Modelagem ecossistêmica e simulações de esforço de pesca em um estuário hipersalino da região semiárida do Brasil

Abstract

The modeling of trophic networks is a widely used tool in understanding the interactions between organisms and the processes that occur in the ecosystem. Through a trophic model it is possible to evaluate the energetic flow between species, to describe the function they perform and to evaluate the maturity of the ecosystem. Such applications can provide relevant conservation and management subsidies. Among the different modeling concepts, Ecopath has stood out for its application in aquatic ecosystems. The objective of this study was to elaborate an Ecopath model of a shallow estuary and low river flow (Pacoti River, northeastern Brazil). From this, we aim to analyze the ecosystemic attributes that describe the structure of the trophic network and to simulate an increase of the fishing pressure in the system. The information needed to elaborate the model was obtained through a bibliographical survey and ichthyofauna samples collected by the Laboratory of Aquatic Ecology and Conservation of the Federal University of Ceará between the years 2014 and 2015. In addition, field research was carried out throughout 2018 for identification of birds. The model presented a total of 30 compartments, from primary producers to top predators and one of drebris. The average trophic level of the community was 2.06. Most of the biomass was concentrated in the second trophic level, mainly by the contribution of the compartments of the benthic macrofauna, composed mainly of Poliquetas and Bivalves. Most of the flows in the trophic network of the estuary are supported by Detritus, indicating the importance of this compartment to the system and also its difference from typical tropical environments. The compartments with the highest value of the key species index were: Piscívoros and Centropomus parallelus, with trophic level of 3.43 and 3.31, respectively. The genus Diapterus appears in third place as a key species and represents an important link between the lower and higher trophic levels. The ecosystem attributes calculated by the model reflect a developing system. Most of the development capacity is due to Overhead (55.96%), indicating a high amount of disordered information and thus good system resilience. The simulated increase in fishing pressure mainly affected Diapterus spp. and Lutjanidae, in addition to a trend of increased biomass of macroinvertebrates and birds. The increase in simulated fishing pressure resulted in wide changes in the community, especially in the fishery, with a decrease in its total biomass. This study contributes to the knowledge about trophic webs in shallow and low flow estuaries, both in terms of their basic attributes and also the possible trends caused by fishing pressure. The simulated effects evidence the role that species typically fished in estuaries of the region have in the community structure.