Abstract:
Sediments associated with hydrothermal venting,
methane seepage and large organic falls such as
whale, wood and plant detritus create deep-sea networks
of soft-sediment habitats fueled, at least in part, by the
oxidation of reduced chemicals. Biological studies at
deep-sea vents, seeps and organic falls have looked at
macrofaunal taxa, but there has yet to be a systematic
comparison of the community-level attributes of sediment
macrobenthos in various reducing ecosystems. Here
we review key similarities and differences in the sediment-dwelling
assemblages of each system with the goals of (1)
generating a predictive framework for the exploration and
study of newly identified reducing habitats, and (2)
identifying taxa and communities that overlap across
ecosystems. We show that deep-sea seep, vent and
organic-fall sediments are highly heterogeneous. They
sustain different geochemical and microbial processes
that are reflected in a complex mosaic of habitats
inhabited by a mixture of specialist (heterotrophic and
symbiont-associated) and background fauna. Community-level
comparisons reveal that vent, seep and organic-fall
macrofauna are very distinct in terms of composition at
the family level, although they share many dominant taxa
among these highly sulphidic habitats. Stress gradients
are good predictors of macrofaunal diversity at some sites,
but habitat heterogeneity and facilitation often modify
community structure. The biogeochemical differences
across ecosystems and within habitats result in wide
differences in organic utilization (i.e., food sources) and in
the prevalence of chemosynthesis-derived nutrition. In
the Pacific, vents, seeps and organic-falls exhibit distinct
macrofaunal assemblages at broad-scales contributing to
ß diversity. This has important implications for the
conservation of reducing ecosystems, which face growing
threats from human activities.
