Fatores determinantes para a diversidade de zooplâncton em tanques de pedra na região semiárida brasileira

Abstract

Freshwater rock pools include all types of depressions that occur in rocky substrates that hold freshwater. They are found all over the world in all major biomes and are known by different names, have varying degrees of isolation and connectivity, and are mostly temporary habitats that occur in semi-arid or temperate regions. Thus, the hydroperiod and its hydroregime are the main structuring factors in temporary waters. Among the communities of temporary ecosystems, phytoplankton is the collective of photosynthetic microorganisms, which have a close relationship with the environmental characteristics and the geographic location of the pools. In addition, zooplankton feeding activity exerts a great influence on phytoplankton proliferation. Zooplankton is a group that is sensitive to environmental changes and plays an important role in the food chain, transferring mass and energy from primary producers to higher trophic levels. It was hypothesized that the spatial structure of the zooplankton community is closely related to the availability of palatable algae. Thus, the aim was to analyze the effect of biotic and abiotic factors on the diversity of zooplankton present in rock pools in the Brazilian semiarid region. Twelve rock pools located in Casserengue - PB were selected, where samples of water, phytoplankton and zooplankton were carried out during the month of March 2019. Phytoplankton were classified according to their palatability, based on their size, and according to their functional groups. For zooplankton, density and frequency calculations were performed. Overall, rock pools showed varying levels of isolation, shallow characteristics, high temperatures and alkaline pH. For biological communities, 12 phytoplankton species belonging to 4 Classes were identified. Regarding palatability, all observed phytoplankton taxonomic groups are within the established range. In addition, the presence of zooplankton from the Copepoda, Ostracoda, Cladocera and Rotifera groups was observed, with higher densities of Ostracodas and lower densities of Cladocera. The frequency of occurrence was constant in the Class of ostracods, while most of the other taxa presented accidental occurrence along the studied points. Therefore, the results show that the pools that have connections showed similar taxonomic groups of zooplankton, while more isolated pools in the landscape showed a greater diversity of zooplankton groups, probably due to the difference in local characteristics, such as conductivity, depth, STD and temperature. We identified a higher density of zooplankton associated with higher phytoplankton biomass indicating a potential for herbivory pressure in these pools.