Chemosymbiotic specificity and plasticity in thyasirid bivalves

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In marine sediments highly enriched with organic matter (e.g. near pulp and paper mill or sewage outfalls, aquaculture pens, agricultural sites, and gas and oil fields), microbes degrade organic matter, producing toxic reduced sulphur; organic enrichment is recognized as being one of the greatest problems facing coastal environments worldwide. A particular group of small, poorly-known clams (bivalve family Thyasiridae) is often among the first and most abundant colonists of enriched environments, including in several sites along the Canadian coastline. Those thyasirid clams are able to thrive in enriched environments with the help of symbiotic, sulphur-oxidizing bacteria living in their gills; bacterial symbionts are an additional food source for the clams. As opposed to other animals with similar symbioses from deep-sea hydrothermal vents, cold seeps or whale falls, thyasirids do not keep their bacterial symbionts within gill cells, but outside them (extracellularly). My research uses cutting-edge observational techniques to study the particularities of extracellular symbiosis in thyasirid clams, and how it affects the nutritional input they gain from the association. Also, I focus on the variability in symbiont abundance between different sites, and I use experiments in which nutritional inputs to the host and symbiont are manipulated, to determine the impacts on the clams. Finally, I study the identity of the clams and symbionts in different study sites, using molecular approaches. By exploring how a potentially less rigid symbiosis might be beneficial for surviving in changing environments, it is hoped that the role and eventual environmental impacts of thyasirid clams in enriched environments will become clear. This work should be important for marine biologists, government policy decision-makers, and scientists involved in the monitoring of organically enriched sediments; as such, this research is expected to benefit all Canadians through a better understanding of the role of those unique species that are adapted for living in disturbed marine sediments.