Effects of seasonality on zooplankton community dynamics in the macrotidal coastal zone of the Amazon region

Costa, K.G. da, Pinheiro, P.R.S., Melo, C.A.R., Oliveira, S.M.O. de, Pereira, L.C.C. and Costa, R.M. da, 2011. Effects of seasonality on zooplankton community dynamics in the macrotidal coastal zone of the Amazon region. Journal of Coastal Research, SI 64 (Proceedings of the 11th International Coastal Symposium), 364 - 368. Szczecin, Poland, ISSN 0749-0208 In order to understand zooplankton composition, as well as the effects of hydrological variables on its dynamic, nycthemeral samples of hydrological and biological variables were collected bimonthly between February and December, 2008, at a fixed station off Ajuruteua Beach (Northern Brazil). Temperature and salinity were measured using a CTD, while pH and dissolved oxygen were determined through the analysis of water samples. Zooplankton samples were obtained through the filtration of 200 L of water using plankton net (120 pm mesh size). After the identification, zooplankton density and diversity were determined. Data were analyzed using a one-way ANOVA, K-dominance curves and non-metric multidimensional scaling. Temperature and salinity were higher during the dry season, ranging from 19.67 +/- 0.44 degrees C in April to 29.22 +/- 0.75 degrees C in August and from 25.76 +/- 0.23 psu in June to 36.68 +/- 0.02 psu in December, respectively. The pH levels also varied significantly between 7.33 +/- 0.12 in February to 8.41 +/- 0.14 in October. Oxygen concentrations were lowest in December (5.56 +/- 0.41 mg/L), and highest in August (8.10 +/- 0.42 mg/L). Forty eight taxa were identified, 48% of which were copepods. The other 52% included other groups such as Bivalvia and Cirripedia. Density varied seasonally from 1,680 +/- 316 ind/m(3) in October to 29,728 +/- 13,169 ind/m(3) in April, with higher values obtained in the rainy season. Diversity was higher in the dry season, with a maximum value of 2.56 +/- 0.19 bits/id (October). The local zooplankton was affected primarily by seasonal variation in precipitation and associated hydrological variables mainly salinity - which seems to regulate the local zooplankton community dynamics.