New insights on coral mound development from groundtruthed high-resolution ROV-mounted multibeam imaging

Currents play a vital role in sustaining and developing deep water benthic habitats by mobilising food and nutrients to otherwise relatively barren parts of the seabed. Where sediment supply is significant, it can have a major influence on the development and morphology of these habitats. This study examines a segment of the Belgica Mound Province, NE Atlantic to better constrain the processes affecting a small-sized cold water coral (CWC) mound habitat and conversely, the hydrodynamic influence of CWC mounds on their own morphological development and surroundings. Here, we utilise ROV-mounted multibeam, ROV-video data, and sediment samples to investigate current processes, mound morphology, density and development. Detailed mapping shows that the area may have the highest density of coral mounds recorded so far, with three distinct mound types defined based on size, morphology and the presence and degree of distinct scour features. A residual current of 36-40 cm s−1 is estimated while large scour features suggest low-frequency, high-magnitude events. These 3 mound types are i) smaller mounds with no scour; ii) mounds with scour in one to two distinct directions and; iii) larger mounds with mound encircling scour. The differing mound types likely had a staggered initiation where younger mounds preferentially developed near clusters of pre-existing mounds. Given the high density of these small CWC mounds, we support the hypothesis that over time, this clustering may eventually lead to these mounds coalescing into larger coral mound features.