Morphological diversity of tropical demersal fishes across different marine habitats

Fish morphology, a key aspect of phenotype, is influenced by a wide range of environmental interactions involving physical, chemical, and ecological factors. Here, we investigate the morphological pattern of a community of 120 demersal bony fish species in a tropical marine environment (Brazil between 4°-9°S) and examine the relationships between morphology and the different benthic habitat types present in this region. Using geometric morphometric techniques, we established shape groups and evaluated morphology across phylogenetic and taxonomic gradients. We also used the resulting morphospace to understand how morphology correlates with the habitats in which demersal fish species occur. We found 13 major shape groups, demonstrating the high morphological diversity. Body elongation was the main source of morphological variation, followed by caudal fin shape and dorsal fin shape. The morphological clustering showed low congruence with the phylogenetic tree, indicating that our morphological approach is not effective to observe phylogenetic proximities. The more complex benthic habitats, like sand with rocks, coralline formations, and sponges, showed the highest values of diversity and maximum morphological distance. In addition, the greater morphological similarity occurred in the sandy habitat, where we observed the highest abundance of species with elongated body patterns, well adapted to live in open habitats with higher water flow. We recommend that this work be extended to other areas, as morphological understanding is fundamental to gaining insights into ecosystem dynamics, especially in coral reefs.