Abundance patterns of infaunal sea anemones and their potential benthic prey in and outside seagrass patches on a Western Australian sand shelf
Abstract:Surface counts and core samples along an intertidal-to-shallow-subtidal depth gradient on a sand shelf bordering the Garden Island shore of Careening Bay, Western Australia, revealed relatively high abundances of the actinarian Heteractis malu and three other rarer infaunal sea anemones. Samples taken in five strata (unvegetated sand at shallow, intermediate and deep water depths; seagrass patches at intermediate and deep water depths) demonstrated that H. malu abundance did not vary significantly with presence and absence of seagrass (Heterozostera tasmanica) but was lower in shallow sand than in other strata, whereas average individual size (volume) of H. malu was smaller in seagrass. Total density and volume of all large (> 3 mm) macrobenthos were greater inside seagrass than in unvegetated sediments, with epifauna exhibiting greater absolute and proportionate differences than infauna. H. malu comprised 26% (ranging from 3% in shallow sand to 59% in deep sand) of the total volume of all large macrobenthos on the flat. H. malu appears to support its high relative abundance with nutrition both from culturing zooxanthellae and from capturing invertebrate prey. A swimming opisthobranch Akera soluta and the blue mussel Mytilus edulis, often as fragments presumably left by predatory crabs and fishes, dominated coelenteron contents in January 1983 and 1984. Low seawater turbidity and warm winter water temperatures promote successful culturing of zooxanthellae, while dense and unrefractory Posidonia australis roots and rhizomes provide necessary attachment surfaces, both contributing to the anomalous sea anemone dominance of this shallow sand shelf.
Document Type: Research Article
Publication date: 1986-05-01
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