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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. [ABSTRACT FROM AUTHOR]

Shallow estuarine habitats are well recognized for providing a positive correlation to the abundance and diversity of juvenile fish species. This has been associated with the hypotheses of refuge from predators and the availability of food. Therefore, this study aimed to evaluate the importance of two adjacent habitats to mangrove fringes (area adjacent to pneumatophore zone and mudflat) as an ecological habitat for Diapterus auratus juveniles. Sampling was carried out in the rainy (January–July 2016) and dry (August–December 2016) periods. This study indicated that D. auratus juveniles did not show significant differences in abundance and biomass between adjacent habitats. However, univariate analyses found there was a significant increase in fish abundance in the dry season, due to influx of young-of-the-year. Further, the size-frequency of D. auratus showed a recruitment pattern recorded between August and January, suggesting a broad spawning period between the end of the rainy season and a recovery period between March and May. There were distinct changes in the diet between seasons for D. auratus, according to the dendrogram of the food eaten by the fish. The combined results from the distribution and feeding ecology suggest a connectivity among adjacent areas, and indicate that both habitats provide critical foraging and refuge habitat for D. auratus in this tropical estuary. [ABSTRACT FROM AUTHOR]