Abstract
Beds of the ascidian Pyura stolonifera on rocky shores around Sydney, Australia, provide an important habitat for many organisms, such as algae, chitons, limpets and snails. Fishermen collect Pyura for bait, which can change the structure of those beds. This may, in turn, cause changes in their associated biota. To predict the effects of such disturbances, it is necessary to understand the relationship between the structure of the habitat provided by beds of Pyura and their associated assemblages. Beds of Pyura can provide two types of habitat: Clumped, with >50% cover of closely packed individuals or Sparse, with <50% cover, where individuals are mostly isolated from contact with others. The spaces amongst the Pyura can be bare rock or rock covered by numerous species of algae and sessile animals. Nineteen algal species and 45 species of animals were identified in the field in Clumped and Sparse habitats. Assemblages differed significantly between patches of Clumped and Sparse habitat and much of the difference was attributable to relatively few species. In addition, a number of species of algae and animals live on the surface of the Pyura themselves. Eighty-four taxa were found at the scale of individual Pyura, many of which were relatively small and cryptic. Organisms on Pyura differed between individual ascidians that were isolated from other Pyura (i.e. a more common situation in Sparse habitat) and those that were surrounded by and in contact with other Pyura (i.e. more common in Clumped habitat). These differences were mostly attributed to a few families of small molluscs. It appears that changes in the structure of beds of Pyura have the potential to make significant alterations to intertidal assemblages at the scale of individual Pyura and at the scale of the habitats formed by beds of Pyura.
Published Version
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