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The morphology and population dynamics of Aspidopholas obtecta (Bivalvia: Pholadidae) boring into the Pacific oyster ( Crassostrea gigas ) in Hong Kong
Author(s) -
Wonc P. S.
Publication year - 1982
Publication title -
journal of zoology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.915
H-Index - 96
eISSN - 1469-7998
pISSN - 0952-8369
DOI - 10.1111/jzo.1982.198.4.495
Subject(s) - biology , crassostrea , oyster , larva , pacific oyster , population , bivalvia , metamorphosis , zoology , fishery , ecology , mollusca , demography , sociology
The pholadid shell borer Aspidopholas obtecta Sowerby is a pest of the Pacific oyster ( Crassostrea gigas Thunberg) in Hong Kong. It bores mechanically using the shell as a boring tool. As in other pholads, there are two morphologically distinct adult growth forms: an actively growing form with a strong suctorial foot, and a non‐boring reproductively mature form sealed by a callum. Metamorphosis of the growing to the mature form can occur within one year of post‐settlement and its occurrence increases with the degree of crowding. As the shell grows, it elongates from a round to an oval shape. Size‐frequency analysis showed that the population consists of several age groups with new larval settlement once a year. Spawning occurs in July, and the larvae settle on any available oyster shell, irrespective of age, in August. The annual increment in shell length is about 5 mm and growth takes place throughout the year, but at a lower rate from April to August. This may be the result either of low calcium concentration in the water or of diversion of energy to gonad growth. A high proportion of dead shells was found from May to September and in December and January.