Habitat characterization and nutritional strategies of the endosymbiont-bearing bivalve Lucinoma aequizonata

Abstract

A population of the lucinid bivalve Lucinorna aequizonata, with sulfur-oxidizing endosymbiotic bacteria in the gills, is restricted to a narrow depth range (500 -f-10m) on the slope of the Santa Barbara Basin, California, USA. In this zone, the seawater just above the substratum is sub-oxic ( [ 0 2 ] < 2 0 F M ) . The organically rich sediments in which these clams live are well mixed by bioturbation, which appears to maintain a redox condition Limiting the extensive accumulation of hydrogen sulfide. However, thiol levels in the blood of the clams indicate an exposure to significant amounts of sulfide and/or thiosulfate apparently from randomly &spersed short-lived pockets of sulfidic mud that can b e reached by the clam's burrowing vermiform foot. When the bivalves are incubated in the presence of hydrogen sulfide, thiosulfate is concentrated in the blood and apparently utilized by the bacteria for metabohc energy and the production of intracellular elemental sulfur. Laboratory growth experiments demonstrated that sulfide concentrations greater than 10 F M were detrimental to the host, even though the bacteria continued to accumulate elemental sulfur. The utilization of thiosulfate under near anaerobic conditions and the accumulation of intracellular elemental sulfur by the endosymbiotic bacteria coupled with the high availability of environmental nitrate and low molecular oxygen suggests a metabolic strategy analogous to the free-living sulfur oxidizer Thlobacillus denjtrificans. The 6 ' 3~ values of the purified endosymbiont bacteria (-34.0 5 0.8%) were significantly lighter than those of the host tissue (-29.0 + 0.7 %) suggesting that in addition to the nutrition provided by the bacteria, over 25 % of the host carbon may b e attributed to exogenous dissolved carbon which is in high concentrations in its natural habitat.

Identification of food sources of invertebrates from the seagrass Zostera marina community using carbon and sulfur stable isotope ratio and fatty acid analyses

“…The gills, containing symbionts, had significantly (p = 0.01) less 13 C than other body tissues (Table 4), evidently due to the presence of a huge amount of 13 C-depleted bacteria. Sulfur-oxidizing chemoautotrophic bacteria discriminate heavy carbon isotopes to a greater degree than do marine photoautotrophs (Ruby et al 1987), and very low δ 13 C values (-34.0 to -31.7 ‰) were shown for sulfur-oxidizing bacteria isolated from symbiont-bearing bivalves (Cary et al 1989, Conway et al 1989.…”

“…Contribution of chemoautotrophs to Pillucina pisidium feeding was calculated, using δ 13 C values for symbiotic bacteria (mean = -33 ‰) (Cary et al 1989, Conway et al 1989) and suspended POM (-20.9 ‰) as endmembers in Eq. (2).…”

Effects of hydrogen sulfide on the feeding activity of Manila clam Ruditapes philippinarum

“…Marine invertebrates inhabiting H 2 S-rich marine sediments have acquired a variety of biochemical adaptations to detoxify this poisonous compound (Vismann 1991, Baga ri nao 1992 Völkel 1998). In marine bivalves, sulfide is metabolized to less toxic or non-toxic compounds through oxidizing cell tissue activity (Cary et al 1989, O'Brien & Vetter 1990. Thus, bivalves could tolerate H 2 S if their body tissue were oxygenated.…”

Response of seafloor ecosystems to abrupt global climate change

“…These forms are metazoan extremophiles and are characteristic of the most sulfiderich, methane-rich, and oxygen-poor environments of modern continental margins (35)(36)(37). Many of these extremophiles are opportunistic, weedy species and appear in high-density (∼900 individuals/m 2 ) zonations on modern continental margins (22,(38)(39)(40). Deposit feeding, suspension feeding, and detritivorous and carnivorous trophic guilds are also present within the molluscan assemblage.…”