Small-scale distribution of the mesozooplankton in a tropical insular system

In the present work, spatial and seasonal fluctuations of the abundance and diversity of mesozooplankton are presented, with special attention being given to copepod assemblages from coastal area of the Fernando de Noronha Archipelago (FNA) (3 degrees 50'24S and 32 degrees 24'48W). Sampling was carried out during the dry and rainy seasons of two consecutive years (July and December 2013) and (June and November 2014). A total of 37 mesozooplankton taxa were recorded, being the copepods the most diversified group (15 taxa). The Subclass Copepoda dominated in both periods sampled, comprising 53% and 86% of the total abundance in the dry and rainy season respectively. The species considered abundant were: Calanopia americana, Undinula vulgaris, Oithona plumifera and Corycaeus speciosus. The rainy season favored a significant increase in the abundance of mesozooplankton and copepods. However, a low value of the ShannonWiener diversity index was observed in this same seasonal period. This was explained by the dominance of the species C. americana and U. vulgaris in the studied area. Spatial differences have not been verified. The copepod assemblages was composed mostly by species considered as predator-carnivours of greater importance on the pelagic trophic web, indicators of oligotrophic conditions and components of a major portion of fish food items. Thus, we suggest that a spatially homogeneous mesozooplankton community characterizes the coastal area of Fernando de Noronha Archipelago with variations related mainly to the seasonal factor.