Picturing thermal niches and biomass of hydrothermal vent species

Abstract

In community ecology, niche analysis is a classic tool for investigating species' distribution and dynamics. Components of a species' niche include biotic and abiotic factors.In the hydrothermal vent ecosystem, although composition and temporal variation have been investigated since these deep-sea habitats were discovered nearly 40 years ago, the roles and the factors behind the success of the dominant species of these ecosystems have yet to be fully elucidated. In the Lucky Strike vent field on the Mid Atlantic Ridge (MAR), the dominant species is the mussel Bathymodiolus azoricus. Data on this species and its associated community were collected during four oceanographic cruises on the Eiffel Tower edifice and integrated in a novel statistical framework for niche analysis. We assessed the thermal range, density, biomass and niche similarities of B. azoricus and its associated fauna.Habitat similarities grouped mussels into three size categories: mussels with lengths ranging from 0.5 to 1.5 cm, from 1.5 to 6 cm, and mussels longer than 6 cm. These size categories were consistent with those found in previous studies based on video imagery. The three size categories featured different associated fauna. The thermal range of mussels was shown to change with organism size, with intermediate sizes having a broader thermal niche than small or large mussels. Temperature maxima seem to drive their distribution along the mixing gradient between warm hydrothermal fluids and cold seawater. B. azoricus constitutes nearly 90% of the biomass (in g dry weight /m²) of the ecosystem. Mean individual weights were calculated for 39 of the 79 known taxa on Eiffel Tower and thermal ranges were obtained for all the inventoried species of this edifice. The analysis showed that temperature is a suitable variable to describe density variations among samples for 71 taxa. However, thermal conditions do not suffice to explain biomass variability. Our results provide valuable insight into mussel ecology, biotic interactions and the role of B. azoricus in the community.

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). Contrastingly to what has been described by Sarrazin et al (2014), no significant interactions between mussels and other organisms were observed based on the 6 h frequency analysed here.…”

Replies to Short Comment

“…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). Contrastingly to what has been described by Sarrazin et al (2014), no significant interactions between mussels and other organisms were observed based on the 6 h frequency analysed here.…”

Dispersion of deep-sea hydrothermal vent effluents and larvae by submesoscale and tidal currents

“…Four species of Bathymodiolus inhabit vent sites on the MAR (Van Cosel et al, 1999;van der Heijden et al, 2012). PLDs of Bathymodiolus mussels vary 500 from 3-4 months for the dominant species on the northern MAR Bathymodiolus azoricus (Colaço et al, 2006;Husson et al, 2016), to more than a year for Bathymodiolus childressi (Arellano and Young, 2009). As Bathymodiolus' eggs are slightly negatively buoyant (although not precisely quantified, Arellano and Young, 2009), they are not likely to spread upon release otherwise than through 505 their entrainment in the rising vent plume, which extends 300-500 m above the source (Speer and Marshall, 1995;Wilson et al, 1996).…”

“…Considering their egg size and body length, Bathymodiolus fecundity can reasonably be assumed to be at least in the same order of magnitude as in coastal mytilids, which can release more than 10 6 eggs/female/spawning season (Sprung, 1983). The average 570 density of sexually mature mussels (i.e., exceeding 3 cm body length, Colaço et al, 2006) is 10 3 ind m −2 (Cuvelier et al, 2011a;Husson et al, 2016), half of them being females. Estimating the surface covered by these mussels to be about 10 m 2 in Eiffel Tower (Figure 3 in Cuvelier et al (2009) andCuvelier et al (2011b)), we grossly estimate that 5000 mature females may spawn their 575 eggs each season at this edifice.…”