Community structure of estuarine meiobenthos

Abstract

Meiofaunal samples were collected from intertidal mudflats in the lower, middle and upper reaches of the Tamar estuary, South West England in April and October, 1982. Species abundance and biomass patterns of nematodes and copepods did not follow the expected trends in relation to salinity: the lowest species diversity (below neutral model predictions), the steepest ranked species abundance curves and the greatest departure from the theoretical lognormal distribution of numbers and biomass of individuals among species were found at the middle rather than the upper site. Huston's (1979) dynamic equilibrium hypothesis is invoked to explain these phenomena, but the hypothesis remains to be tested. Intense macrofaunal predation and disturbance, together with more pronounced environmental fluctuations, may eliminate competitive exclusion at the upper site resulting in a relatively high species diversity. The absence of such population reduction mechanisms at the middle site results in competitive exclusion and lowered diversity. The major nematode species at the upper site have certain opportunistic characteristics, and at the middle site conservative characteristics, which support the contention that these are respectively successional and climax communities. The lower site may represent an intermediate successional stage with the highest diversity. The apparent correlation between the abundances of 3 copepod and 1 nematode species with changes in salinity at the middle and upper sites between April and October is thought to result from passive suspension and transport of these species upstream during the summer: there is a distinct fine-scale vertical stratification of species in the sediment at the middle site, with the species in question having an extreme surficial distribution.