Drift macroalgal distribution in northern Gulf of Mexico seagrass meadows.

Drift macroalgae, often found in clumps or mats adjacent to or within seagrass beds, can increase the value of seagrass beds as habitat for nekton via added food resources and structural complexity. But, as algal biomass increases, it can also decrease light availability, inhibit faunal movements, smother benthic communities, and contribute to hypoxia, all of which can reduce nekton abundance. We quantified the abundance and distribution of drift macroalgae within seagrass meadows dominated by turtle grass Thalassia testudinum across the northern Gulf of Mexico and compared seagrass characteristics to macroalgal biomass and distribution. Drift macroalgae were most abundant in areas with higher seagrass shoot densities and intermediate canopy heights. We did not find significant relationships between algal biomass and point measures of salinity, temperature, or depth. The macroalgal genera Laurencia and Gracilaria were present across the study region, Agardhiella and Digenia were collected in the western Gulf of Mexico, and Acanthophora was collected in the eastern Gulf of Mexico. Our survey revealed drift algae to be abundant and widespread throughout seagrass meadows in the northern Gulf of Mexico, which likely influences the habitat value of seagrass ecosystems.

Disturbance-driven changes to northern Gulf of Mexico nekton communities following the Deepwater Horizon oil spill.

The 2010 Deepwater Horizon (DwH) oil spill in the Gulf of Mexico discharged ~3.19 million barrels of oil into Gulf waters, making it one of the largest marine disasters in history in terms of volume. We report on the results of a study to assess oil impacts to coastal fishes and invertebrates. Using two-decades of fisheries-independent data in coastal Alabama and Mississippi, we document variability following both natural and anthropogenic disturbances from two periods pre-DwH (1997-2001 and 2007-2009), one intra-spill period for acute DwH effects (2010-2012) and one period post-spill for chronic, longer-term impacts (2014-2017). Results indicated significant changes to community structure, relative abundance, and diversity in the intra-spill period. Causation for changes is confounded by variables such as behavioral emigration, altered freshwater inflow, death of consumers, and the mandated fishery closure. Results highlight the need for long-term, comprehensive monitoring/observing systems to provide adequate background for assessing future disturbances.