Post Hurricane Katrina Damage Assessment of Seagrass Resources of the Mississippi Islands - Gulf Islands National Seashore

Byron, Dorothy; Heck, Kenneeth

On November 8th and 9th, 2005, the northern shores of the Mississippi Gulf Islands were surveyed to assess changes in seagrass distribution and abundance that may have occurred after Hurricane Katrina. Of the 51 sites visited along the Mississippi Gulf Islands National Seashore, 33 sites had seagrass present either as a pure stand of Halodule wrightii, a mixed bed of Halodule wrightii and Syringodium filiforme, or a pure stand of Syringodium filiforme. Comparison of the 2005 survey to the Heck et al. (1996) survey showed both decreases and increases in seagrass coverage, with decreases seen mainly at the Ship Islands. Halodule wrightii mean shoot density was 2104 +/- 891 shoots/m2 (+/- s.e.) at East Ship Island, 2287 +/- 231 shoots/m2 at Horn Island, and 3380 +/- 454 shoots/m2 at Petit Bois Island. Aboveground biomass estimates showed decreases at all three islands where seagrass was present, but belowground biomasses showed relatively little changes at East Ship Island and Horn Island and an increase at Petit Bois, indicating that aboveground biomass measurements may be underestimated due to the time of year in which the samples were taken. Finally, we conclude that Hurricane Katrina did not devastate the majority of seagrass beds along the Mississippi Gulf Islands National Seashore, but this was possible only because historical data on the distribution and abundance of seagrass species existed.