The ecological strategies of algal species in a predominantly red algal community at 15 m depth oh a high energy coast of southern Australia are described. The three determining conditions for this community are considered to be competition, stress and disturbance, and they each invoke a distinctive strategy, namely dominance, adaptation to low light, and the ephemeral strategy respectively. A triangular ordination is used to model the relative importance of these strategies for common species during a successional sequence and in the mature community. During the succession there is a shift from ephemeral species to dominant species, while species adapted to low light appear only in the late succession. Some species have composite strategies that are less easily modelled. They are species with heteromorphic life histories, and those which depend on vegetative reproduction. Introduction The dynamics of the maintenance of marine benthic plant communities are complex and may involve interspecific competition as well as successional phenomena. To understand the processes by which many species manage to coexist in a community despite the tendency for a few strongly competitive species to oust the others, it is necessary to examine their ecology and life history strategies which have envolved in their particular environment. This will usually require detailed and tedious observations at a site for a prolonged period and sometimes experimental manipulations in the community. Three ecological strategies of benthic algae have been recognized; they are dominance, adaptation to low light, and the ephemeral* strategy (Foster 1975, Dayton 1975); others such as Uttler and Littler (1980) have recognised only two strategies — dominance and opportunism*. * There is no unanimity in terminology for this strategy and the terms ruderar, Opportunistic* and fugitive' have all-been used (see Hutchinson 1951, Grime 1974, Dayton 1975). In recent papers on terrestrial grasslands Grime (1974, 1977) has elaborated the theory underlying these strategies by defining their determining conditions and by developing a model to illustrate their relations. The application of this model to a benthic algal community in South Australia is explored in this paper. The study site is situated at 15 m depth about 1300 m off Cape Northumberland, South Australia (Lat. 38°3'30S, Long. 140°37'l5E) on a substrate of aeolianite limestone, and is subject to a strong prevailing south-westerly swell creating a powerful underwater surge on the bottom. The benthic algal community at the study site includes more than 200 species, consisting of five common species of dominant red algae up to 40 cm high, an understorey of about 30 common species mostly of red algae; the remaining 165 or so species are all quite rare. Grazing in the community was insignificant. The study involved an investigation of the abundance and distribution of species, their growth, reproduction and longevity and their relations with the environmental factors water movement and light, and finally a series of experiments to determine the algal succession in the community (Shepherd 1979). 0006-8055/81/0024-457$02!00 © by Water de 'Gruyter & Co. · Berlin ' New York Unauthenticated Download Date | 4/12/16 6:03 AM 458 Shepherd: Ecological strategies in red algal community