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.
Spatial and temporal patterns of colonization by deep-sea hydrothermal vent invertebrates on the Juan de Fuca Ridge, NE Pacific