora Reef by octocorals.