Implications of the depth profile on the functional structure of the fish community of the Perdido Fold Belt, Northwestern Gulf of Mexico

Studies have demonstrated that environmental conditions affect the richness, diversity, and abundance of fish communities. Depth is an important variable with many species showing preferences for specific depth ranges. Here, we present a functional analysis of the fish community in the Perdido Fold Belt (PFB), Gulf of Mexico. The sampling design was structured across a depth range of 40-3500 m, using 20 oceanographic stations. The aims of our study were: (1) to determine the functional arrangement of the fish community in the PFB; and (2) to describe the effect of the environmental variables on fish richness and functional diversity. A total of 232 species were identified; 195 were grouped into 42 functional groups (FGs). Thirty-seven species did not group with any others and are referred to as "functionally independent species" (FIS). According to our results, depth changes in physicochemical variables allow us to segregate three vertically stratified zones: shelf, slope, and deep. Temperature was the most important environmental variable constraining functional distribution of fishes. The highest FG diversity, species diversity, and biomass were found in the shelf/slope zone (SSo), while the highest diversity of FIS was found in the shelf zone. As the SSo displays its highest diversity, and since greater diversity has been linked with greater resilience and stability of fish communities, the SSo may be the most resilient zone of the PFB. Our study provides the first description of the diversity and resilience of the PFB fish community and helps our understanding of the factors constraining the distribution and functional diversity of fishes across depth gradients.