Variation in species diversity within macrobenthic invertebrate communities in the western Gulf of Mexico

Abstract

Species diversity, richness, and evenness have been compared in the macrobenthos along an environmental gradient from the Galveston Bay estuary to the abyssal plain of the western Gulf of Mexico. A parabolic pattern in diversity was found, with minimum values in the estuary, maximum on the continental shelf (~100-500 m), and low values on the continental slope and abyssal plain. The maximum diversity was found at a much shallower depth (-100-500 m) in the Gulf of Mexico when compared to other basins where similar estimates have been made. The regulating mechanisms within the estuary controlling diversity were hypothesized to be salinity and temperature, two highly variable parameters. As expected from the literature on similar mesohaline estuaries, diversity decreased with increased salinity variation. The high diversity found on the continental shelf was attributed to mild or benign physical fluctuations and predation, consistent with the "dynamic equilibrium model'' (Dayton and Hessler 1972). Diversity decreased from the continental shelf to the continental slope and abyssal plain. Possible causes of this pattern are hypothesized to be the basin's: 1) young age, 2) elevated temperature (+4C̊) compared to similar depths in the Atlantic, 3) limiting still depth (~1600 m), and 4) intermittent turbidity currents or slumps coming off of the Mississippi Canyon.