Meiofauna, a highly diverse group of small metazoans, are ubiquitous in deep-sea soft sediments and exhibit high abundance and biomass compared to larger-sized invertebrates (e.g., macrofauna). The northern Gulf of Mexico deep sea is characterized by topographical contrasts, with the flat topography of the Florida slope followed by the precipitous depth increase of the Florida escarpment; the complex Texas/Louisiana slope with numerous basins and knolls; and numerous canyon features such as the Mississippi Trough and DeSoto Canyon. Meiofauna community structure (abundance, biomass, and diversity) and function (respiration and feeding rates) were analyzed along with environmental variables in a hypothesis-based univariate and multivariate design, to more fully understand the distribution meiofauna, regional species pools, processes structuring communities, and how they respond to topographic, geochemical and physical forcing in the northern Gulf of Mexico.
Meiofauna abundance is significantly related to water depth, but also exhibits significant longitudinal differences resulting from proximity to Mississippi River outflow. Multivariate comparisons of meiofauna abundance and diversity with environmental variables reveals a strong Mississippi River influence. River outflow alters local sediment characteristics, and interacts with loop current eddies and dynamic slope topography to increase POM flux in the northeastern region, thus creating areas of enhanced meiofauna abundance, biomass, and respiration, but lower functional harpacticoid copepod diversity. However, most stations have unique harpacticoid species compositions, suggesting high regional (2700 species) and global (105 - 106 species) diversity by extrapolation. Although highest harpacticoid diversity, in terms of expected number of species (rarefraction), is found at approximately 1200 meters, average taxonomic and average phylogenetic diversity continue to increase with depth, indicating greater morphological or functional diversity. High within versus between station variability suggests an interaction between small and region-scale processes maintaining high diversity. Allometric estimates indicate that meiofauna require 7% of their biomass per day to meet their metabolic energy budget, and account for 10-25% of whole sediment community respiration, indicating their importance in global biogeochemical cycles.