The Assemblage Structure and Trophic Ecology of a Deep-Pelagic Fish Family (Platytroctidae) in the Gulf of Mexico

Members of the family Platytroctidae (tubeshoulders) are found throughout the meso- and bathypelagic waters of the World Ocean. Due to the lack of specimens collected globally, this taxon has received little attention, despite recent evidence suggesting its predominance in the bathypelagic biome. Prior to this study, only four species had been reported in the Gulf of Mexico’s (GoM) highly diverse deep-pelagic ecosystem. An extensive meso- and bathypelagic trawl series in the GoM allowed a detailed examination of this family, which included analyses of species composition, abundance, vertical distribution, sex ratios, and trophic ecology. A total of 16 species were collected, which included 12 new records for the GoM. The five most-abundant species collected were Mentodus facilis, Platytroctes apus, Barbantus curvifrons, Mentodus mesalirus, and Maulisia microlepis. All platytroctids were collected from tows that extended below 700 m. Mentodus facilis was the only species that significantly differed from the expected 1:1 sex ratio (pMentodus mesalirus and Maulisia microlepis heavily consumed gelatinous zooplankton. Mentodus facilis and Barbantus curvifrons had a more varied diet consuming chaetognaths, copepods, and ostracods, with M. facilis exhibiting a slightly greater reliance on ostracods and gelatinous prey. This study represents the first investigation into the diet of this fish family and adds to the sparse community data of the bathypelagic zone by identifying alternative nutrient pathways (e.g., the fish-jelly link) that connect the deep and upper oceanic ecosystems.