Estimation of Taylor's Power Law parameters a and b for tidal marsh macrobenthic species.

Abstract

In the Cananeia region of southeastern Brazil, Spartina alterniflora marshes colonize tidal flatsfringing mangrove woodlands and displaying a zonation typical of monocultures. The pattern observed can be explained by the combined effects of organism resistance to emersion and physical dependence on the plants as habitat. In this context, it is interesting to quantify the aggregation index for the dominant species associated with the salt marsh. A tool which enables us to do it is Taylor´s power law, which combines the mean and the variance distributions of species in a known area. From August 1988 to January 1989, tenrandom samples were taken monthly from the lower and upper marshes using a 20 cm diameter corer (0.03 m2) at a depth of 10 cm. The five most representative species of the system were selected for further analysis, and for each of these, Taylor´s power law parameters were calculated. Epifaunal species present aggregation indexes approaching randomness. The aggregation indexes for the infaunal species were observed to have consistently high values even in clearly different conditions of population density and availability of organic matter. The smaller number of infauna forms in the lower marsh as compared to the upper marsh does not point to a competitive disadvantage since there is no alteration in b values. For the infauna species only, the value of a shows a sharp decrease from the lower to the upper marsh.