Protozoans Isolated from Louisiana Shelf Sediments Subject to Hypoxia/Anoxia with Emphasis on Freshwater Amoebae and Marine Flagellates

Sediments offshore from the Louisiana coast west of the Mississippi Delta Bight were cultured for marine and freshwater protozoans during a period of seasonal benthic hypoxia. The episodes of hypoxia occurring in this area from late spring through early fall follow periods of high volume discharge from the Mississippi River, and coincide with a strong pycnocline between low salinity surface water and deeper more saline water. The study site was located off the Terrebonne/Timbalier Bay system at depths of 14-22 m where there are recurrent episodes of dissolved oxygen readings approaching 0.0 mg L-1, and bottom water and sediments may have an odor of hydrogen sulfide. Sewage contamination at the site has been considered since there are numerous point and non-point sources for pollutants that enter the ecosystem from nearby rivers and bays. We tested bottom sediments to determine whether or not freshwater, soil, or sewage associated protozoans were present as indicators of land or riverine runoff. Two of seven sediment samples yielded freshwater or soil cyst-forming amoebae belonging to the genus Acanthamoeba (A. polyphaga and A. hatchetti); one yielded a cyst-forming freshwater flagellate, Heteromita globosa. All stations were positive for one or more of 15 genera of marine flagellates, four yielded unidentified ciliates and five free-living marine amoebae. Physical features of the seabottom and observations on the benthic biota observed by divers and Remotely Operated Vehicles (ROVs) showed that surficial sediments were anoxic and covered by bacterial mats.