The Charlie-Gibbs Fracture Zone: megabenthic biodiversity, community composition and their environmental drivers

Abstract

The Charlie-Gibbs Fracture Zone (CGFZ) is a topographically unique area on the Mid Atlantic Ridge (MAR) with numerous bathymetric features which create a heterogenous environment, optimal for the colonisation of cold-water sponge and corals. Previous studies have analysed the megabenthic communities North and South of the fracture zone, but not between the two parallel faults themselves. The region which was surveyed for this study is within the CGFZ North Marine Protected Area (MPA), where the benthic habitats currently remain unprotected from anthropogenic activities. This thesis aims to describe the biodiversity patterns and community composition of the CGFZ as well as their environmental drivers. We use video footage from five transects collected using a Remotely Operated Vehicle and multivariate statistical methods. Over 154,509 individual organisms belonging to 309 megafaunal morphospecies were identified from the video which covered almost 34 km of transect. Using species accumulation curves and generalized additive modelling, depth, slope and the presence of hard substratum were determined to be important factors in the distribution of megafaunal species richness and abundance. When the megafaunal community composition was examined, eight distinct communities were identified, all with multiple Vulnerable Marine Ecosystem indicator species present. These included but were not limited to a sea pen field alongside an Acanella sp. garden, and a community dominated by corals including the black coral Stichopathes sp., soft corals like Anthomastus sp., and scleractinians. Depth, slope and rugosity played a significant role in their differentiation and distribution of these communities. These results will help to inform the future decision making for this region, the CGFZ North MPA, where its protection status will come into debate in the next five years.