Aspectos do ciclo de vida de lutjanídeos em ambientes estuarinos tropicais: uso do habitat e padrão de movimento

Abstract

The Lutjanidae family is represented by fish of ecological and economic importance in coastal environments (snappers) that use these areas as nurseries. Knowing the patterns of use and sharing of these areas is fundamental for the management and conservation of priority areas. Chemical analysis of otoliths has been used for studies on fish, including shifting and habitat use. The objectives of the present study were to use this tool to verify spatial variations in the chemical composition of Lutjanus synagris otoliths in estuarine regions of Bahia and, through the chemical reading of the Sr and Ba deposition pattern of the edge of the L. jocu otoliths, L. analis and L. synagris, to discriminate the use of the habitat by the lutjanids. The study was carried out in Baía de Todos os Santos (BTS), Baía de Camamu (CAM) and Caravelas Estuarine Complex (CAR). Seven expeditions were carried out in each region between July/2015 and September/2017. The fish were dissected and their otoliths removed, processed and sent for analysis. In the laboratory the analyzes of the edges of the L. synagris otoliths were carried out by means of a laser ablation system coupled to a plasma induction mass spectrometer. Subsequently, the chemical analysis of the isotope deposition pattern of Sr and Ba of the edge of the otoliths of L. jocu, L. analis and L. synagris of the three regions was used. In order to verify habitat overlap, the Ba and Sr ratio concentration averages were compared between the species in each locality, using Mann-Whitney test for BTS, and Kruskal-Wallis for CAM and CAR. Altogether, 29 juveniles of L. synagris were caught in the estuaries while 41 adults were caught outside the estuaries. In addition, 220 otoliths were analyzed, 61 of L. analis, 126 of L. jocu and 33 of L. synagris. Significant differences were found in the composition of the L. synagris otoliths between estuarine and marine regions for Ba, Sr and Mg in the three regions showing that the same species shows different chemical signatures. In CAM there were higher values for Ba and Mn, and lower values of Sr, indicating a higher fresh water intake in this region. BTS was always intermediate in the values of Ba, Sr and Mn, indicating a moderate mixture of fresh and salt water in comparison to the other areas. In CAR, which does not have a bay formation, the values of Sr were the highest, while those of Ba were the lowest, possibly due to the greater influence of the marine environment. The otoliths of the three snappers did not show significant differences between the areas except for the SR in CAR. This result shows that there is spatial overlap for all species studied. It is not possible to affirm with this that there is niche overlap, and the literature shows that the diet with preferentially different food items may be a factor that allows the coexistence of these species. However, more work is required to better investigate this hypothesis in the areas studied.