An ecological study of epibionts associated with the shell of the sea scallop, Placopecten magellanicus (Gremin, 1791) (mollusca- pelecypoda)

Barnes, David Hugh (1974) An ecological study of epibionts associated with the shell of the sea scallop, Placopecten magellanicus (Gremin, 1791) (mollusca- pelecypoda). Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The object of the study was to describe the assemblage of epibiotic organisms associated with the shell of the sea scallop, Placopecten magellanicus (Gmelin, 1791). Qualitative information from approximately 3 dozen shells was combined with quantitative data obtained from 12 additional shells. The numerical data were subjected to statistical analyses in order to examine dominance, diversity and affinity within the association. -- Live scallops were collected by divers from an area in St. Mary's Bay, on the southeast coast of the Island of Newfoundland. The external surfaces of the shells were examined using a dissecting microscope and the area occupied by each epibiotic species was measured. X-radiography was used to investigate the effects of boring species within the shells. A total of 74 epibiotic species of animals and plants was recorded. -- The affinity studies revealed that the scallop shell supports an epibiotic community consisting of separate and distinct component communities on its upper and lower valves, each having a predictable species composition. No seasonal or depth-related effects were detected regarding the community on adult scallops over 10 years of age, but the structures of the associations on young scallops (2 and 3 years old) were different in several respects from the adult shell community. -- The dominant species are sessile or sedentary in habit and are either filter- or deposit- feeders. They are not obligate members of the community, but nevertheless reproduce and in some cases complete their entire life cycle within the community. Diversity indices obtained for the community were generally low (ranging from 0.3 to 3.6 for a single valve) and were lower for upper valves than for lower valves. -- Boring species play an important role in the development of the community. Their activities modify the surface of the shell, making it more habitable for certain later-arriving species. Damage to the shell is rarely extensive and the scallop does not generally appear to suffer any harm from the presence of these or any other of the epibionts.

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