Recent findings of typically deep-dwelling corals in these habitats shed new light on the
persistence of corals in deep waters (Roder et al., 2013; Qurban et al., 2014). Although
none of the coral species found in the Red Sea are among the most common globally
(see above for list), limited framework growth is recorded mainly by Eguchipsammia
fistula under food- and oxygen deprived conditions (1.02 – 2.04 ml l
-1
). Coral survival
under such extreme environmental conditions may follow the strategy of metabolic
depression (sensu Guppy and Withers, 1999), including depressed aerobic respiration
and calcification rates. However, the high temperatures in combination with high
aragonite saturation values of 3.44-3.61 in the Red Sea may facilitate calcification under
these otherwise adverse conditions (Roder et al., 2013). The cold-water coral
communities in the northern Gulf of Mexico belong to the most intensively studied sites
in waters of the United States (e.g., Cordes et al., 2008). The major framework-
constructor is L. pertusa and most environmental variables (i.e., temperature, salinity
and aragonite saturation state) reflect the ranges known from Atlantic Lophelia sites
(Davies et al., 2010; Lunden et al., 2013). However, dissolved oxygen values appear to
be low, 2.7–2.8 ml l
−1
are typically observed (Davies et al., 2010) and values as low as 1.5
ml l
−1
have been recorded adjacent to coral mounds (Georgian et al., 2014). Coral
nubbins from these Gulf of Mexico populations survived and grew in the lab at oxygen
levels as low as 2.9 ml l
-1
, but eight-day incubations at lower oxygen concentrations (1.5
ml l
-1
) caused complete mortality, suggesting that these conditions are short-lived in situ
(Lunden et al., 2014). Similarly, low oxygenation levels were found in the newly
discovered Lophelia-Enallopsammia coral mounds in the Campeche Bank coral mound
province, in the southern Gulf of Mexico (Hebbeln et al., 2014). It is possible that the
low oxygen concentrations of the Gulf of Mexico result in lower growth rates observed
for L. pertusa on natural (Brooke and Young, 2009) and man-made substrata (Larcom et
al., 2014), although this remains to be examined empirically.
There have been numerous recent advances in our knowledge of the oceanographic
variables describing coral habitat in the deep sea. However, knowledge gaps still remain
when up-scaling from local to regional to global scales. Furthermore, limited capacity to
carry out long-term in situ measurements with benthic landers and cabled observatories
persists. This knowledge is of utmost importance to understand the consequences of
already perceptible environmental change, such as ocean acidification, spread of oxygen
minimum zones, and rising temperatures, on deep-sea ecosystems.
3.
Major Pressures Linked to the Trends
Numerous anthropogenic threats to cold-water coral communities exist, the most
significant of which include fisheries, hydrocarbon exploration and extraction, and
mining, as well as global ocean change including warming and acidification. An improved
understanding of the function of cold-water corals as habitat, feeding grounds and
nurseries for many fishes including certain deep-sea fisheries targets has emerged along
with concerns as to the impact of fisheries on these ecosystems (Costello et al., 2005;
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Grehan et al., 2005; Stone, 2006; Hourigan, 2009; Maynou and Cartes, 2012). Physical
impacts from both trawl fisheries and long-lining, now being conducted as deep as
1500-2000 m, are likely to be significant anywhere deep-water fisheries are active, but
have been well-demonstrated in the North Atlantic and Norwegian Seas (Roberts et al.,
2000; Fossa et al., 2002; Hall-Spencer et al., 2002, Reed, 2002), on the Australian
seamounts (Koslow et al., 2001), off the coast of New Zealand (Probert et al., 1997,
Clark and Rowden, 2009), and Southwestern Atlantic slope (Kitahara, 2009). Trawl
fisheries have the most severe impacts, by removal of large volumes of organisms and
of cold-water coral framework from the seafloor and the concomitant destruction of the
habitat, but long-lining impacts have also been observed (Heifetz et al., 2009). Recovery
times from these types of disturbance are likely to require settlement and regrowth of
the corals, which based on radiometric dating of cold-water coral species, can require
decades to centuries (Andrews et al., 2002; Prouty et al., 2014) or in the case of the
black corals, could require millennia (Roark et al., 2009). Direct evidence of recovery
times is consistent with these estimates, indicating that there was no apparent recovery
5-10 years after the closure of seamount fisheries on the Tasmanian seamounts (Althaus
et al., 2009). These impacts have also been the most recognized in terms of
management efforts, thus far (see below).
Installation of oil and gas offshore facilities and drilling activities (see Chapter 21) have a
great potential to impact cold-water coral communities. The potential impact should be
higher in areas where much of the available substrate is from authigenic carbonates
related to natural oil and gas seepage, such as the Gulf of Mexico (Cordes et al., 2008),
some locations on the Norwegian margin (Hovland, 2005), and the New Zealand margin
(Baco et al., 2010). Most of the typical impacts would be from infrastructure installation
and the deposition of drill tailings that can include high concentrations in barium,
among other potential toxins (Continental Shelf Associates, 2006). These impacts are
typically confined to a few hundred metres, but can have been shown to extend over 2
kilometres in some cases (Continental Shelf Associates, 2006). The most glaring example
of oil and gas industry impacts in the deep sea is the Deepwater Horizon disaster in 2010
in the Gulf of Mexico. Material conclusively linked to the spill was discovered on
octocoral colonies (primarily Paramuricea biscaya) approximately 11 km away from the
site of the drilling rig (White et al., 2012a). These colonies suffered tissue loss and many
have continued to decline in health since the spill (Hsing et al., 2013). Subsequent
surveys detected at least two additional sites, extending the impacts to 26 km from the
site of the well, and from 1,370 m to 1,950 m water depth (Fisher et al., 2014). One of
the primary lessons learned from this tragic incident is that there is an urgent need for
improved baseline surveys in deep waters prior to industrial activity. Offshore energy
industry activity in the form of wind and wave energy is also increasing (see Chapter 22),
and physical structure placed on the seafloor, including pipelines and cables, could have
an impact on cold-water corals if the appropriate surveys are not completed prior to
installation.
Mining activities have increased in the deep sea in recent years. This activity has mainly
focused on massive seafloor sulphide deposits near hydrothermal vents, cobalt-rich
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