STRUCTURE AND SEASONALITY IN A MALAYSIAN MUDFLAT COMMUNITY

An assessment of community composition and the functional roles of the dominant species was carried out in 2 intertidal areas of Malaysian mudflat dominated by natural populations of the arcid bivalve mollusk Anadara granosa. In addition to A granosa, organisms of numerical importance were the venerid bivalve Pelecyora trigona, the neogastropod Plicarcularia leptospira, the mesogastropods Stenothyra glabrata and Cerithidea cingulata and the hermit crab Diogenes sp. The mesogastropod Natica maculosa and the neogastropod Thais carinifera may be of some importance to community organization but they are not numerically dominant. Annelids are conspicuous by their absence. The following trophic roles were ascribed to specific members of the community: A. granosa, facultative surface deposit feeder; P. trigona, suspension feeder; P. leptospira, scavenger; C. cingulata, deposit feeder/grazer; S glabrata, deposit feeder/grazer; N. maculosa, predator; T carinifera, predator; Diogenes sp. scavenger/predator. S. glabrata is of particular interest because it appears to fill the niche occupied by mud snails of the genus Hydrobia in temperature mudflat systems. There is evidence of seasonality on the mudflats which points to a spawning of certain forms triggered by the major annual salinity depression at the time of the onset of the north-east monsoon in Oct./Nov. Concentrations of benthic chlorophyll a showed no obvious signs of a seasonsal fluctuation and the seasonality of the primary consumers is not though to be related to food abundance. There is some evidence of seasonality of reproduction in N. maculosa which preys on the seasonally reproducing bivalves.