Spatial-temporal influence of hydrological variables on the diversity and abundance of copepods on an equatorial macrotidal beach in the Brazilian Amazon region

Pinheiro, S.C.C.; Leite, N. da R.; Costa, V.B. da; Costa, K.G. da; Pereira, L.C.C, and Costa, R.M. da., 2011. Spatial-temporal influence of hydrological variables on the diversity and abundance of copepods on an equatorial macrotidal beach (Brazilian Amazon). Journal of Coastal Research, SI 64 (Proceedings of the 11th International Coastal Symposium), 425 – 429. Szczecin, Poland, ISSN 0749-0208 Th e aim o f this study was to determine the species composition and abundance of copepods off Ajuruteua Beach, and to verify the effects of specific environmental variables on their occurrence and distribution. Samples were collected monthly from August, 2004, to July, 2005 at three fixed stations. Temperature, pH and salinity were measured in situ. Water transparency was estimated using a Secchi disc. Additional samples of 400 ml of water were collected for the measurement of the concentration of chlorophyll a. Simultaneously, 400 l of surface water were filtered through plankton nets. The data were processed using multivariate analyses. Total rainfall for the twelve-month study period was 1,871.4 mm. Hydrological parameters varied seasonally. A total of 21 taxa were identified, while the presence of copepod eggs and nauplii, and copepodite stages was also recorded. Mean copepod density ranged from 4,000 ind/m³ in July, 2005, to 36,380 ind/m³ in April. The highest densities were recorded during the ebb tide in rainy season months. Euterpina acutifrons and Paracalanus quasimodo were the species with the highest densities. Nauplii and copepodites were recorded throughout the study period. Multivariate analyses revealed a clear separation of the samples between seasons. Copepod abundance correlated with precipitation levels, which in turn contributed to a reduction in salinity during the rainy season due to increased freshwater run-off into local rivers. Local hydrodynamics provoke the mixing of the water column, and the suspension of sediments and organisms located close to the bottom, contributing to the lack of any spatial distribution pattern.