Biological traits and functional diversity of free-living nematode assemblages along a water-depth gradient in the northwestern of Gulf of Mexico

This study analyzed the biological traits (BTs) and functional diversity (FD) of free-living nematodes in the northwestern of Gulf of Mexico. We collected sediment samples at 27 sites at a depth gradient from 44 to 3466 m. The nematodes were identified at species level and classified in five groups of BTs: feeding type, amphid shape, tail shape, body shape, and body length. We determined the FD based on the combination of BTs through a functional dendrogram, using the total length of the branch as a measure of functional diversity. Salinity, pH, and dissolved oxygen were measured in each site, as well as the sediment composition and percentage of organic carbon (OC). A total of 1673 nematodes were identified, belonging to 35 families, 96 genera, and 153 species. The number of species varied along water depth (1–60 species). The more abundant BTs were the non-selective deposit feeders (49 %), amphid spiral shape (55 %), clavate conical cylindrical tail (52 %), sizes 1000–1500 μm (51 %), and body shape slender (97 %). The most common combination of traits was non-selective deposit feeders, spiral amphid, clavate conical cylindrical tail, slender shape, and sizes < 1500 μm. The changes of BTs with increasing depth were more evident in the feeding types and amphid shape. The FD fluctuated between sites (0.42–0.99) and was significantly correlated with the number of species, suggesting that taxonomic and functional diversity have similar responses to environmental variables. The FD was significantly influenced only by the percentage of sands. Our data provide valuable information that can be used in subsequent studies and benthos monitoring.