Sedimented Chemosynthetic Ecosystems of the Southern Ocean

Sedimented chemosynthetic ecosystems (SCEs) are complex seafloor environments that combine several potential sources of organic matter. Their physical similarity to the vast soft-sediment habitats on the seafloor means that they can be inhabited by a diverse range of more ubiquitous fauna. This is in stark contrast to ecosystems such as hard substratum hydrothermal vents, which are typically almost totally dominated by a few specialist species. Another characteristic of these ecosystems is that they exhibit diffuse environmental gradients, relating to chemosynthetic production potential and environmental toxicity. Consequently, it is often difficult to determine their spatial extent, and the ecological responses along such gradients. A central theme of the research presented in this thesis has been to determine the role of habitat-structuring processes at two contrasting SCEs in the Atlantic sector of the Southern Ocean. I demonstrate that these environments elicit significant changes in assemblage structure, trophodynamics and carbon cycles. Chemosynthetic activity generally did not constitute a major proportion of the diet of any assemblage, even at the most hydrothermally active sites, but was detected in macrofaunal food webs at very surprising distances (~ 100km) from the (known) sites of active venting. This research illustrates and examines the impacts that these environments can have upon a range of ecological processes and raises questions about the full extent and significance of chemosynthetic organic matter production in seafloor ecosystems.