The partitioning of energy between growth and reproduction in the giant scallop, Placopecten magellanicus (Gmelin)

MacDonald, B.A. (1984) The partitioning of energy between growth and reproduction in the giant scallop, Placopecten magellanicus (Gmelin). Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Populations of the giant scallop Placopecten magellanicus were collected from different water depths at several locations in Newfoundland. The major objective of this study was to determine whether growth and production differed between populations and, if so, whether such differences were attributable to food availability and temperature regimes. Population reproductive characteristics such as the annual cycle of gametogenesis, fecundity, reproductive effort, and reproductive cost were also measured to determine if they were directly influenced by environmental variables. -- Additional information was obtained by examining scallops from New Brunswick and New Jersey to determine whether growth and reproductive characteristics are altered by conditions such as temperature known to vary with latitude. Scallops grown in suspended culture provided an opportunity to study age related growth and reproduction in a population of Placopecten magellanicus introduced to a more favourable but somewhat artificial environment. -- More rapid shell growth rates greater somatic and gamete production, and higher reproductive effort values were recorded for populations growing under more favourable conditions of food and temperature associated with shallow water and suspended culture conditions. Clearance rates and metabolic rates were well correlated with seasonal changes in environmental variables. Estimates of reproductive cost suggested that populations P.magellanicus from Newfoundland are generally restrained in their reproductive patterns. - Local environmental conditions strongly influenced production estimates. This is especially important in any consideration of geographical trends in growth and reproductive characteristics, as the presence or absence of such trends appeared to depend on which characteristic was compared and the methodology used. Scallops from Newfoundland grew as fast as those collected from more southerly locations and were more productive especially when the apparent temperature advantage available to the latter populations was taken into account.

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