Carbon Incorporation and Transfer in Marine Worms

Gutless oligochaetes belonging to the phyla Annelida are found widely distributed in various habitats around the world. These worms are unique from other gutless worms because in addition to lacking a gut, mouth and anus they also lack execratory organs. They are therefore dependent on their symbionts for nutrition as well as waste management. In this study species of gutless oligochaetes, Olavius spp., from siliceous sediments near sea-grass beds off the coast of the island of Elba, Italy were investigated. Three species of Olavius spp. worms have been identified on Elba; Olavius algarvensis, Olavius ilvae and one yet to be described species. The two main species, O. algarvensis and O. ilvae harbor sulfur-oxidizing and sulfate-reducing symbionts. Under oxic conditions, the sulfur- oxidizing gammaproteobacterial symbionts are able to use oxygen as an electron acceptor and reduced sulfur as an electron donor for fixation. Inorganic carbon fixation rates have been investigated and calculated for Olavius spp. worms from tracer incubations by Bergin (2009). Transfer of fixed carbon ( 13 C) from symbionts to symbiont-free host tissue was also investigated with nanoSIMS but could not be shown by Bergin (2009). Due to wide variability between individuals, a large number of worms would need to be investigated from tracer incubations to reach a conclusion. Because nanoSIMS is a time consuming method, another method that would allow analyzing large number of samples within a relatively shorter time was needed. In this master’s thesis, tracer incubations were done on Olavius spp. worms to analyze the uptake of labeled inorganic carbon over incubations times. Parallel unlabeled incubations for measuring of dissolved inorganic carbon concentrations were also set up. Microautoradiography was tested as an alternative method for analyzing two aspects; (i) where in the worms carbon was being fixed and (ii) whether there was transfer into central parts of the worms. After tracer incubation experiments, worms were observed to have taken up label from the medium. There was an increase in the concentration of dissolved inorganic carbon in the incubation medium. Microautoradiography revealed that label was mostly located on sections of the worm where the symbionts were located.The results of this thesis show and confirm the findings of Bergin (2009) that the Gamma 1 symbionts of Olavius spp. worms fix carbon when transferred from hypoxic incubations to oxic incubations, without an external sources of energy. The net increase in dissolved inorganic carbon concentration also suggested that more respiration than fixation took place under the given conditions. Although it was not possible to see transfer from the microautoradiography, these experiments revealed important improvements that could be done for the optimization of the method