Submerged aquatic vegetation (SAV) provides many critical ecosystem services, yet we lack basic information on SAV assemblages, biomass and diversity across expansive coasts such as the northern Gulf of Mexico (nGoM). This research investigated SAV along the nGoM from 2013-2015 examining (1) inter-annual variation in SAV assemblages and biomass across salinity zones and gulf coast eco-regions (Texas Mid-Coast, Texas/LA Chenier Plain, Louisiana Delta, MS/AL), (2) intra-annual variation in SAV assemblages and biomass across salinity zones, (3) response of two species, Ruppia maritima and Myriophyllum spicatum, to salinity and light regimes, and (4) estimated organic carbon stock and storage of SAV habitat soils across salinity zones. Coast wide, there was no variation among years, but significant differences in biomass and diversity within zones and regions were observed. Specifically, fresh zones and the Louisiana delta region had higher species diversity and contained more biomass than other zones and regions. Intra-annually, there were significant differences in SAV biomass and assemblages by salinity zone and month. Fresh/ intermediate zones contained more species and biomass than brackish/saline zones, and biomass was higher in summer months than winter months. Competitive relationships between co-occurring species were examined using M. spicatum and R. maritima growth response, under different salinity and light regimes. M. spicatum growth decreased with increasing salinity, while R. maritima growth was not impacted. R. maritima was also not impacted by light, while M. spicatum growth increased in high light. We observed strong competitive interactions; both species decreased in mixture and under no conditions was production in mixtures greater than monocultures. We estimated organic carbon stocks (Corg) within Mississippi River Delta Plain (MRDP) SAV habitat, out to the Chandeleur Islands, and found that MRDP SAV Corg did not differ across salinity zones, but was greater than Chandeleur SAV Corg. MRDP SAV habitat (159,609 ha) contains greater than 3.2 * 107 Mg of Corg, representing an unaccounted for reservoir of “blue carbon,” particularly when extrapolated across the Gulf Coast. These new data provide a better understanding of factors controlling SAV spatial distribution, temporal variation and ecosystem services, which helps managers prepare for coastal changes. This project was co-funded by the Gulf Coast Prairie and the Gulf Coastal Plains and Ozarks Landscape Conservation Cooperatives and the South Central Climate Adaptation Science Center.
