Plâncton e microplásticos flutuantes dos recifes de Serrambi (Ipojuca, PE), durante um ciclo circadiano

Abstract

Reef plankton is of vital importance to marine ecosystems as it represents the basis of the pelagic food web in the oceans, and changes in its composition and structure can cause profound changes at all trophic levels. This study aimed to understand the dynamics of the plankton community and the floating microplásticos of the Serrambi beach reefs located in Ipojuca, south coast of Pernambuco, and whether there is influence of a circadian cycle on the structure of these important plots of the pelagic system. The sampling campaign was carried out during a complete circadian cycle in a rainy season, corresponding to the following moments: (i) daytime ebb tide; (ii) nocturnal ebb tide; (iii) daytime flood tide; and (iv) night flood tide. Samples were collected from horizontal trawls and near the reefs, using plankton nets of 20 μm (phytoplankton) and 65 μm (zooplankton). For the microplastics, the samples of this last plot were considered. The phytoplankton groups observed were cyanobacteria, diatoms and dinoflagellates. The values of the phytoplankton density were very different in the four collection times, varying between 123.82 and 1783.02 cells / L, with numerical predominance of diatoms (93.5%). As for zooplankton, the variation in the occurrence of the zooplankton groups was relatively low on all four occasions; however, the density found was very high during daytime (38943.4 ind. m-3) and nocturnal (38460.4 ind. . m-3), with emphasis on copepods (65.92%). Considering microplastics, (i) yarns and lint were found, (ii) hard fragments and (iii) soft fragments of microplastics, all of secondary origin of different colors and sizes, demonstrating several possible sources. The values of the microplastic densities during the circadian cycle are very similar, ranging from 5.19 microns. m-3 (night flood) and 17.69 microns. m-3 (nocturnal ebb), demonstrating also to respond to tidal variation. These results demonstrate how tidal variations occurring along a circadian cycle may have a strong influence on the structure and dynamics of plankton and microplastics. In addition, it is possible to infer that the main environmental variable along the circadian cycle to act on these elements is the tidal variation, with potential influence on the upper trophic links and dependent on seston particles.