Population parameters of Sagitta friderici Ritter-Záhony (Chaetognatha) in the surf zone of Cassino Beach, South of Brazil

Abstract

An analysis was carried out of 36 samples of zooplankton obtained between 10th October 1990 and 24th April 1992 at a station close to the mouth of the Lagoa dos Patos estuary (32º9’S - 52º18’W) located in the surf zone of Cassino beach. Data on density, biomass, size variation and frequency distribution of the development stages the Chaetognatha Sagitta friderici were obtained, in order to determine the population characteristics of this major predator in the zooplankton pelagic chain. The population of S. friderici presented three density peaks during the year, and a size variation during the different development stages which reflected the variations in water temperature. Three cohorts were identified over the year, based on the occurrence of developmental stage 4 (mature adults), followed by stage 0 (juveniles) in the samples. Development took 73 days for the Spring/Summer cohort, 95 days for the Summer/Fall and 136 days for the Fall/Spring. The population of S. friderici of the surf zone of Cassino beach, in the South of Brazil, presented similar characteristics with Cananéia estuary population, in the coastal area of São Paulo.