Modeling oyster populations II. Adult size and reproductive effort.

A time-dependent model of energy flow in post-settlement oyster populations is used to examine the factors that influence adult size and reproductive effort in a particular habitat, Galveston Bay, Texas, and in habitats that extend from Laguna Madre, Texas to Chesapeake Bay. The simulated populations show that adult size and reproductive effort are determined by the allocation of net production to somatic or reproductive tissue development and the rate of food aquisition, both of which are temperature dependent. For similar food conditions, increased temperature reduces the allocation of net production to somatic growth. An increase in food supply generally results in increased size as more energy is used in somatic growth; however, at low latitudes, as food supply increase, adult size decreases because the allocations of more net production to reproduction outweighs the effect of increased rates of food aquisition. Variations in temperature and food supply affect reproductive more than adult size because the rate of energy flow through the oyster is higher in warmer months when most net production is allocated to reproduction and small changes in temperatute substantially change the spawning season. The wide range of reproductive effort expected from small changes in temperature and food supply suggest that comparisons of adult size and reproductive effort between oyster populations can only be made within the context of a complete environmental analysis of food supply and associated physical parameters and an energy flow model.