Spatial, diel, and seasonal changes in the fish community structure of a Mexican tropical estuary

To extend our knowledge about spatial and temporal variations in the structure of estuarine fish communities, diel samplings (collections every 2 h) were carried out every two months over a one-year period in two different habitats (vegetated and nonvegetated). We collected a total of 34,766 individuals, corresponding to 72 species, most of them with marine and tropical affinities. Species richness was significantly higher in the vegetated habitat, whereas abundance (number of fish) was higher in the nonvegetated habitat. The diel pattern of abundance showed peaks at dusk and dawn, whereas richness was higher at night. Seasonally, fish abundance and species richness showed peaks during January, March, and July–September, and these peaks were related to the entry of temperate species, production processes in the system, and rainfall pattern. Fish assemblages showed significant differences among habitats, day/night, and months. In the vegetated habitat, Lagodon rhomboides, Menidia beryllina, and Orthopristis chrysoptera were the predominant species. Microphagus species such as Brevoortia gunteri, Brevoortia patronus, and Mugil curema were predominant during the warm, dry season (March–May) and they were more abundant during the day. In contrast, predatory species such as Citharichthys spilopterus and Opsanus beta were more abundant during the rainy season and their capture was higher at night. The two most numerically abundant species, Anchoa mitchilli and Membras martinica, showed a twilight pattern, with abundance peaks at dusk and dawn, respectively. Hence, in Pueblo Viejo Lagoon (Mexico), the spatiotemporal changes in species composition are in part related to predator avoidance and feeding strategies, through a coupling of life histories with the diel and seasonal variation in the availability of resources, the presence of submerged vegetation playing an important role in this dynamic

Cross-Shore, Seasonal, and Depth-Related Structure of Ichthyoplankton Assemblages in Coastal Alabama

Investigations of the spatial and temporal structure of larval fish assemblages are essential for a better understanding of the dynamics of fish populations and their resilience to environmental change. This study provides an original typology of the spatial, seasonal, and depth-related structure of ichthyoplankton assemblages collected along a 77-km cross-shore gradient in Alabama coastal waters. This typology is based on a depth-discrete ichthyoplankton survey conducted across multiple years at a high spatial and temporal resolution in the northern Gulf of Mexico. A total of 350,766 larvae were collected, among which \u3e95% could be identified to families. The total density of fish larvae was significantly higher inshore, whereas the number of families increased offshore. Multivariate regression trees and Dufrêne–Legendre indices were used to identify seven assemblages dominated by different families of larvae. These assemblages were primarily structured by distance from the shore, followed by season and depth, and were associated with different water masses characterized by distinct temperature and salinity conditions. Families Clupeidae, Bregmacerotidae, Synodontidae, Scombridae, and Ophidiidae were typical offshore, whereas families Engraulidae, Gobiidae, and Gobiesocidae were typical inshore. These observed spatial distributions likely reflected interactions between adult spawning behaviors and oceanographic processes, in particular the influence of the Mobile River. Our results thus confirm existing lines of evidence suggesting that riverine influences play a major role in fish population dynamics along the Alabama inner shelf. For many families, the observed seasonal distributions were largely consistent with the results of previous studies conducted at smaller spatial resolution in the area. However, our large-scale, high-resolution, cross-shore design clearly improved the detection of seasonal variations for inshore and offshore taxa otherwise rarely collected