André Luiz Machado Pessanha

Functional adaptations enable estuarine fishes to exploit habitats along environmental gradients. This study investigated how geomorphological and anthropogenic features of three tropical Brazilian estuaries within semi-arid river basins (Mamanguape, Paraíba, and Gramame) influence the taxonomic, functional, and phylogenetic diversity of fish assemblages during rainy and dry seasons. A total of 11,073 individuals from 118 species and 33 families were recorded. The assemblage was dominated by schooling, zoobenthivorous, fusiform, marine estuarine-dependent, and pelagic traits. We found that: (1) putative seasonality increases taxonomic β-diversity and decreases taxonomic α-diversity, likely due to intensified environmental filtering along estuarine gradients during periods of higher freshwater flow; (2) larger, permanently open estuaries showed β-diversity dominance, whereas the smaller, intermittently closed estuary exhibited α-diversity dominance; and (3) estuaries characterized by smaller mouth widths showed homogenization of species, functions, and lineages, reflecting low functional redundancy and increased vulnerability. Overall, our results show that integrating multiple diversity facets can support stronger connections with conservation priorities for estuarine fish biodiversity, highlighting the value of a multimetric approach in estuaries influenced by a semiarid climate.

For the development of conservation and management strategies, scientists often define a ‘typical’ individual from a population and act as if all members of that group are basically the same, ecologically speaking. However, studies have found that resource use can vary among individuals from the same population, often due to their life stage, and that this variation helps reduce intraspecific competition among them. In this study, the feeding habits and the degree of individual specialization in the use of food resources, determined by the individual specialization index, were analyzed for the populations of the Brazilian silverside (Atherinella brasiliensis), mojarra (Eucinostomus argenteus), and two anchovy species (Anchoa tricolor and Lycengraulis grossidens) in different estuarine habitats. A total of 3855 specimens were collected from vegetated and unvegetated areas during the rainy and dry seasons of 2014. Overall, the highest density and biomass were registered in unvegetated areas. Density differed significantly among sites for A. brasiliensis, while for anchovies it differed significantly among seasons. Species exhibited spatial segregation in feeding, with anchovies feeding primarily in the water column, while A. brasiliensis and E. argenteus were benthic feeders. Despite using similar items, benthic species showed little dietary overlap, coexisting through differential use of prey proportions. A. brasiliensis, E. argenteus and A. tricolor were generalists, with the first two showing high intrapopulational diet variation (low IS values), whereas L. grossidens was a specialist with narrower niche breadth and lower individual specialization. Corroborating the Niche Variation Hypothesis, generalist species had a higher degree of individual specialization, which may be related both to an attempt at resource partitioning and to reducing intraspecific competition.

Intraspecific variations in the morphological traits of juveniles and adults of the Brazilian silverside, Atherinella brasiliensis, from three estuarine habitats were studied to understanding whether their morphology interacts with their dietary composition and habitat structure. For each individual, fourteen morphological measurements and eight functional traits were recorded related to food acquisition and locomotion. The highest abundance of A. brasiliensis was recorded in mudflats, which were often associated with a greater number of juveniles. Overall, 392 A. brasiliensis stomachs were examined, and their diet comprised mainly zooplankton organisms, followed by insects and benthic crustaceans. Among the morphological measures, our data revealed that in vegetated habitats (seagrass and riparian vegetation), individuals showed a higher oral gape surface and caudal peduncle and fed predominately on epibiotic or benthic fauna, while for individuals that had bigger eyes in unvegetated habitats (mudflat), this facilitated the ingestion of zooplankton and diatoms. Furthermore, a greater relative body height recorded in unvegetated habitats enhanced swimming performance and was linked to the effects of the lowest habitat structure. The results highlight the significant effects of morphological variation on juvenile and adult food acquisition and swimming ability.

Pneumatophore fringes and mudflats are extremely valuable habitats and provide structures on which many fish species benefit in terms of food and reduced predation risk. We analyzed the spatiotemporal patterns in feeding habits, reproductive aspects and effects of predatory fish presence to assess the ecological drivers of the common halfbeak, Hyporhamphus unifasciatus, in a Brazilian estuary. Sampling was conducted during the rainy and dry periods. In summary, the results demonstrated that the number of predatory fishes was a strong predictor of population abundance and biomass, followed by pneumatophore complexity. The abundance and biomass values tended to increase with increasing habitat structural complexity towards the upper estuary. There was evidence that fish exhibited movement during the rainy season related to spawning events and subsequent juvenile recruitment in this area. Hymnoptera was the item most frequently ingested and made the greatest contributions to the volume of diet in habitat types throughout the year. There was an increase in the condition factor in the rainy season, which was associated with energy reserves, reproduction and growth (fitness). We concluded that predation is an important ecological process that operates at local spatial scales and that, together with the density of pneumatophores, it could affect the abundance of common halfbeak populations associated with estuarine habitats.