Small scale spatial distribution of oysters (Crassostrea virginica) on oyster reefs.
The small-scale spatial distribution of oysters was examined on 11 reefs in the Copano Bay - Aransas Bay area of the Texas coast. Small oysters (<= 2cm) were contagiously distributed (s^2/x > 1) and positively spatially autocorrelated; that is, small oysters were patchily distributed. Patch size ranged up to about 40 cm. Large oysters (> 5 cm) were less contagiously distributed and normally were negatively spatially autocorrelated; that is the number of large oysters on adjacent clumps tended to differ more (many vs. few) than would be expected by chance. Negative spatial autocorrelation was restricted to adjacent clumps < 12 cm apart. Consequently, as the oyster populations aged, their spatial distributions changed. The spatial distribution of large oysters on nearby clumps was affected by the number of large oysters distributed among the clumps. As the variance-to-mean ratio increased, the populations became more negatively spatially autocorrelated. Consequently, large oysters affected the survivorship of oysters on adjacent clumps. Mortality, produced perhaps by predation and disease, modulated by competition for food affecting the oyster's susceptibility to mortality, could explain these changes in distributional pattern.