Review of Cabling Techniques and Environmental Effects Applicable
Review of Cabling Techniques and Environmental Effects Applicable
Review of Cabling Techniques and Environmental Effects Applicable
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Potential impacts <strong>and</strong> mitigration measures<br />
disturbed sites took nearly twice as long. Nevertheless, the higher intensity<br />
disturbance did not have a significantly greater effect on the community than<br />
was found in the less intense disturbance (Dernie et al., 2003). This implies that<br />
cabling could take longer still for recovery due to the depths <strong>of</strong> disturbance.<br />
However, cabling activity replaces the sediment, albeit in a different structure,<br />
<strong>and</strong> the majority <strong>of</strong> the communities are within the top 10-20cm <strong>of</strong> the sediment<br />
indicating that recovery may be influenced strongly when disturbance intensity<br />
changes between these depths but may not differ too much once disturbance<br />
occurs below this depth.<br />
Studies have been undertaken in a number <strong>of</strong> habitat types in order to record<br />
recolonisation rates following dredging activity. The results <strong>of</strong> these studies<br />
are summarised in Newell et al., 1998, <strong>and</strong> show variation in recovery times <strong>of</strong><br />
between 3 weeks for freshwater semi liquid mud <strong>and</strong> 12 years (<strong>and</strong> >7 years)<br />
for s<strong>and</strong>-gravels (<strong>and</strong> coral reefs). Studies have shown that adult migration has<br />
been observed as the major mode <strong>of</strong> recolonisation (Savidge & Taghon, 1988;<br />
Thrush et al., 1991). These recovery rates should however be put in context with<br />
the nature <strong>and</strong> extent <strong>of</strong> the disturbance compared to cable installation. Due to<br />
the localised nature <strong>of</strong> the cabling activity whereby the area affected is generally<br />
restricted to 2-3m width <strong>of</strong> substrate, the overall effect on the benthic ecology is<br />
not likely to be significant if the habitat distribution throughout the wider area<br />
is homogenous. However, if there are specific areas, directly in the path <strong>of</strong> the<br />
cable, where the habitats are not widely distributed <strong>and</strong>/or particularly sensitive<br />
to disturbance, then these will need to be avoided. One such example includes<br />
cable installation through areas <strong>of</strong> biogenic reef comprising <strong>of</strong> Sabellaria<br />
spinulosa, the reef building honeycomb worm. The reefs formed by the worm<br />
provide valuable habitat for many associated species <strong>and</strong> would be destroyed<br />
by cabling activity, albeit in very localised areas. They are also listed as a priority<br />
habitat under the EU Habitats Directive <strong>and</strong> specialised surveys are required<br />
in order to define the boundaries <strong>of</strong> the reef. Although these species have a<br />
high recoverability, their nature conservation importance means that any direct<br />
loss that damages the integrity <strong>of</strong> the reef structures or adversely affects their<br />
development would be considered as being <strong>of</strong> significance.<br />
In summary, potential effects from disturbance on seabed habitats are as<br />
follows:<br />
Rock – some scarring may occur dependent on the rock type e.g. effects on s<strong>of</strong>t<br />
rock such as s<strong>and</strong>stone habitats will be more significant. Encrusting <strong>and</strong> attached<br />
fauna <strong>and</strong> flora can be dislodged/disturbed. Species inhabiting rock habitats are<br />
<strong>of</strong>ten sessile species <strong>and</strong> are therefore more susceptible to disturbance.<br />
Chalk – a permanent scar is likely. Cable burial techniques will disturb epifauna/<br />
flora inhabiting chalk habitat. Disturbance <strong>of</strong> chalk will cause a high visibility<br />
plume which will remain in suspension for long periods <strong>of</strong> time, but which is<br />
unlikely to cause more than an aesthetic effect.<br />
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