The Growth and Life-History Strategy of the Soft-Shell Clam, \u3cem\u3eMya arenaria L.\u3c/em\u3e

The growth and life-history strategy of the soft-shell clam, Mya arenaria were analyzed through the exanination of 25 populations spread throughout the species\u27 geographic range. Growth rate was determined by length-frequency analysis and was analyzed using Gallucci and Quinn\u27s ω parameter of the von Bertalanffy equation. Principal components analysis (PCA) was used to analyze environmental variability. Variations in growth were related to environmental differences. Growth varied inversely with latitude. This relationship was due mostly to temperature differences. PCA indicated that several environmental factors varied systematically with latitude. Growth was found to be negatively correlated to the siltiness of the sediment and to the concentration of sedimentary hydrocarbons. Distinct shifts in growth rate occurred when environmental quality was significantly altered by a discrete pollution event. Growth was reduced in response to heavy metal effluents and oil spills. Fairly rapid recovery followed heavy metal pollution abatement. Recovery at oil spill sites was variable but slow. The relationships between various life-history parameters were analyzed to elucidate the species\u27 modes of adaptation and life-history strategy. Within the context of latitude variations in the environment an association was found between decreasing latitude and: faster growth, greater variation in juvenile mortality, larger maturation size, larger egg size, lower egg density and decreasing longevity. These relationships indicated that M. arenaria follows a bet-hedging life-history strategy. On a local scale a positive relationship was found between larger egg size and greater egg density. This trend appeared to be associated with the condition of the population and may represent a physiological response to local environmental conditions. The proportion of females (52%) was found to be significantly greater than the proportion of males. No evidence of a mechanism behind this disparity was detected