Chemosynthesis thrives in a variety of marine benthic ecosystems at all depths of the oceans. Entire animal communities have learned to live with one of the most toxic chemicals - hydrogen sulfide. It pays off because food is plenty. Autotrophic microbes fix inorganic carbon powered by sulfide and other reduced chemicals and animals feed on them directly or even farm them in or on their body. In these nutritional-based, symbiotic mutualisms between sulfur-oxidizing chemoautotrophic (thiotrophic) bacteria and eukaryotes, the host provides inorganic nutrients to the symbiont and receives fixed organic carbon in return. These associations often act as foundation species ameliorating abiotic conditions through uptake of sulfide and providing highly structured habitat for an associated fauna. Both types of positive interactions - symbiotic mutualism and foundation species - are the center of interest of the marine benthic ecology lab.

We focus on two symbiotic mutualisms to test and further develop models on the ecology and evolution of interspecies cooperation. Both systems are simple dual partnerships with a single microbial partner. The giant tubeworm Riftia pachyptila and Cand. Endoriftia persephone lives at deep-sea hydrothermal vents at the East Pacific Rise and the colonial ciliate Zoothamnium niveum and Cand. Thiobius zoothamnicola occurs on shallow-water wood fall in the Adriatic Sea. 

While symbiont transmission is vertical in the colonial ciliate, it is horizontal in the giant tubeworm. Mutualism is facultative for the colonial ciliate. Induced by the presence or absence of the symbiont the host exhibits polyphenism. In contrast, mutualism is obligate for the giant tubeworm, but facultative for the symbiont with loner populations in the vent and surrounding deep-sea environment. Hence, both systems differ in symbiont location (ecto- versus endosymbiont), dependency (facultative versus obligate host, facultative versus obligate symbiont), and transmission (vertical versus horizontal) and therefore are suitable to investigate the impact of these traits on the establishment, maintenance and persistence of symbiotic mutualism. 

We currently investigate recruitment, growth and decay of populations in experiments at deep-sea hydrothermal vents and shallow-water wood falls in situ and use high-pressure and ambient pressure flow-through systems to follow host and symbiont fitness under varying conditions in vivo.