Are spatial variations in the diets of hydrothermal fauna linked to local environmental conditions?

Abstract

International audienceTrophic relationships in Bathymodiolus azoricus mussel bed communities on the Tour Eiffel hydrothermal edifice (Lucky Strike) were assessed using delta C-13 and delta N-15 signatures from 14 hydrothermal species. The nutritional basis of B. azoricus was also investigated with delta S-34. Faunal samples and environmental data (temperature, pH, total dissolved sulfide, iron and copper concentrations) were collected from 12 different locations on the edifice. Chemical conditions varied between microhabitats, and were all correlated to temperature. Carbon and nitrogen isotopic results revealed the presence of two, apparently independent, trophic groups. The first was composed of symbiont-bearing fauna (B. azoricus and their associated polychaetes Branchipolynoe seepensis), while the second enclosed heterotrophic fauna (bacterivores, cletritivores, scavengers, predators). A majority of mussels displayed delta C-13 values ranging from -27 parts per thousand to -34 parts per thousand, supporting thiotrophy as the dominant nutritional pathway at Tour Eiffel, with methanotrophy and filter feeding emerging as secondary strategies. This result was corroborated by delta S-34 signatures. However, higher delta C-13 values in larger mussels suggested that, as they grow, B. azoricus mussels rely more heavily on their methanotrophic enclosymbionts. Significant spatial variability in isotopic signatures for single faunal species was observed at the scale of the edifice for three species (B. azoricus, B. seepensis, Amathys lutzi), and environmental conditions explained variation in isotopic signatures for one-third of the species. This confirms the hypothesis raised by several authors on the role of hydrothermal fluids on the trophic network at small spatial scales. We suggest that vent fluid characteristics, by influencing microbial production, are key factors in the variation of local carbon sources at vents

Faunal trophic structure at hydrothermal vents on the southern Mohn’s Ridge, Arctic Ocean

“…The results from this isotopic study are thus in agreement with studies showing wide-ranging differences in primary food sources and trophic structure at vents on the Juan de Fuca Ridge (e.g. Limén et al 2007) and the MAR (Vereshchaka et al 2000, De Busserolles et al 2009). Furthermore, large ranges in δ 13 C signatures were detected between different faunal types at these sites as well as within similar taxa from a single box-core or ROV sample.…”

“…These results thus concur with other vent studies in which wide intra-taxon ranges in isotopic signatures have been found (Limén et al 2007, De Busserolles et al 2009. Capitellid polychaetes at both the Troll-LT and -NHT sites comprised some of the isotopically heaviest taxa found.…”

“…High fluxes of labile detritus sinking to the relatively shallow seafloor studied here may contribute to the lack of vent endemism among the benthic fauna (Schander et al 2010), as well as to the reliance of invertebrates on photosynthetic production at the Troll-LT, Troll-NHT, Gall-LT, and Gall-NV sites. The large contribution of photosynthetic production to faunal diets at the 2 LT vents is consistent with studies conducted at shallow seeps in the North Sea (Dando et al 1991), the California shelf and slope (Levin et al 2000), as well as at bathyal depth vents on the MAR (De Busserolles et al 2009) and the Manus Basin (Levin et al 2009). Reproduction in the endosymbiotic Atlantic vent mussel Bathymodiolus azoricus from the Menez Gwen vent site (840 to 850 m depth) correlated with the seasonal phytoplankton peak, further pointing to the importance of photosynthetic material to bathyal-depth vent fauna (Dixon et al 2006).…”

Biological and environmental rhythms in (dark) deep-sea hydrothermal ecosystems

“…They form dense faunal assemblages in relatively low-temperature microhabitats (De Busserolles et al, 2009;Cuvelier et al, 2011a). A spatial segregation in mussel sizes is observed with a decrease in size with increasing distance from hydrothermal input and corresponding thermal gradient showing diet changes with mussel size categories (Husson et al, 2017).…”

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.…”