The influence of near-bed hydrodynamic conditions on cold-water corals in the Viosca Knoll area, Gulf of Mexico

• Published in: Deep-sea research. Part I, Oceanographic research papers Oceanographic research papers, 2012, Vol.60, p.32-45
• Main Authors: Mienis, F., Duineveld, G.C.A., Davies, A.J., Ross, S.W., Seim, H., Bane, J., van Weering, T.C.E.
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; Calcium carbonate; Coral reefs; Corals; Ecosystem engineers; Environmental constraints; Fluid mechanics; Foods; Fundamental and applied biological sciences. Psychology; Gulf of Mexico; Habitats; Lophelia pertusa; Marine; Marine ecology; Ocean currents; Oceanography; Origins; Salinity; Sea water ecosystems; Sediments; Synecology; Viosca Knoll
• ISSN: 0967-0637; 1879-0119
• DOI: 10.1016/j.dsr.2011.10.007

Near-bed hydrodynamic conditions were recorded for almost one year in the Viosca Knoll area (lease block 826), one of the most well-developed cold-water coral habitats in the Gulf of Mexico. Here, a reef-like cold-water coral ecosystem, dominated by the coral Lophelia pertusa, resembles coral habitats found off the southeastern US coast and the North East Atlantic. Two landers were deployed in the vicinity and outside of the coral habitat and measured multiple near-bed parameters, including temperature, salinity, current speed and direction and optical and acoustic backscatter. Additionally, the lander deployed closest to the coral area was equipped with a sediment trap that collected settling particles over the period of deployment at 27 day intervals. Long-term monitoring showed, that in general, environmental parameters, such as temperature (6.5–11.6 °C), salinity (34.95–35.4) and current speed (average 8 cm s −1, peak current speed up to 38 cm s −1) largely resembled conditions previously recorded within North East Atlantic coral habitats. Major differences between site VK 826 and coral areas in the NE Atlantic were the much higher particle load, and the origin of the particulate matter. Several significant events occurred during the deployment period beginning with an increase in current speed followed by a gradual increase in temperature and salinity, followed by a rapid decrease in temperature and salinity. Simultaneously with the decrease in temperature and salinity, the direction of the current changed from west to east and cold and less turbid water was transported upslope. The most prominent event occurred in July, when a westward flow lasted over 21 days. These events are consistent with bottom boundary layer dynamics influenced by friction (bottom Ekman layer). The Mississippi River discharges large quantities of sediment and dominates sedimentation regimes in the area. Furthermore, the Mississippi River disperses large amounts of terrestrial organic matter and nutrients, resulting in increased primary productivity, whereby marine organic matter is produced that will sink to the seafloor and can serve as food for the cold-water corals and associated species. As a result mass fluxes from the sediment trap were higher (1120–4479 mg m −2 day −1) than those observed in the North East Atlantic and were highest during periods of westward-flow, which corresponded to warm turbid water. During eastward-flow, colder and less turbid water was pushed upsl