Explaining cold-water coral community assembly with seabed and hydrodynamic features

Abstract

Cold-water coral reefs, serving as biodiversity hotspots in the deep sea, can form into carbonate mounds, which are important oceanographic structures with great ecological values. Reef-forming corals and their associated community can display different distribution patterns between mounds, which are hypothesized to be governed by the interactions between the reef community and the environment, i.e. seabed topography and hydrodynamics. In this study, we aimed to investigate the spatial variation of the cold-water coral community distribution, including the inter-mound and intra-mound variation, and explain the community distribution with seabed topographical and hydrodynamic variables. Community assembly data was acquired from remotely operated vehicle (ROV) videos; topographical variables were calculated from multi-beam map, and hydrodynamic variables were extracted from model outputs. Two multivariate statistical analyses, between-class analysis (BCA) and co-inertia analysis were applied to investigate the inter-mound and intra-mound variation of reef community, and the relationship between topographical and hydrodynamic variables and reef community data, respectively. Our results show that community generally concentrates at the summit of smaller mounds, while at the upper flank of larger mounds, implying a potential of vertical growth for small mounds and a steady state of that for larger mounds; endemism was observed on mound scale; reef-forming corals, zoanthids, black corals Antipatharia, and soft corals Alcyonacea are associated with bathymetric position index (BPI), but have no correlation or negative correlation with current speed, implying that these faunal groups cannot effectively capture food particles in high-speed ambient currents; demosponges are positively correlated with slope steepness and horizontal current speed, implying that they use current-induced waterflows to save energy. To further provide insights regarding cold-water coral reef ecosystems, regional-scale biochemistry related to cold-water coral reef and the niche studies of mound-scale endemic species are suggested for the future research.