Ecological aspects of mesozooplankton in marine protected area of the tropical southwestern atlantic

Abstract

The zooplankton biomass (BZ), copepod assemblages structure, abundance, biovolume and size of mesozooplankton are important ecological descriptors in the management and conservation of marine resources. In the present study, the spatial, interannual, sampling time and transect positions effect were tested on these descriptors. The results were based on 96 samples of zooplankton collected in three years (July/2010, September/2012 and August/2014) in the surroundings of the Fernando de Noronha Archipelago (FNA), Rocas Atoll (RA) and St. Peter and St. Paul (SPSPA). The ZB (mg.m-3) varied significantly in space, where SPSPA had a significantly higher average value compared to FNA and RA. The effect of the sampling time also influenced the ZB, where the nighttime average was higher than the daytime. The year 2010 registered the lowest significant value of ZB, where we suggest that it could be a serious repercussion associated with the high temperature of the sea surface registered in several parts of the world and especially in the Tropical Atlantic Ocean. The hypothesis of spatial heterogeneity was demonstrated, showing that the SPSPA has the highest copepods abundance (ind.m-3) and the lowest species richness when compared to the other island systems studied. The significant increase in copepods abundance downstream was suggested as a consequence of the "Island Mass Effect". Samples were analyzed using the ZooScan system. A total of five size classes were established: 0.3 to 1 mm; 1 to 2 mm; 2 to 3 mm; 3 to 4 mm; 4 to 5 mm and > 5 mm. The results show the abundance and biovolume (mm.m-3) response of mesozooplankton to the spatial effect, whose average values were elevated in the remote SPSPA. We also highlight that the fraction (0.3 to 1 mm) dominated in the SPSPA, indicating that this is the biologically most productive island. The lowest values of abundance and biovolume of mesozooplankton were verified in July / 2010. The high contribution of organisms with higher body volume at night was explained by the high abundance of size classes: 1 to 2 mm; 4 to 5 mm and > 5 mm, which corresponds to the size of organisms considered to be strong migrators. Furthermore, it is important to consider that the smaller fraction (0.3 to 1 mm) did not respond to the effect of sampling time, nor in relation to abundance neither biovolume, which can be explained by the predation or absence of vertical migration.