Taynara Pontes Franco

The inshore area of the Southwestern Atlantic between 22 °S and 29 °S (South Brazilian Bight) is a transitional climatic zone, where the tropical and warm temperate provinces mix. In its northern part, i.e., in the coastal waters of Rio de Janeiro, Brazil, local oceanographic conditions, such as upwelling in the north, and great bays with different degrees of anthropogenic influences in the center and south can determine the population structure of several fish stocks. The Whitemouth croaker (Micropogonias furnieri) is one the most heavily exploited fishing resources in this area, but there are still some doubts about its population structure. In this study, through combined analyses using nuclear genetic markers and morphological and geochemical signatures of otoliths, a divergence of individuals between two populations was identified using microsatellites, while a finer spatial structure with three populations (north, center and south, respectively) was found based on otolith shapes and elemental signatures. This regional population structure may have direct implications for rational fisheries management and conservation of the species.

In the late 1970s, studies on the population structure of S. brasiliensis suggested the existence of two stocks, considering distinct regional somatic growth rates and spawning areas (23–25° S and 26–28° S). This scenario was further confirmed by geochemical signatures of whole otoliths combined with basic biological data regarding 2-year-old sardines collected in SW-S Brazil. However, information about sardine movements and connectivity between their main juvenile recruitment areas and the adult fishing grounds is currently limited. In this study, natal otolith elemental fingerprints (core section) of young-of-year (age 0+) and adult (age 2+) individuals were collected, respectively, in the main spawning areas (2019) and fishing grounds (2021) and evaluated. Elemental signatures of recruits were compared with those of adult fish from the same cohort to estimate connectivity between juvenile recruitment areas (RJ-22° S, SP-23° S and SC-26° S) and regional adult populations captured in the major fishing grounds (22–23° S, 24–25° S and 26–27° S). Uni- and multi-elemental chemical signatures showed significant differences for age 0+ and for age 2+. Pairwise comparisons associated age 0+ and age 2+ with the northern distribution area (RJ + SP) and differentiated them from those of SC. The leave-one-out reclassification matrix combining chemical fingerprints and reassigned the individuals to their original areas with moderate-to-high accuracy: RJ 0+ (85%), SP 0+ (80%), SC 0+ (85%), and from RJ 2+ (80%), SP 2+ (70%), SC 2+ (75%). This variability was driven by Ba/Ca, Fe/Ca, Mg/Ca, Mn/Ca, and Sr/Ca ratios. Maximum likelihood analysis suggested for the 2019 cohort that replenishment of adult populations of S. brasiliensis along the Brazilian coast was mostly derived from the northern recruitment area (RJ + SP = 64%). Nonetheless, an important contribution from the southern counterparts to the northern stock was detected (36%), supporting the hypothesis of meta-population structure.

Changes in coastal environments are usually caused by anthropogenic activities such as habitat degradation and nonpoint source pollution. Such changes reduce the life quality of the living organisms in altered environments, decreasing biotic descriptors and jeopardizing biodiversity. The aim of this study was to compare eventual changes in minor and trace elements in otoliths of the catfish Genidens genidens in two periods (1980s and 2017–2018) in an altered tropical bay (Sepetiba Bay, RJ, Brazil). The concentrations of 34 elements were determined by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) in fish otoliths. Although some elements have shown higher concentrations in more contemporary periods (2017–2018) such as ⁷Li, ¹¹Br, ⁸⁵Rb, and ²⁰⁵Tl, and some did not differ between the two periods (²⁰⁸Pb, ³⁴S, ⁴⁴Ca, ⁵⁵Mn, ⁸²Se, and ¹³⁷Ba), but most of the examined elements (such as ²⁴Mg, ⁵⁹Co, ⁶⁰Ni, ⁶⁵Cu, ¹⁰⁵Pd, ¹⁰⁷Ag, ⁶⁶Zn, ⁷⁵As, ⁶⁹Ga, ⁹⁸Mo, ⁵³Cr, ²⁷Al, ¹¹⁴Cd, and ¹¹B) had higher concentrations in the 1980s compared to 2017-2018 (test w, p < 0.05). Although this result was the opposite of what was expected, this could be associated with the intensity of activities without any environmental control in the past and with the first dredging to deepen the access channel to the port created in 1982, allowing the operation of large ships, which promoted the resuspension of trace elements trapped in the sediment and the pollution carried into the bay. The stability of the incorporation of elements in otoliths, compared to other tissues, allows such records, which are consistent over time, to be used in order to better understand past and present variations in the quality of the environment. Such information can be useful in conservation programs as it provides a historical view of variations in the quality of the environment.

Disentangling multilevel sources of variation is critical for understanding of diversity patterns in high-variability environments. We investigated the scale sensitivity of short-term environmental effects on the temporal beta diversity of fishes in 3 tropical coastal lagoons in Southeastern Brazil. Environmental effects were investigated at 3 hierarchical levels (local, zone, and lagoon). An AICc-based model selection was applied to generalized linear mixed models relating abundance-based beta diversity (Bray-Curtis dissimilarity; β_BC) to environmental distances and random effects for other sources of variability. Abundance gradients (β_BC-GRA) contributed more for β_BC at all hierarchical levels, most likely due to random changes in the abundances of numerous rare marine-origin species. The temporal and spatial marine influences favored the balanced variation in the abundance of different species (β_BC-BAL), probably by allowing for marine species with different environmental tolerances and requirements. The freshwater vs. marine influences were primarily represented by short-term effects of salinity changes at the local and zone levels and tide height and accumulated rainfall at the lagoon level. Other environmental effects (e.g. pH and transparency) were representative of that balance depending on the β_BC component and hierarchical level. Random effects for morphometric features (local level, width of the connections between zones; lagoon level, distance from the ocean) and climate-related factors (local and zone levels, wind intensity and accumulated rainfall; lagoon level, changing seasons) were also relevant for the relationships between environmental variability and β_BC. This study evidenced major scale-related mechanisms driving the temporal beta diversity of fishes in tropical coastal lagoons.