Different processes and constraints drive the assembly of deep-sea hydrothermal vent and sunken wood communities

Abstract

Niche processes mainly dictate the successful establishment and coexistence of species along gradients of community drivers such as energy availability and environmental stress. Deep-sea chemosynthetic habitats such as hydrothermal vents and wood falls show concomitant gradients of energy availability and stress because productivity is fueled by potentially toxic, chemically reduced compounds. However, the specific processes and constraints driving the assembly of these eco-evolutionarily related communities remain poorly understood. Here, we infer community assembly processes from species, functional, and isotopic diversity patterns of vent and wood-fall assemblages using a colonization experiment along a hydrothermal gradient, from vent periphery to diffuse-flow habitats. We hypothesized that despite the high environmental stress, the high productivity of vent diffuse-flow and wood-fall habitats increases niche space due to niche partitioning and/or competitive exclusion processes, allowing more species to coexist in high densities. As predicted, at moderate levels of stress at vent diffuse-flow habitats, productivity increases niche space and supports denser and more species-rich assemblages with many ecological strategies, suggesting niche partitioning and/or competitive exclusion of functionally similar species. However, as stress increases at habitats under higher venting influence, species richness, abundance, and functional diversity decrease, suggesting environmental filtering and/or competitive dominance of better adapted species. Similarly, the vent periphery supports fewer species, individuals, trophic levels, and reduced niche space, suggesting that the scarcer food resources act as an environmental filter. Unexpectedly, food resources at wood substrata at the vent periphery, harboring typical wood-fall communities, support very speciose and dense assemblages of reduced functional diversity. This suggests that compared to vent diffuse-flow habitats, the reduced habitat availability, or longevity, of wood falls reduces niche space and promotes environmental filtering and/or competitive dominance processes. Thus, different processes and constraints appear to drive the assembly of communities along hydrothermal vent gradients and between the eco-evolutionarily related vent and wood-fall communities.