SPEAR, E.; ELLIOTT, J.K.; WYLLIE-ECHEVERRIA, S.*; University of Puget Sound; University of Puget Sound; University of Washington: Using the sulfide-oxidizing bacterium Beggiatoa as an indicator of inhibiting levels of hydrogen sulfide for Zostera marina

Seagrass beds are important components of marine ecosystems, but they are in decline worldwide been because of human activity. Environmental organizations are interested in identifying areas that are best suited for seagrass restoration. The objective of this study was to determine the distribution and abundance of the seagrass Zostera marina in relation to the distribution of the mat forming bacterium Beggiatoa spp., and the levels of sulfide and organic material (wood waste) in the sediment. Underwater videography and intertidal surveys were used to map the distribution and abundance of Z. marina beds and Beggiatoa in the nearshore area of Commencement Bay, WA, a location that has a long history of sawmill activity. Z. marina occurred from the intertidal to -6 m MLLW on sandy substrates in areas with low levels of sulfide (< 50 �M) and organic material (< 5 % total volatile solids). Areas with high sulfide levels (> 200 �M) occurred where there were significant amounts of organic material in the sediments, which was found to be wood waste that had been discarded from sawmills that operated on the Tacoma waterfront between 1869-1977. Z. marina was absent from the intertidal and occurred at lower densities in areas with high sulfide levels. In contrast, the bacterium Beggiatoa was only found in areas where the sulfide levels were > 1000 �M and there were significant deposits of wood. Thus, the negative correlation between the distribution and abundance of Z. marina and Beggiatoa, suggests that the presence of Beggiatoa mats could be used as a biological indicator of inhibiting levels of hydrogen sulfide in the marine environment. Sulfide is a phytotoxin, and high levels in sediments have been linked to seagrass die-offs in Florida Bay. This study exemplifies the need to examine the ongoing effects of past human disturbances and suggests that restoration of the nearshore habitat in Commencement Bay will require the removal of wood waste.