Brian J. Roberts, Ph.D.
Executive Director and Chief Scientist
LUMCON

I. Introduction.  LUMCON was created in 1979 with a mission to promote, facilitate and conduct research and education collaborations among Louisiana’s universities in marine and coastal sciences relevant to the sustainability of coastal and marine environments of the Gulf of Mexico. It began operation from five research trailers place atop the marshland at the end of LA Hwy 56 in Cocodrie.  A state-of-the-art Defelice Marine Center opened in 1983, and forty years later a new Blue Works facility on the Houma Maritime Campus opened its doors to provide a nexus for innovation and collaboration between science, education, industry, and community.

II.  Sand Shoal Responses to Dredging.  We assessed the impacts of dredging on benthic primary production, benthic infauna, and nekton as integral components of the food webs on Ship Shoal off the Louisiana coast via a modified Before-After Control Impact design in three sites within each of three regions during three seasons of 2021 and 2022. Peak potential Gross Primary Production (GPP) and light availability decreased with dredge pit depth, resulting in daily-integrated benthic GPP being up to an order of magnitude lower in relic, deeper (~12m) pit than reference regions (~8m), with new, shallower (~10m) pit exhibiting intermediate rates. Benthic respiration also increased with dredge depth and age resulting in the sediments becoming increasingly net heterotrophic, which coincided with observations of bottom water hypoxia in the deeper, mature dredge pit. The new pit had reduced benthic invertebrate biomass by 80%, species richness by 30%, increased number of individuals by 300% relative to reference sites and shifted the community towards the older, deeper pit community but remaining intermediate. Seasonality drove changes in community composition and energy use of nekton assemblages with seasonal fluxes influencing local impacts of dredging, which were disparate among resident consumer species and dependent on time since dredging. In summary, the new pit showed intermediate impacts from dredging compared to those seen in the older pit leading to the question of whether the observed differences are a result of time since dredging, depth of dredging, or a combination of both.