Zooplankton consists of heterotrophic organisms, which play an important role in transferring energy to higher trophic levels. This study aimed to investigate the structure of the zooplankton community at Chapeu Virado beach on the island of Mosqueiro (Belém, Pará), during periods of low rainfall (November and December), and to assess the importance of abiotic factors on possible differences in the recorded ecological parameters. The island of Mosqueiro encompass estuarine beaches, which are dominated by semi-diurnal tides with 3.60 m amplitude, subject to strong hydrodynamics. The samples used came from the collection held by the Laboratory of Aquatic Biology (BIOAQUA/ICB/UFPA). They were taken in four consecutive years (2009 to 2012), through the tidal course of a diel cycle each year. Sampling was carried out through subsurface horizontal tows, with a cylindrical-conical plankton net (150 μm).Sampling occasions and periods were decidedbased on the tides compiled from the tide tables (Directorate of Navigation Hydrography, Brazilian Navy) for the region. Temperature, pH and conductivity/salinity were measuredin situ. Qualitative and quantitative analyzes of the biological material were done under stereoscopic microscopy. The abiotic variables had a stable behavior during the sampling period in each year, but with more accentuated variations between different years, notably conductivity and pH. Thirty-nine taxa were recorded at a specific level, with the vast majority of species belonging to the subphylum Crustacea. Among which, in terms of density, Cirripedia sp. and the families of Copepoda, Acartiidae, Paracalinidae, Pseudodiaptomidae, Oithonidae, Oncaeidae, Tachidiidae, Sergestidae, Bosminidae and Moinidaewere noteworthy. Copepods were the most frequent and dominant in all annual sampling occasions. Short-term temporal differences were observed, with the highest richness at low tides and diurnal ebbs (2009 and 2011). In relation to the differences of medium duration, richness and density were higher in 2009 and 2011. The correlations measured between abiotic parameters and ecological indices were low and not significant. Abiotic factors can affect zooplankton distribution, but their effects were diluted. Low salinities can affect the occurrence of species, determining the dominance of oligohaline species. There is a need to intensify research and better assess the effects of abiotic factors on the zooplankton community both considering medium and long term.
Key words: estuarine beaches; zooplankton; tide fluctuations; abiotic factors.
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