358
studies funded by the Bureau of Ocean Energy Management (BOEM) and the
National Oceanic and Atmospheric Administration (NOAA) were conducted after
2007 (Boland et al. 2017). These studies significantly contributed to improving our
knowledge of the biology and distribution of deepwater corals in the GoM.
Deep-sea corals occur throughout the GoM. In the deep GoM, they usually grow
on authigenic carbonates that formed as a by-product of the microbial alteration of
hydrocarbons coupled with anaerobic methane oxidation in the subsurface sediment
at seeps (Cordes 2009). Newly formed seeps are generally characterized by the
presence of microbial mats and rare megafauna. The precipitation of carbonates
resulting from microbial activity eventually provides hard substrate to foundation
species such as symbiont-containing vestimentiferan tubeworms and bathymodiolus mussels (Fisher et al. 2007). As seepage slows down, carbonates that are exposed
due to the erosion of the surrounding sediment can be colonized by deepwater corals. Deep-sea corals have also been observed growing on man-made structures such
as shipwrecks or oil platforms (Brooks et al. 2012; Larcom et al. 2014).
A total of 258 deep-sea coral species, predominantly octocorals (137 species)
and hexacorals (84 scleractinian and 28 antipatharian species), have been documented in the northern GoM (Etnoyer and Cairns 2016). Species distribution is
mostly dependent on depth. The reef-forming Lophelia pertusa is the most common
coral species on the upper continental slope and also the most extensively studied
(Cordes et al. 2008; CSA International 2007; Lessard-Pilon et al. 2010). Octocorals
cover a greater depth range, down to at least 3000 m, with species assemblages
being structured by depth (Quattrini et al. 2013).
As in the rest of the world, deep-sea corals enhance biodiversity in the deep
GoM. For instance, studies show that L. pertusa reefs in the GoM are associated
with diverse communities of associated fauna and that these communities are unique
and differ from communities associated with vestimentiferan tubeworms aggregations, even when in close proximity (Cordes et al. 2008; Lessard-Pilon et al. 2010).
Although the communities associated with octocorals in the GoM are less known,
numerous species including ophiuroids have been observed in association with
octocorals, and the documented presence of egg cases of a species of scyliorhinid
catshark on the octocoral Callogorgia delta indicates their importance as nursery
habitat (Etnoyer and Warrenchuk 2007; Girard et al. 2016).
22.2.2 Hard-Bottoms During DWH (2010)
To investigate potential impacts from the DWH oil spill on deep-sea corals, nine
known coral sites were explored between 15 October and 1 November (3 months
after the well was capped) during a Natural Resource Damage Assessment (NRDA)
expedition funded by BOEM and NOAA. All these sites were located more than
20 km from the well between 290 m and 2600 m depth, and no visible evidence of
impact was detected on coral communities there. However, a visibly impacted coral
community was discovered on 2 November in lease block Mississippi Canyon (MC)
P. A. Montagna and F. Girard
studies funded by the Bureau of Ocean Energy Management (BOEM) and the
National Oceanic and Atmospheric Administration (NOAA) were conducted after
2007 (Boland et al. 2017). These studies significantly contributed to improving our
knowledge of the biology and distribution of deepwater corals in the GoM.
Deep-sea corals occur throughout the GoM. In the deep GoM, they usually grow
on authigenic carbonates that formed as a by-product of the microbial alteration of
hydrocarbons coupled with anaerobic methane oxidation in the subsurface sediment
at seeps (Cordes 2009). Newly formed seeps are generally characterized by the
presence of microbial mats and rare megafauna. The precipitation of carbonates
resulting from microbial activity eventually provides hard substrate to foundation
species such as symbiont-containing vestimentiferan tubeworms and bathymodiolus mussels (Fisher et al. 2007). As seepage slows down, carbonates that are exposed
due to the erosion of the surrounding sediment can be colonized by deepwater corals. Deep-sea corals have also been observed growing on man-made structures such
as shipwrecks or oil platforms (Brooks et al. 2012; Larcom et al. 2014).
A total of 258 deep-sea coral species, predominantly octocorals (137 species)
and hexacorals (84 scleractinian and 28 antipatharian species), have been documented in the northern GoM (Etnoyer and Cairns 2016). Species distribution is
mostly dependent on depth. The reef-forming Lophelia pertusa is the most common
coral species on the upper continental slope and also the most extensively studied
(Cordes et al. 2008; CSA International 2007; Lessard-Pilon et al. 2010). Octocorals
cover a greater depth range, down to at least 3000 m, with species assemblages
being structured by depth (Quattrini et al. 2013).
As in the rest of the world, deep-sea corals enhance biodiversity in the deep
GoM. For instance, studies show that L. pertusa reefs in the GoM are associated
with diverse communities of associated fauna and that these communities are unique
and differ from communities associated with vestimentiferan tubeworms aggregations, even when in close proximity (Cordes et al. 2008; Lessard-Pilon et al. 2010).
Although the communities associated with octocorals in the GoM are less known,
numerous species including ophiuroids have been observed in association with
octocorals, and the documented presence of egg cases of a species of scyliorhinid
catshark on the octocoral Callogorgia delta indicates their importance as nursery
habitat (Etnoyer and Warrenchuk 2007; Girard et al. 2016).
22.2.2 Hard-Bottoms During DWH (2010)
To investigate potential impacts from the DWH oil spill on deep-sea corals, nine
known coral sites were explored between 15 October and 1 November (3 months
after the well was capped) during a Natural Resource Damage Assessment (NRDA)
expedition funded by BOEM and NOAA. All these sites were located more than
20 km from the well between 290 m and 2600 m depth, and no visible evidence of
impact was detected on coral communities there. However, a visibly impacted coral
community was discovered on 2 November in lease block Mississippi Canyon (MC)
P. A. Montagna and F. Girard