Importance

Sensitivity

Feasibility of management

The criteria for assessing the ‘importance’ of a species or community from a conservation-related perspective have the been the subject of much debate. They are perhaps especially difficult to establish in the marine environment, where basic knowledge of distributions, life cycles and ecological functioning is still at a low level compared with the terrestrial situation. A number of criteria (not necessarily exhaustive) for assessing conservation importance are listed below, with details of their relevance to brittlestar beds. Criteria include those listed by Hiscock (submitted).

Habitats, communities or species may be considered ‘important’ from a conservation - related perspective if they are:

Of the MNCR-defined biotopes included within this complex, the most restricted is the Ophiopholis-dominated variant MCR.Oph.Oacu, which is found at a small number of sites in Scotland and Ireland. Ophiopholis aculeata itself is more widespread and cannot be considered a rare species. There are no other rare species known from these biotopes.

Brittlestar beds as a whole are not known to be currently declining. Fluctuations have been recorded in the past, but these appear to be cyclical, and purely natural events.

The UK and Ireland are undoubtedly areas of global importance for shallow-water epifaunal brittlestar beds, a relatively rare biotope on a world scale (Aronson, 1989).

The frequency and extent of brittlestar beds around the British Isles, compared with their relative rarity in other parts of the world, means that they can be considered the ‘classic’ examples of their type.

Brittlestars are clearly the ‘keystone’ species of these biotopes, but this is true only in a trivial sense, given that the biotopes themselves are specifically defined on the basis of mass brittlestar occurrence. The beds do provide a habitat for other species, but none are known to be unique to this community.

Beds on sedimentary substrata may support a higher density and species richness of infauna than nearby brittlestar-free substrata, but this is probably not a feature of major conservation importance. The unique and important features of brittlestar beds relate to the brittlestars themselves rather than the associated fauna.

There are indications that brittlestar beds may be important components of the carbon and nutrient cycles in their local ecosystems, but there are not yet sufficient data to evaluate this role fully.

Brittlestar beds do not possess any features within this category.

This assessment leads to the overall conclusion that the conservation importance of subtidal brittlestar beds lies in:

• The restricted distribution of the biotope MCR.Oph.Oacu
• The British Isles contain a large proportion of the known shallow-water epifaunal brittlestar beds, and these are the best-known examples of their type.
• Large beds may be locally important elements in ecosystem functioning.

The scientific importance of brittlestar beds and their potential usefulness as biological indicators have been discussed in Chapters I and VIII.

The cyclical fluctuations in the extent of beds in the western Channel, and the mass mortality of brittlestars in the Gulf of Trieste show that these aggregations are sensitive to environmental changes at a range of scales. Sensitivity to pollutants such as oil, pesticides or heavy organic enrichment has not been demonstrated in the field but can be considered likely.

It is unlikely that active steps could be taken to manage brittlestar beds in large, open-coast areas such as the western English Channel, other than through generic measures designed to maintain the overall quality of the marine environment. In geographically more restricted areas such as sea lochs, local controls could be considered on activities such as the use of anti-parasite chemicals in fish farms, if these were specifically shown to be affecting brittlestar beds or other benthic biotopes.

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