MEPS 124:117-128 (1995)  -  doi:10.3354/meps124117

Aspects of reproduction associated with the use of a segmented regression to describe the relationship between body weight and shell length of Mytilus edulis

Salkeld PN

Data on total dry tissue weight and shell length were obtained from an intertidal population of Mytilus edulis located in an estuary in SW England. Representation of the log10 transformed data is significantly improved by the use of a segmented regression instead of a single linear regression. There is a significant reduction in the slope (b) of the regression, relating total dry tissue weight (y) to shell length (x), for mussels over 50.3 mm. This pertains also to the component tissues: mantle (at 50.1 mm shell length), digestive gland (at 60.4 mm) and remainder (at 52.7 mm). Weight of mantle tissue and of digestive gland does not change (b = ca 0), whilst remaining tissue increases, but at a reduced rate, as shell length increases in excess of these respective sizes. Stereological examination of sections of mantle tissue were made throughout the year. Results indicate that high levels of reproductive tissue (i.e. >80% of mantle volume) are achieved in half as many large individuals (mean shell length 64.7 mm) as in 2 smaller size groups (means of 35.1 and 50.4 mm). These results suggest that reproductive effort increases to a maximum at a shell length of approximately 50 mm, thereafter declining as size increases. A segmented regression is also appropriate to describe the relationship of total tissue and mantle tissue weight to shell length of a sample from another estuarine population, but not from a wave exposed, open shore population. Reasons for these observations are discussed in the context of the feeding:metabolism ratio, availability of food and age.

ÝMussels . Mytilus edulis . Size . Length . Weight . Age . Allometry . Reproduction . Segmented regression

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