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 detennined by the allocation of net production to somatic or reproductive tissue development and the rate of food acquisition, both of which are · temperature dependent. For similar food conditions, increased temperature reduces the allocation of net production to somatic tissue and increases the rate of food acquisition. This temperature effect, however, is mediated by changes in food supply. Within the Gulf of Mexico, oyster size declines from north to south because increased temperature deer.eases 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 increases, adult size decreases because the allocation of more net production to reproduction outweighs the -effect of increased rates of food acquisition. Variations in temperature and food supply affect reproductive effort more than adult size because the rate of energy flow through the oyster is higher in wanner months when most net production is allocated to reproduction and small changes in temperature 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.