Population Characteristics and Sulfide Oxidizing Metabolism of the Bivalve \u3cem\u3eSolemya velum\u3c/em\u3e

The physiological and biochemical studies of some animals from sulfide-rich habitats, such as deep sea hydrothermal vents, sewage outfall areas, eelgrass beds and mangrove swamps, have shown that sulfide-oxidizing chemoautotrophic bacteria exist endosymbiotically with the animals and provide a major energy source to their host. One of the remaining questions is the degree to which the symbiont supplies the host\u27s need for reduced carbon and energy metabolism. Solemya velum, a common Atlantic clam from Nova Scotia to Florida, has chemoautotrophic symbionts in the gill tissue (Cavanaugh, 1983). The host animal has a reduced digestive system and lacks some digestive enzymes. The work reported in this thesis was intended to provide information on the population density and growth rate of the species in Ninigret Pond, Rhode Island, and on the energy input, energy output and energy consumption of the animal under the conditions of laboratory measurement. An energy budget based on a number of assumptions was proposed from both field and experimental data. The growth parameters L∞ (length at infinity), K (the rate at which the animal approaches L∞), c (the intensity of the growth oscillations) and WP (winter point) of the seasonal von Bertalanffy growth equation were estimated from the length-frequency of Solemya velum using an objective, computer-aided method (Electronic LEngth Frequency ANalysis, ELEFAN). The results were L∞ = 19.6 mm, K = 0.61, c = 1.0 and WP = 1.1 on a yearly basis. A value of total mortality Z = 2.63 was estimated for the adults from a length-converted catch curve; therefore, the annual survival rate was 7.2% for the population. The highest density of the population 2 was 289 clams/m2, and the average density was 120 2 clams/m2. The other population characteristics, such as length vs. width, · length vs. dry weight, and wet weight vs. dry weight were also described. The enzymatic activities of sulfide oxidation were assayed in the gill tissues of Solemya velum. The maximal activities (Vmax) were 4.7 umoles (substrate converted to product) per gram fresh gill per min for thiosulfate transferase, 2.2 umoles/g/min for adenylylsulfate reductase, and 5.0 umoles/g/min for sulfate adenylyl transferase. The presence of sulfide stimulated and enhanced the respiratory rate of the animal. The animal respiration (65.2 ± 11.2 ul O2/g total wet weight (shell included)/hr) accounted 56.8% of the total oxygen consumption (115.4 ± 18.6 ul while chemoautotrophic symbionts consumed the rest 43.2% (50.2 ul O2/g/hr). An energy budget of Solemya velum, a chemoautotrophic symbiotic association, has been constructed based the growth rate, oxygen consumption and enzymatic activities of the species. The energy derived from sulfide oxidation may account 29% of the total energy input. The other sources of energy, like feeding and dissolved organic uptake, may provide the rest, 71%. The energy loss due to respiration and excretion may account 85% of the input energy, while only 15% may have been used for body growth. Multiple modes of nutrition are suggested for this protobranch bivalve. An energy flow model is proposed for the species, and may be applicable to some deep-sea hydrothermal vent organisms