Mangroves are important habitats for fish across latitudinal gradients, but few studies have examined fish community functional diversity in mangroves from arid environments. To address this, we assembled 11 morpho-functional traits and taxonomic diversity for 123 fish species and environmental characteristics from 3 mangrove ecosystems in the Gulf of California, where arid conditions prevail. We compared these arid mangrove fish communities to a semitropical community in an estuarine condition to analyze functionality. Arid mangrove fish communities were similar to each other, but different from semitropical estuarine fish communities (R = 0.951, P = 0.007). Mangrove fish communities had higher trait diversity than the estuarine community, but the estuary had higher redundancy. Taxonomic diversity showed a latitudinal gradient, with the southernmost site in the arid region functioning as a transition site to estuarine communities. Despite the different taxonomic composition, the functional structure remained similar in the fish communities within the arid region and had higher counts of diverse traits than the site with estuarine conditions. High salinity and evaporation deficit in the arid mangroves relaxed habitat filtering pressures relative to the estuarine conditions, where the higher tolerance to salinity changes imposes redundant morphologies. Future studies should focus on seasonal variation of environmental effects on the functional aspects of the fish community.

Studying fish communities in extreme habitats is important to better understand the variation in their ranges under climatic scenarios or anthropogenic pressure. In particular, the mangroves in Baja California Sur occupy the northernmost distribution range under two extreme conditions (temperate waters and arid weather). In this context, the aim of the presently reported study was to analyze the functional characteristics of ichthyofauna in two localities, La Paz Bay (BP) and Almejas Bay (BA), which are also located in different ecoregions. For both bays, the composition and frequency values were compiled from monthly samples and the literature. Eleven functional traits were assessed from the morphology of every fish species. Functional indices (Richness, Evenness, Divergence, and Originality) were used to evaluate different aspects of the community structure. A total of 83 species were found at both sites, with 54 in BP and 50 in BA. In BP, six species were residents, eight were temporal visitors, and 36 were occasional visitors. In BA, six species were residents, 15 species were temporal visitors, and 33 were occasional visitors. At both sites, 12% of the species were permanent residents; BA had a higher percentage of temporal residents (27%), while BP had a higher percentage of occasional visitors (72%). The functional analysis detected communities with specialized traits, but in comparison to BP, BA had higher evenness in the community structure. Although greater structural complexity was expected in the community during the warm months, because of the increase in richness and attributes, BA had higher values during the cold months, which was probably because the area is a transition zone and the fish communities are adapted to colder climates. In comparison to BA, BP had higher originality values, and colder months presented higher values than warmer months. Although the mangrove sites had the same northernmost latitudinal limits and both had extreme conditions compared to those in mangroves in tropical environments, the fish communities differed in their composition, frequency, and functionality with more extreme functional traits in colder weather than in warmer weather.

The Parque Nacional Sistema Arrecifal Veracruzano (hereafter called PNSAV) is the largest coral reef extension in the central region of the Gulf of Mexico. These reefs are unique since they have developed near a coastal environment that is directly influenced by the discharges of Veracruz city, the rivers located on the continental shelf, and the port of Veracruz. This study evaluates the functional diversity, in terms of richness, evenness, and divergence, of the PNSAV fish community. We were interested in quantifying any similarities or differences in functional diversity metrics when one examines reef fish assemblages on a single reef or joint reef subsystems; thus, is there a difference based on scale? A total of 297 fish assemblages were observed in seven PNSAV reefs between May 2006 and April 2021. Significant differences were found in the Functional Richness of the assemblages between subsystems, years, and reef-depth interaction, but none were found among the reefs, or between seascapes. The Functional Diversity presented annual mean values between 0.83 (sd= 0.085) and 0.90 (sd= 0.068) and did not show statistical differences between years, seascape, or reefs. In contrast, statistical differences were found between subsystems, and depth level and the seascape-depth interaction. The annual mean Functional Evenness values ranged between 0.34 (sd= 0.128) and 0.44 (sd= 0.060), and significant differences were detected between years, reef, and reefs-depth level interaction, but no difference were found between subsystems. Reef-fish diversity was greater within the north coral reef subsystem than the southern of the PNSAV. There were no overall tendencies for increased functional diversity throughout the time during this study.