Ecologia do mesozooplâncton de um estuário semiárido tropical

Abstract

Estuary is a semi-closed coastal region, whose main characteristics are the constant mixing of fresh and salt water and the dominance of fine sediment that forms the mud banks. Among the organisms that inhabit this environment, there is zooplankton, a vital part of the food web of coastal and ocean waters, and the link between primary producers and secondary consumers. The present study aimed to study the mesozooplankton community in the estuary of the semiarid River Pacoti (Brazil, Ceará), highlighting the ecological, production and copepods bioindicators. Zooplankton was collected in spring tides (ebb, low, high and flood tides), during rainy (March, April and May 2008) and dry seasons (September, October and November 2008). Sampling was carried out at a distance of approximately 3 km from the mouth of the estuary Pacoti through subsurface horizontal hauls (300 µm), coupled with General Oceanics flowmeter, samples were immediately fixed on board with 4% formalin, buffered tetraborate Sodium (5 gL-1). In the estuary Pacoti, the mesozooplankton proved resilient. However, we cannot say that this condition is commonly found in semi-arid conditions, because few studies have been conducted under this approach. The production of copepods studied, considering the different tides, showed no patterns or trends. The existing variations are due to the influence of abiotic parameters that influence the occurrence of the species in the estuary. Despite the occurrence of several species habitats, we can infer that the region where the study was conducted, about 3 km from the mouth, there is a strong marine influence, because there were a few species of limnetic and low densities, even during the rains. Thus, the zooplankton community Pacoti River estuary can be defined as marine euryhaline. Mesozooplankton bioindicators showed efficiency with the origin of the water masses: freshwater, estuarine or marine. Signs of eutrophication can be verified across species Acartia lilljeborgii, Euterpina acutifrons, Oithona spp., Oithona oswaldocruzi and Oikopleura dioica.