Spatial patterns in benthic seamount habitats: Scales, drivers and effects on biodiversity

Abstract

The deep sea is the largest ecosystem on our planet, but its sheer size and remoteness causes it to be one of the least explored frontiers. One of the most common deep-sea habitat types are seamounts, which are mountains that can elevate thousands of meters above the seabed. For deep-sea fauna, seamounts provide a distinctive setting amongst the surrounding abyssal plains, with their hard substrate, steep slopes and dynamic hydrographies. Only a small fraction of seamounts have been sampled, but many ecological hypotheses have been generated, which suggest that these habitats have an important ecological function in the deep-sea. Here, I investigate a series of seamounts within the Equatorial Atlantic using ROV video footage, CTD and ship-based multibeam data collected during the Tracing Ocean Processes Using Corals and Sediments (TROPICS) research expedition. This thesis presents new data on megabenthic communities and describes ecological and biodiversity patterns in a region in which seamount research has been extremely limited.
The aim of this thesis is to characterise the benthic communities and their diversity patterns on seamounts across the poorly sampled Equatorial Atlantic. More specifically, this work aims to 1) improve the understanding of the beta diversity pattern of seamount megabenthos, 2) understand the basin-wide spatial distribution and biodiversity patterns of cold-water coral taxa on Equatorial Atlantic seamounts and 3) provide a high-resolution biological data set and an ecological insight into a transverse ridge –habitat, which is currently being proposed as an area of conservation in relation to deep-sea mining. The findings suggest that seamounts have high beta diversity, which is dominated by species replacing each other in response to changing environmental conditions, an ecological process, which is likely to enhance the overall biodiversity on seamounts. The new coral data produced in this thesis show that the Equatorial Atlantic seamounts harbour a high number of cold-water coral species, with species richness decreasing east-to west, potentially as a result of a decreasing productivity regime. The data from the transverse ridge reveal a set of complex geomorphologies, which host vulnerable marine ecosystems. The results and data sets from this thesis provide new observations of species from many previously uncharacterised seamounts, which contribute towards the wider biogeography of deep-sea fauna. The findings also provide a platform and basis for future deep-sea exploration and biogeographical studies within the region of the Equatorial Atlantic.

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ORCID for Veerle Huvenne: orcid.org/0000-0001-7135-6360

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