POPULATION RECOVERY OF THE SEA-URCHIN LYTECHINUS-VARIEGATUS IN A SEAGRASS FLAT (ARARUAMA LAGOON, BRAZIL) - THE ROLE OF RECRUITMENT IN A DISTURBED ENVIRONMENT

The size, structure, and density of a population of Lytechinus variega tus were recorded from a shallow seagrass bed (Halodule wrightii) at 4 0-day intervals from April 1994 to April 1995. A local mass mortality was observed in May 1994. The density declined from 0.57+/-0.10 to 0.0 6+/-0.05 ind.m(-2), mean size declined from 37.6+/-0.49 to 16.2+/-2.14 mm and maximum size from 75 to 40 mm. Ten months after mortality, the maximum and mean sizes had returned to initial values, but density ha d not (0.10+/-0.03 ind.m(-2)). A second, smaller mass mortality occurr ed in April 1995. High values of gonad index were recorded before mort ality (9.40+/-5.97) and after population recovery (11.96+/-5.74). Recr uitment was continuous throughout the year, but reached a peak from Au gust to October. This can be related to the patterns of upwelling in t he region. Mass mortality is probably an annual event in this populati on that can be correlated with the occurrence of low tides during dayt ime in the fall. The population can recover during the summer when low tides occur during the night. The massive input of recruits prevents extinction of the population during the season of high mortality. Popu lation recovery depends on the magnitude of recruitment.