Coral Patch seamount (NE Atlantic) – a sedimentological and megafaunal reconnaissance based on video and hydroacoustic surveys

摘要

The present study provides new knowledge about the so far largely unexploredCoral Patch seamount which is located in the NE Atlantic Ocean half-waybetween the Iberian Peninsula and Madeira. For the first time a detailedhydroacoustic mapping (MBES) in conjunction with video surveys (ROV, camerasled) were performed to describe the sedimentological and biologicalcharacteristics of this sub-elliptical ENE-WSW elongated seamount. Videoobservations were restricted to the southwestern summit area of Coral Patchseamount (water depth: 560–760 m) and revealed that this part of the summitis dominated by exposed hard substrate, whereas soft sediment is just aminor substrate component. Although exposed hardgrounds are dominant forthis summit area and, thus, offer suitable habitat for settlement by benthicorganisms, the benthic megafauna shows rather scarce occurrence. Inparticular, scleractinian framework-building cold-water corals areapparently rare with very few isolated and small-sized live occurrences ofthe species Lophelia pertusa and Madrepora oculata. In contrast, dead coral framework and coral rubble aremore frequent pointing to a higher abundance of cold-water corals on CoralPatch during the recent past. This is even supported by the observation offishing lines that got entangled with rather fresh-looking coral frameworks.Overall, long lines and various species of commercially important fish werefrequently observed emphasising the potential of Coral Patch as an importanttarget for fisheries that may have impacted the entire benthic community.Hydroacoustic seabed classification covered the entire summit of Coral Patchand its northern and southern flanks (water depth: 560–2660 m) and revealedextended areas dominated by mixed and soft sediments at the northern flankand to a minor degree at its easternmost summit and southern flank.Nevertheless, these data also predict most of the summit area to bedominated by exposed bedrock which would offer suitable habitat for benthicorganisms. By comparing the locally restricted video observations and thebroad-scale monitoring of a much larger and deeper seafloor area as derivedby hydroacoustic seabed classification, it becomes obvious that habitatinformation obtained by in situ sampling may provide a rather scatteredpattern about the entire seamount ecosystem. Solely with a combination ofboth methods, a satisfactory approach to describe the diversecharacteristics of a seamount ecosystem can be derived which is in turnindispensable for future scientific monitoring campaigns as well asmanagement and conservation purposes.