Settlement, growth and production of the mussel Mytilus galloprovincialis

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Abstract
Abundance, growth, survival and production of M. galloprovincialis Lamk. were investigated in a subtidal bed on the muddy bottom of a deltaic lagoon of the Adriatic coast (Italy) from 1977-1979. Observations on recruitment timing were integrated by checking larval settlement on semiartificial substrata during 1980. Reconstruction of the cohort composition of the mussel-bed population was derived from size-class analysis of samples. The Bertalanffy growth curve was fitted on size-class data. Incorporating temperature as day-degrees into the length-growth curve, and using the results of length/dry weight conversions, estimates were made of seasonal variations in weight. Mortality rates were estimated from density variations of cohorts. Settlement shows a fairly well defined seasonal pattern with a May-June peak, following the main late winter spawning of mussel populations of that region. Individual length growth is rapid, reaching 50.0 mm in .apprx. 14.5 mo. after settlement. Weight growth shows large seasonal variations mainly due to winter spawning and starvation. Mortality rates are higher for old, larger mussels, year round, and for all specimens during spring-summer. Annual production, starting from 0+ recruits surviving in autumn after settlement, was estimated from 0.30-0.53 kg m-2 of dry flesh weight. Both growth and production probably benefit from abundant food in the environment but get hindered mainly by the excessive amount of suspended inorganic detritus coming from the deltaic river branches, which interferes with the mussels'' efficiency in absorbing useful food and causes heavy mortality.

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