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अमूर्त

Structure of the Mesophotic Macroalgal Communities from Offshore Hard Banks in Louisiana before and after the 2010 Deepwater Horizon Oil Spill

Dagoberto E Venera-Ponton*, William E Schmidt and Suzanne Fredericq

The mesophotic macroalgal communities offshore Louisiana, NW Gulf of Mexico are exceptionally biodiverse on hard banks located at 50-100 m depth. Despite their vulnerability to oil spills, little is known about the seasonal and spatial dynamics of these algal communities after the 2010 Deepwater Horizon oil spill (DWH). This study addresses this deficiency by compiling data on macroalgal abundances from 14 research cruises that sampled two offshore banks near the vicinity of the DWH Macondo oil well blowout. Statistical analyses revealed a strong seasonal structure in which environmental changes were followed by community changes after a month. This delayed response was linked to in situ temperatures, coinciding with various studies worldwide reporting temperature as the main predictor of seasonal structure in macroalgal communities. Additionally, this study provides evidence that the DWH may have affected the macroalgal community of Ewing Bank. Summer box dredges launched after the DWH lacked several macroalgal taxa that before the disaster were typically associated with that season; nonetheless, Summer dredges post-DWH showed a greater biodiversity due to the presence of other macroalgae. This biodiversity rise resembled a temporary response rather than a permanent outcome since the increase was statistically significant only during 2011, and seems to have progressively declined towards pre-DWH levels. Conversely, macroalgal composition seems to be progressively diverging from pre-DWH conditions. Importantly, community changes post-DWH are not necessarily caused by spilled oil but may be a consequence of other factors associated with the event.