Sensitivity to human activities
Maerl beds in subtidal waters have been utilised over a long period. An early reference
to maerl beds in Britain was made by Ray (1690, cited by Irvine & Chamberlain, 1994) "Corallium album pumilum nostras. Small
white coral. .... It is found plentifully in the ouze dredged out of Falmouth Haven to
manure their lands in Cornwal". In France
also, maerl has been used as a soil fertilizer for several centuries (Cabioch, 1969).
Maerl is extracted in large amounts for use in animal food additives, water filtration
systems, etc, but mostly to replace lime as an agricultural soil conditioner. It is
occasionally used for miscellaneous other purposes such as hardcore for filling roads, and
surfacing garden paths. Maerl can also be used for soil improvement in horticulture. Maerl
extraction forms a major part of the French seaweed industry, both in terms of tonnage and
value of harvest (Briand, 1991). There are conflicting reports on the benefits of maerl
use as opposed to the use of dolomite or calcium carbonate limestone (Blunden et al.,
1997). As a result of the commercial interest in maerl beds, most research work has been
based on the three main areas of commercial exploitation, namely Brittany, Cornwall and
the west of Ireland.
In addition to the obvious direct effects on maerl of harvesting, other direct and
indirect effects on maerl beds have also been noted. Damage to the surface of the beds is
caused by heavy demersal fishing gear. Permanent moorings for pleasure boats can have
similar, more localized, effects, due to the effects of mooring chains being dragged in
circles on the maerl, particular at low tide. The changes in farming practices this
century have resulted in increased turbidity in coastal waters both from silt loads and
from nutrient run-off. However, there is very little evidence supporting claims that these
factors are damaging to maerl beds.
There is little doubt that many human activities can and will result in damage to maerl
biotopes but there is an urgent need for continued and rigorous scientific study to better
link human activities and impacts on these biotopes, especially beyond localised areas,
looking at communities and beds as a whole. In addition, in cases where an alternative
resource can be found, e.g. using lime as a soil condition instead of maerl, use of the
alternative material should be required, and justified by the real economic costs of
large-scale habitat loss.
Several types of human impact on maerl beds are being studied by the BIOMAERL
programme. Anthropogenically impacted maerl beds are paired with relatively pristine
control grounds. The impacts are from the use of towed demersal fishing gears; culture of
the edible mussel; eutrophication; and maerl extraction.