Population aspects of Tagelus plebeius (Mollusca: Bivalvia: Solecurtidae) in the Ceará River estuary, Ceará State, northeast Brazil

Abstract

This research work was designed to evaluate the population density and dispersion pattern of Tagelus plebeius in the Ceará River estuary, Ceará State, correlating these parameters to seasonal variations in temperature, salinity, rainfall and sediment characteristics in that area. Samples were collected monthly from May, 2006 to June, 2007, in diurnal spring tides. The temperatures of air, water and sediment did not change significantly during the study period, and there were no significant changes in granulometric composition. The bed was constituted by fine sand, with a predominance of silt-sand grain size. T. plebeius are randomly distributed along the study area, with maximum monthly average density of 41.2 ind.m-2 (December, 2006) and a minimum of 4 ind.m-2 (September, 2006). The correlation analysis also showed that rainfall has a strong influence on the distribution pattern of bivalves. It is probable that organisms tend to aggregate in more distant areas of the edge of the bed in order to reduce osmoregulatory effects of decreased salinity during this period, as well as increased river flow have changed the disposition of the bed, which can have promoted the aggregation of organisms.