HOW LONG DOES OYSTER SHELL LAST ON AN OYSTER REEF?

A reduction in population abundance brought on by an unprecedented 6 years of low recruitment has reduced shell input through natural mortality on Delaware Bay oyster beds. Quantitative stock surveys provide an estimate of surficial shell over the same time period, permitting the reconstruction of the time history of shell since 1998 and estimation of the rates of shell addition and loss. Shell loss rates were surprisingly high. In most cases, half of the shell added to an oyster bed in Delaware Bay in a given year is lost over a subsequent period of 2 to 10 years. The expectation that the half-life of shell would be lowest at higher salinities where boring sponges and other epibionts are prevalent was not the case. The shortest half-lives, typically two to three years, are at intermediate salinities. Half-lives increase to about ten years both upbay (lower salinity) and downbay (higher salinity). Minimal shell doubling times were calculated under the assumption of no shell loss, a maximum accretion rate. They varied from somewhat less than ten to more than twenty years. This indicates that shell has the potential to accumulate rapidly on human time scales although this is not so fast given oyster generation times. The lack of shell accumulation in terms of reef vertical accretion or lateral expansion of oyster reef in Delaware Bay can be explained if most shell produced yearly does not long remain recognizably intact. Shell, at least in estuarine habitats, may have low preservation potential even in areas that, when preserved, will appear to be shell beds. Shelliness does not necessarily imply good preservability.