Methane mussels (Bathymodiolus sp., undescribed; personal communication by R. Turner to CRF) were collected in September 1989 and April 1990 from offshore Louisiana in the Gulf of Mexico. These mussels contain endosymbiotic methane-oxidizing bacteria and are capable of utilizing environmental methane as a source of energy and carbon. Oxygen consumption, methane consumption, and carbon dioxide production were measured in mussels with intact symbionts, functionally aposymbiotic mussels, and separated symbiont preparations under controlled oxygen and methane conditions, in order to study the roles of the symbionts and the hosts in methane utilization. The association was found to be very efficient in fixing methane carbon (only ∼30% of CH4 consumed is released as CO2), and to be capable of maximal rates of net carbon uptake of nearly 5 μmol g-1 h-1. Rates of oxygen and methane consumption were dependent upon oxygen and methane concentrations. Maximal consumption rates were measured at 250 to 300 μM O2 and 200 to 300 μM CH4, under which conditions, oxygen consumption by the gill tissues (containing symbionts) had increased more than 50-fold over rates measured in the absence of methane. A model is proposed for the functioning of the intact association in situ, which shows the symbiosis to be capable of achieving growth rates (net carbon assimilation) in the range of 0.003 to 0.50% per day depending upon oxygen and methane concentrations. Under the conditions measured in the seep environment (200 μM O2, 60 μM CH4), a mussel consuming methane at rates found to be typical (4 to 5 μmol g-1 h-1) should have a net carbon assimilation rate of about 0.1% per day. We suggest that the effectiveness of this symbiosis arises through integration of the morphological and physiological characteristics inherent to each of the symbiotic partners, rather than from extensive specialization exhibited by other deep-sea chemotrophic associations.
All Science Journal Classification (ASJC) codes
- Ecology, Evolution, Behavior and Systematics
- Aquatic Science