Patterns in phytoplankton and benthic production on the shallow continental shelf in the northeastern Gulf of Mexico

Abstract

Shallow continental shelves support productive pelagic and benthic communities. This study examined primary productivity at a shallow shelf region in the northeastern Gulf of Mexico focusing on the effect of light on water column and benthic productivity at water depths between 12 and 17 m. Measurements were made between November 2015 and September 2016. Dissolved oxygen fluxes were measured using benthic chambers with four different light levels and used to calculate gross primary production and respiration. Phytoplankton productivity was measured using 14C-uptake incubations in a laboratory photosynthetron. Organic matter production by benthic microalgae is substantial in this region of northeastern Gulf of Mexico with daily production rates ranging from 0.1 to 0.8 g C m−2 d−1 in this study. Maximum rates of phytoplankton production up to 2.7 g C m−2 d−1 occurred in spring. This peak productivity followed wind conditions favorable to upwelling and occurred when bottom water NO3− concentrations were 11 times greater than on any other sample date during the study. At these shallow depths, benthic microalgae made a significant contribution to total shelf production, averaging about 14% of total production. These results helped characterize benthic and water column production rates prior to planned habitat alterations caused by placement of numerous artificial reef structures in the region.