Size-dependent variations on the nutritional pathway of Bathymodiolus azoricus demonstrated by a C-flux model

Abstract

Bathymodiolus azoricus is a mussel from vent fields in the southwest of the Azores Triple Junction (Mid-Atlantic Ridge-MAR). Experimental evidence indicates that B. azoricus is a mixotrophic organism, which obtains energy from a dual endosymbiosis and filter-feeding. Yet the relative contribution of symbiosis and filter-feeding to B. azoricus nutrition is still unclear. To address this question, we developed and individual-based model which describes sulphide and methane uptake by endosymbionts, the energy gained through microbial oxidations, the transfer of energy from endosymbionts to B. azoricus, filter-feeding of particulate organic matter (POC) by B. azoricus and the energetic wastes of the mytilid with respiration. The model accounts for size-dependent relationships obtained from empirical data. External concentrations of H 2 S and CH 4 correspond to estimated values for the Menez Gwen vent field, maximal and minimal values measured at MAR. From in situ observed densities of B. azoricus, productivity predictions at the individual level were upscale to the mytilid population at Menez Gwen and compared to estimated values. Predicted biomass of B. azoricus and its endosymbionts show a very high fitting level with estimated values. Results suggest that the relative contribution of filter-feeding and endosymbiosis varies with B. azoricus size, with small mytilids being strongly dependent on filter-feeding, whilst larger mussels obtain a significant portion of its energy from endosymbiosis. This is related with the variation of gill weight with total weight. Results also suggest that, an individual of a certain size can potentially regulate the relative contribution of filter-feeding and endosymbiosis according to external conditions. However, large B. azoricus exhibit a higher level of nutritional flexibility than small mytilids. The relative contribution of endosymbioisis and filter-feeding to the total energy budget of B. azoricus, as well as the mytilid particulate organic matter requirements, are assessed and discussed under several scenarios.

Picturing thermal niches and biomass of hydrothermal vent species

“…Therefore, the presence of large mussels in warm temperature habitats is consistent with previous results (De Busserolles et al, 2009) highlighting changes in trophic diet, from a preferentially sulphide-based nutrition for smaller mussels to a preferentially methane-based nutrition for larger ones. It is also consistent with results (Martins et al, 2008) hypothesizing a shift from particle filtration in small mussels to symbiotic food sources in larger individuals.…”

Community dynamics over 14 years at the Eiffel Tower hydrothermal edifice on the Mid‐Atlantic Ridge

“…obs.). Larger mussels may have a higher physiological adaptability or tolerance of environmental conditions and fluctuations than smaller individuals (Company et al 2007;Martins et al 2008;De Busserolles et al 2009) and thus might be able to survive closer to the fluid exits.…”

Astonishing Fungal Diversity in Deep‐Sea Hydrothermal Ecosystems: An Untapped Resource of Biotechnological Potential?

“…Symbioses between B. azoricus and sulfur-oxidizing and methane-oxidizing bacteria have been demonstrated (Cavanaugh et al, 1987;Duperron et al, 2006); this dual symbiosis allows the host to colonize sulfide-and/or methane-rich environments. Recently, B. azoricus was characterized as a mixotrophic organism, which obtains energy from both its symbionts and from filter-feeding, at a ratio that depends on the mussel size (Martins et al, 2008). The establishment of these endosymbionts may be a long process that is facilitated by filterfeeding at early development stages (small mussels), with an energetic-source switch appearing for only the larger mytilids.…”