357
22.2 Hard-Bottom Communities: Deep-Sea Corals
and Associated Fauna
Although much less widespread than sediment environments (Glover and Smith
2003), hard grounds are essential in the deep sea as they provide substrate to foundation species such as deep-sea corals, creating hot spots of biodiversity. Unlike
their shallow-water counterparts, deepwater corals occur at all latitudes, commonly
between 200 and 1000 m, and down to 6000 m for some species (Grasshoff 1981;
Roberts et al. 2006; Watling et al. 2011). Because deepwater coral’s diet is based on
plankton or particles in suspension in the water column, they are usually found in
areas of pronounced topographic relief, where currents are strong enough to provide
them with food and prevent smothering by sediment (Bryan and Metaxas 2006;
Roberts et al. 2006).
Whether they form reefs, like the well-studied scleractinian Lophelia pertusa, or
dense aggregations, deep-sea corals enhance diversity by increasing the structural
complexity of the seafloor (Buhl-Mortensen and Mortensen 2005; Jensen and
Frederiksen 1992; Krieger and Wing 2002; Stone 2006). Numerous species use
deepwater corals as habitat, feeding ground, shelter from predators, or nursery,
resulting in coral ecosystems being associated with a higher diversity and abundance of megafaunal organism than the surrounding deep-sea environment (Baillon
et al. 2012; Buhl-Mortensen and Mortensen 2005; Etnoyer and Warrenchuk 2007;
Krieger and Wing 2002). If many studies have focused on characterizing the fauna
associated with deepwater corals, the nature of the relationship between corals and
their associates is still poorly understood (Buhl-Mortensen 2004). Of the approximately 1000 invertebrate species reported on deep-sea corals, about 100 have been
characterized as symbionts. The large majority of these symbionts were either
described as parasites or commensals, and only a few species appear to have a mutualistic relationship with corals (Buhl-Mortensen 2004; Girard et al. 2016).
The high biodiversity ecosystems sustained by deep-sea corals are also longlasting due to the high longevities generally recorded for deepwater corals. Several
species can live for hundreds of years, and the oldest coral colony recorded is over
4000 years old (Andrews et al. 2002; Prouty et al. 2016; Roark et al. 2006). However,
deep-sea corals often have slow growth and metabolic rates and are thus particularly
vulnerable to the ever-increasing number of anthropogenic threats (Andrews et al.
2002; Cordes et al. 2001; Prouty et al. 2016).
22.2.1 Hard-Bottoms Before DWH
The presence of deep-sea corals in the GoM has been known for decades (Moore and
Bullis 1960), but until more recently, few studies focused on these ecosystems. In
order to address this knowledge gap and evaluate the potential environmental impacts
from the oil and gas industry on hard-bottom communities, several multidisciplinary
22 Deep-Sea Benthic Faunal Impacts and Community Evolution Before, During…
22.2 Hard-Bottom Communities: Deep-Sea Corals
and Associated Fauna
Although much less widespread than sediment environments (Glover and Smith
2003), hard grounds are essential in the deep sea as they provide substrate to foundation species such as deep-sea corals, creating hot spots of biodiversity. Unlike
their shallow-water counterparts, deepwater corals occur at all latitudes, commonly
between 200 and 1000 m, and down to 6000 m for some species (Grasshoff 1981;
Roberts et al. 2006; Watling et al. 2011). Because deepwater coral’s diet is based on
plankton or particles in suspension in the water column, they are usually found in
areas of pronounced topographic relief, where currents are strong enough to provide
them with food and prevent smothering by sediment (Bryan and Metaxas 2006;
Roberts et al. 2006).
Whether they form reefs, like the well-studied scleractinian Lophelia pertusa, or
dense aggregations, deep-sea corals enhance diversity by increasing the structural
complexity of the seafloor (Buhl-Mortensen and Mortensen 2005; Jensen and
Frederiksen 1992; Krieger and Wing 2002; Stone 2006). Numerous species use
deepwater corals as habitat, feeding ground, shelter from predators, or nursery,
resulting in coral ecosystems being associated with a higher diversity and abundance of megafaunal organism than the surrounding deep-sea environment (Baillon
et al. 2012; Buhl-Mortensen and Mortensen 2005; Etnoyer and Warrenchuk 2007;
Krieger and Wing 2002). If many studies have focused on characterizing the fauna
associated with deepwater corals, the nature of the relationship between corals and
their associates is still poorly understood (Buhl-Mortensen 2004). Of the approximately 1000 invertebrate species reported on deep-sea corals, about 100 have been
characterized as symbionts. The large majority of these symbionts were either
described as parasites or commensals, and only a few species appear to have a mutualistic relationship with corals (Buhl-Mortensen 2004; Girard et al. 2016).
The high biodiversity ecosystems sustained by deep-sea corals are also longlasting due to the high longevities generally recorded for deepwater corals. Several
species can live for hundreds of years, and the oldest coral colony recorded is over
4000 years old (Andrews et al. 2002; Prouty et al. 2016; Roark et al. 2006). However,
deep-sea corals often have slow growth and metabolic rates and are thus particularly
vulnerable to the ever-increasing number of anthropogenic threats (Andrews et al.
2002; Cordes et al. 2001; Prouty et al. 2016).
22.2.1 Hard-Bottoms Before DWH
The presence of deep-sea corals in the GoM has been known for decades (Moore and
Bullis 1960), but until more recently, few studies focused on these ecosystems. In
order to address this knowledge gap and evaluate the potential environmental impacts
from the oil and gas industry on hard-bottom communities, several multidisciplinary
22 Deep-Sea Benthic Faunal Impacts and Community Evolution Before, During…