Fish diversity, composition, and guild structure influenced by the environmental drivers in a small temporarily closed tropical estuary from the western coast of India

Physicochemical variables influencing the abundance of Atlantic goliath grouper juveniles (Epinephelus itajara) in a tropical Brazilian mangrove habitat

The purpose of this study was to investigate the relationships between the abundance and occurrence of juvenile Atlantic goliath grouper and physicochemical variables in a tropical mangrove ecosystem, employing a non-lethal methodology. Juvenile Atlantic goliath grouper individuals were captured biweekly, using blue crab traps, across three locations within the São Mateus estuary (18°36'S, 39°44'W), from August 2021 to July 2022. Simultaneously, the physicochemical water variables were assessed during each trap inspection. The physicochemical water variables influence on the abundance and occurrence of Atlantic goliath grouper juveniles were assessed using the Zero-Inflated Binomial (ZIB) and the Poisson (ZIP) generalized linear mixed-effects models (GLMMs). A total of 66 Atlantic goliath grouper juveniles were sampled (Pontal do Sul = 50, Lagoa Creek = 13, and Pitangueiras Creek = 3), ranging from 32 to 319 mm in total length. The best model fitted to presence-absence data (AIC = 278.6) consisted of location, depth, and salinity, with only location having a significant influence on the likelihood of species occurrence. Regarding abundance data, the best model (AIC = 336.4) included location, depth, and turbidity, with only location and depth showing a significant impact on abundance variation, with lower abundance at deeper areas. Although our results indicate a weak significant influence of physicochemical variables on juvenile Atlantic goliath grouper distribution, it is imperative to continue this monitoring effort, considering that additional data may be required to gain a deeper understanding of these patterns.

Fish community structure and functional guild composition in an anthropogenically impacted, temporarily closed sandbar estuary

This study investigates the fish assemblage in a temporarily-closed sandbar estuary along India's west coast, across different zones and seasons. Moderate species diversity (54 species), low species abundance, varying fish diversity from lower to upper estuarine gradient (higher counts in lower zones, and decreasing from middle to upper zones), and higher prevalence of marine migrants (estuarine use) and piscivorous species (feeding mode) were the significant characteristics of the estuary. Distinct spatial, seasonal, and estuarine mouth state-based variations were recorded in the estuary, based on diversity indices and count of taxa. Peak diversity and abundance were noted during the pre-monsoon, and during the open mouth state of the estuary. The entire estuarine gradient is anthropogenically impacted by a multitude of stressors, except at the estuarine mouth region, which is favored by marine connectivity. The fish assemblage structure in Poonthura estuary (PE) has thus far remained unaffected by anthropogenic disturbances. Nevertheless, growth and nursery function of the estuary have been significantly compromised. The predominance of juvenile fish in the ecosystem, and prevailing anthropogenic stressors from point and non-point sources underscore the necessity for long-term maintenance of the population of coastal species, as well as a need for developing and implementing urgent management strategies for this fragile ecosystem.