Abstract
Abstract. Hydrothermal vent sites along the Juan de Fuca Ridge in the north-east Pacific host dense populations of Ridgeia piscesae tubeworms that promote habitat heterogeneity and local diversity. A detailed description of the biodiversity and community structure is needed to help understand the ecological processes that underlie the distribution and dynamics of deep-sea vent communities. Here, we assessed the composition, abundance, diversity and trophic structure of six tubeworm samples, corresponding to different successional stages, collected on the Grotto hydrothermal edifice (Main Endeavour Field, Juan de Fuca Ridge) at 2196 m depth. Including R. piscesae, a total of 36 macrofaunal taxa were identified to the species level. Although polychaetes made up the most diverse taxon, faunal densities were dominated by gastropods. Most tubeworm aggregations were numerically dominated by the gastropods Lepetodrilus fucensis and Depressigyra globulus and polychaete Amphisamytha carldarei. The highest diversities were found in tubeworm aggregations characterised by the longest tubes (18.5 ± 3.3 cm). The high biomass of grazers and high resource partitioning at a small scale illustrates the importance of the diversity of free-living microbial communities in the maintenance of food webs. Although symbiont-bearing invertebrates R. piscesae represented a large part of the total biomass, the low number of specialised predators on this potential food source suggests that its primary role lies in community structuring. Vent food webs did not appear to be organised through predator–prey relationships. For example, although trophic structure complexity increased with ecological successional stages, showing a higher number of predators in the last stages, the food web structure itself did not change across assemblages. We suggest that environmental gradients provided by the biogenic structure of tubeworm bushes generate a multitude of ecological niches and contribute to the partitioning of nutritional resources, releasing communities from competition pressure for resources and thus allowing species to coexist.
Highlights
Deep-sea hydrothermal vents occur along mid-ocean ridges and back-arc spreading centres, which are characterised by strong volcanic and tectonic activity
The objectives of the present study were (i) to identify the composition and structure of three faunal assemblages associated with R. piscesae tubeworm bushes on the Grotto hydrothermal edifice, with respect to density, biomass and species diversity, (ii) to characterise the trophic structure of these biological communities, and (iii) to assess how diversity and trophic relationships vary over different successional stages
This study provides the first characterisation of the structure, species diversity and food web structure of macrofaunal assemblages living in Ridgeia piscesae tubeworm bushes on the Grotto hydrothermal edifice
Summary
Deep-sea hydrothermal vents occur along mid-ocean ridges and back-arc spreading centres, which are characterised by strong volcanic and tectonic activity. The resulting hydrothermal fluid fosters dense communities of highly specialised fauna that colonise the steep physical and chemical gradients created by the mixing of hot vent fluids with cold seawater. These communities are distributed according to species’ physiological tolerance (Childress and Fisher, 1992; Luther et al, 2001), resource availability (De Busserolles et al, 2009; Levesque et al, 2003) and biotic interactions The fauna are highly dissimilar between oceanic basins (Bachraty et al, 2009; Moalic et al, 2011), hydrothermal communities throughout the world share some ecological similarities including a food web based on chemosynthesis (Childress and Fisher, 1992), low species diversity compared with adjacent deep-sea and coastal benthic communities (Van Dover and Trask, 2000; Tunnicliffe, 1991), high levels of endemism (Ramirez-Llodra et al, 2007), and elevated biomass associated with the presence of large invertebrate species
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