PARENT SESSION
Poster Session 12: Physiology
Tuesday, August 9, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Dissolved oxygen level as a predictor of fingernail clam (Sphaerium sp.) distribution in a Ugandan papyrus swamp.

Joyner-Matos, Joanna^*,1, Chapman, Lauren², Julian, David¹, ¹ University of Florida, Gainesville² McGill University, Montreal, Quebec, Canada

ABSTRACT- In aquatic habitats, abiotic factors affect species distribution by stressing organisms to their physiological limits. Dissolved oxygen (DO) content, particularly high (hyperoxic) DO levels, can stress organisms by causing increased endogenous production of free radicals, which are highly reactive molecules that cause oxidative damage. To test whether DO levels influence the distribution of aquatic organisms, we combined empirical studies of field distributions, field transplant experiments, and laboratory assays of field-collected specimens of the freshwater bivalve Sphaerium sp., which inhabits papyrus (Cyperus papyrus) swamp/river systems in western Uganda. In this system, ecotonal gradients from normoxia to hypoxia occur along streams feeding into the swamps. A survey of Sphaerium sp. distribution across the swamp-river landscape indicated highest clam abundance in extremely hypoxic swamp waters, despite no apparent physical barrier between the swamp and its tributary streams. A fine-scale study of Sphaerium distribution across a swamp-tribuary ecotone was used to identify the relative importance of DO as a predictor of Sphaerium distribution. Across the ecotonal gradient, DO levels were lowest in the swamp sites (mean DO = 0.82 ± 0.18 mg L^-1), increasing to 3.05 ± 0.07 mg L ^-1 in the ecotone region, and 5.46 ± 0.24 mg L^-1 in the stream sites. In contrast, conductivity, pH, and depth did not vary significantly among the three regions of the transect. Average clam density was high but patchy in the swamp, with an overall mean of 74.9 ± 15.4 clams per 0.5 m² and ranging from 8 to 246 clams per 0.5 m². Clam densities decreased along the ecotone, and clams were completely absent in the stream sites. Sphaerium sp. abundance was negatively correlated with DO across sampling sites (r = -0.72, p = 0.002). Transplant experiments were used to explore the physiological consequences to Sphaerium of exposure to normoxic waters. Analysis of a general stress indicator (glycogen content) and expression levels of stress proteins that minimize oxidative damage will be conducted to assess whether transplant to ecotonal and stream sites resulted in oxidative damage associated with hyperoxia.

Key words: hypoxia, distribution, Sphaerium, swamp