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.

Direct impacts                     References

Indirect effects