(Shumway, 1996). Powell et al. (1992) reviewed the literature on filtration rates for numerous marine bivalves and found that the relationship between filtration rate and size was similar for all species examined, including several oysters.
Oysters do not regulate their body temperature or the salinity of their body fluids; thus, their metabolic activity is closely tied to the temperature of their surroundings, and the salt content of their blood is the same as that of the ambient water (Shumway, 1996). The ability of oysters to tolerate different environments is species specific. For instance, the European oyster, Ostrea edulis, grows in relatively cool, clear, water of high salinity (Yonge and Thompson, 1976). Crassostrea species, in contrast, are more typically inhabitants of estuaries in which they tolerate wide fluctuations in temperature, salinity, and turbidity.
The oyster’s energetic investment in reproduction is prodigious, with individual females capable of producing many millions of eggs. Oysters typically become reproductively mature as males and may become female in subsequent seasons. Reproductive activity is seasonal and in temperate regions is generally dictated by temperature. Spawning occurs predominantly during the warm season, although other factors, such as phytoplankton blooms, may also play a role. Members of the genus Crassostrea shed their gametes directly into the water where fertilization occurs, and larval life is spent entirely in the water column. In contrast, fertilization and partial larval development in Ostrea take place in the interior of the oyster’s shell. Females release eggs within the shell cavity, and fertilization occurs when sperm shed by nearby male oysters get drawn into the female cavity. The larvae develop partially among the female’s gill filaments, which turn dark and become gritty as the larvae produce shells and become pigmented. The female’s unpleasant appearance and texture at this time are the principal reason that eating Ostrea species is avoided in the summer (months without “R,” or May through August) when reproduction occurs. The larvae of Ostrea species are eventually expelled from the female’s shell cavity and complete their development in the water column. Oysters that are brooders produce smaller numbers of offspring than nonbrooders.
The waterborne larval stage of oysters allows them to disperse from the immediate site of the parental stock, enhances genetic mixing, and allows the colonization of new locations. The larvae are both dispersed and concentrated by water currents and wind. At the end of the larval life, usually 2 to 3 weeks, the oysters “set.” Unlike clams, which can settle into mud and can shift around as adults, oyster larvae cement themselves to a clean, hard substrate and lose their mobility (Yonge and Thompson, 1976). The substrate may be another oyster, a piece of shell, a pebble, a tree root, or any other solid, clean surface. The concentrating effect of wind and