Threats to Coral

Cold-water coral habitats are becoming increasingly pressurised by the activities of humans. Interest in the deep ocean is growing as it becomes a valuable point of exploitation for biological and mineral resources (Freiwald et al. 2004). There are numerous different types of threats to these habitats but are all induced by anthropogenic activity:
 1) Bottom Trawling
2) Pollution and waste disposal
3) Cable and Pipeline positioning
4) Mineral exploitation
5) Destructive scientific sampling
6) Coral exploitation trade
7) Increased atmospheric carbon dioxide
(Friewald et al. 2004) 

The three threats of most concern at present are: Bottom trawling, Hydrocarbon exploitation and increased atmospheric carbon dioxide. 

Bottom Trawling
Currently around 3.5 million fishing vessels are in use and as a result very there are few areas of the ocean which remain unexploited.  At present 47% of the worlds main stocks are fully exploited and 18% are over exploited (Jennings et al. 2001). Most shelf seas are fished to depths of 200 metres, but with the depletion of shallow water fish stocks fishing pressures have turned to the deep to exploit different species such as the Orange Roughy (Hoploslethus atlantious) and Redfish (Sebastes spp) (Rogers 2004).
Bottom trawlers are mobile fishing gear towed behind a vessel with weighted chains to ensure constant contact with the seabed (Figure 11). They are made to dredge over rough terrain and so can trawl straight over coral reefs; several tonnes of chain smashes the coral framework into pieces (Rogers 2004). Slow growth rate and high longevity make these habitats vulnerable to the effects of over-fishing. Research suggests that in areas where intense trawling has occurred the colony has been reduced in size so greatly that reproduction is no longer viable. In these cases regeneration of reefs is unlikely and the remains are often grazed by sea urchins (Rogers 2004).  In Norwegian waters 50% of Lophelia reefs have already been destroyed as a result of trawling, the Tasman Sea mount is just another of many examples of heavily damaged environments. Destruction of deep water coral reefs could explain why the depletion of certain fish stocks have not yet recovered (Rogers 2004). 

Figure 11: Drawing showing impact the a bottom trawl can have on seabed (Freiwald et al. 2004)

Follow this link to see the distruction bottom trawling has had on a Norwegian coral reef and the extreme danger these habitats are facing . (Video 3)

 Mineral Exploitation / Pipe and Cable Positioning
Exploitation of hydrocarbons takes places in the North Sea, Norwegian Shelf, NW Scotland, Mauritania, Campos Basin and SE Brazil (Freiwald et al. 2004). The physical impact of placing oil platforms, pipelines and drilling disturbs the coral habitat. Discharges of rock cuttings can cause an increase in sedimentation which can smother poypls and decrease growth (Roberts et al. 2006).
Cables and pipe lines are positioned for telecommunication, gas and electricity, fishing activities have resulted in moving these deeper (1500m) to avoid accidental trawling. There has not been examples of this activity disturbing coral reefs but there is a need for further investigation into its effects (Freiwald et al. 2004).
Oil companies are now required to conduct environmental assessments before drilling; this is a small step in ensuring the protection of cold water coral reefs (Freiwald et al. 2004). 

Increased Atmospheric Carbon Dioxide
There is a general consensus that atmospheric carbon dioxide is increasing at an exponential rate, it is causing the greatest increase in ocean acidification in the last 300 million years (Roberts et al. 2006). The IPCC predicts a 30% decrease in saturation of calcium carbonate, this will result in lower alkalinity (Kleypas et al. 1999). The effects of this on cold-water corals has not yet been investigated but it can be assumed that a decrease in saturation is not good for a calcium carbonate driven ecosystem (Roberts et al. 2006). In tropical coral reefs it has been estimated that calcification with reduce by 54% if atmospheric carbon dioxide doubles; in this environment corals wills struggle to produce skeletal structures (Roberts et al. 2006).

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