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

Shallow continental shelves support productive pelagic and benthic communities. This study characterized a shallow shelf region in the northeastern Gulf of Mexico focusing on the effect of light on water column and benthic fluxes 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 which were used to calculate gross primary production and respiration. Phytoplankton productivity was measured using C-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 d in this study. Maximum rates of phytoplankton production up to 2.7 g C m d occurred in spring. This followed upwelling favorable winds conditions when bottom water NO concentrations were 11 times greater than on any other sample date during the study. At these shallow depths, benthic microalgae make a significant contribution to total shelf production in the northeastern Gulf of Mexico, on average about 14% of total production. These results help characterize benthic and water column production prior to planned placement of thousands of artificial reef structures in the region that will result in habitat alteration.