Coral Reef NOAA
 
November 28, 2014  

Threats to Deep-Sea Corals



Overview of Threats to Deep-Sea Corals
Specific Threats
   Bottom Trawling and Other Bottom-tending Fishing Gear Impacts
   Energy and Mineral Exploration and Development
   Climate Change and Ocean Acidification
Other Threats

underwater image of two divers being pulled on towboards to survey a reef
underwater image looking up at a towboard diver from below
The top Oculina coral reef is undisturbed. Trawling has devastated the one below, located at Oculina Banks off the coast of Florida. Only about 10 percent of Oculina habitat remains intact. Photo Credits: Top: R.G. Gilmore; Bottom: NURC/UNCW

Overview of Threats to Deep-Sea Corals

Structure-forming deep-sea corals are generally slow-growing and fragile, making them and their associated communities vulnerable to human-induced impacts, particularly physical disturbance. With the exception of a few areas (e.g., the Oculina Banks), the extent of habitat degradation as a result of anthropogenic impacts is largely unknown. Activities that can directly impact deep-sea coral communities include fishing using bottom-tending fishing gear, deep-sea coral harvesting, fossil fuel and mineral exploration and extraction, and submarine cable/pipeline deployment. Invasive species, climate change and ocean acidification represent additional serious threats.

top

Specific Threats

Bottom Trawling and Other Bottom-tending Fishing Gear Impacts

Disturbances to deep-sea coral ecosystems from bottom-tending fishing gear, especially bottom trawl gear, have been well documented where they have been studied in U.S. waters and in other regions around the world. Bottom trawling is widespread and considered the major threat to deep-sea corals in most U.S. regions where such fishing is allowed and overlaps with areas where deep-sea corals are present. The area of seafloor contacted by bottom trawls is relatively large, the force against the seafloor from the trawl gear is substantial, and the spatial distribution of bottom trawling is extensive. Although not as destructive as bottom trawls and dredges, other types of fishing gear can also have detrimental effects on deep-sea corals. Bottom-set gillnets, bottom-set longlines, pots and traps all impact the seafloor. Vertical hook and line fishing, used in both recreational and commercial fishing, has the potential for some damage to fragile corals by the weights used, but such damage is minimal compared to other bottom-tending gear. [a,b]

Energy and Mineral Exploration and Development

Exploration for and production of oil and gas resources can impact deep-sea coral communities in a variety of ways. Potential threats include the physical impact of drilling, placement of structures on the seafloor (e.g., platforms, anchors, pipelines, or cables), discharges from rock-cutting during the drilling process, and intentional or accidental well discharges or release of drilling fluids. Smothering and death of corals by drilling muds and cuttings was observed on Lophelia pertusa colonies living on an oil platform in the North Sea close to drilling discharge points. [c] The use of anchors, pipelines, and cables for oil exploration/extraction can be destructive to sensitive benthic habitats as well. While deployment of oil and gas pipelines can cause localized physical damage to deep-sea corals. The use of anchors, pipelines, and cables for oil exploration/extraction can be destructive to sensitive benthic habitats as well.

Climate Change and Ocean Acidification

The potential impacts of climate change on deep-sea coral ecosystems are unknown, however, the associated threat of ocean acidification is a significant concern. Since pre-industrial times, over half of the additional CO2 attributed to human activities released in the atmosphere has been absorbed by the ocean. Once in the ocean, CO2 lowers the saturation of the minerals (principally calcium carbonate) used to form skeletal structures in many major groups of marine organisms, including corals. The saturation level of calcium carbonate decreases with depth, and therefore the effect of ocean acidification on deep-sea corals could be significant. Projected increases in ocean acidity could result in severe ecological changes for deep-sea corals, and may influence the marine food chain from carbonate-based phytoplankton up to higher trophic levels. [d]

top

screenshot from the OA NODE Module.  The screenshot includes a graph, a box where users can select OA parameters to change, and a box that shows an animation of what those parameters will do to a reef over time.
Red coral necklaces fill a store display window. Harvesting deep-sea coral to produce jewelry like this threatens these ecosystems. Photo credit: Devin Harvey/Marine Photobank

Other Threats

Other activities that can adversely impact deep-sea corals and the communities that depend on them include coral harvesting; marine debris; and submarine cable/pipeline deployment; and invasive species.

top

Citations:

top


screenshot from the OA NODE Module.  The screenshot includes a graph, a box where users can select OA parameters to change, and a box that shows an animation of what those parameters will do to a reef over time.