Biodiversity, Conservation Importance and Sensitivity of the Biotope
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:
Rare or very restricted in distribution
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.
In decline or have been
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
A high proportion of the regional or world population or extent
The UK and Ireland are undoubtedly areas of global importance for
shallow-water epifaunal brittlestar beds, a relatively rare biotope on a world scale
Particularly good or extensive examples of their type
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.
Keystone species providing a habitat for other species
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.
Biotopes with a particularly high species richness
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.
Biotopes important for the efficient functioning of regional ecosystems
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.
Of high aesthetic, symbolic or recreational importance
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.
Feasibility of management
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.