Importance

Sensitivity

Feasibility of management

The criteria for assessing the ‘importance’ of a species or community from a conservation-related perspective have 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 the ‘Sea pens and burrowing megafauna’ biotope complex. 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 are CMU.SpMeg.Fun and IMU.PhiVir, both of which are confined to a small number of Scottish sea lochs (IMU.PhiVir has one isolated example in Portland Harbour). The sea loch representatives are distributed along a large stretch of the western Scottish coastline, but their collective spatial extent must be fairly small.

Species falling within this category are the sea pen Funiculina quadrangularis, the anemones Pachycerianthus multiplicatus and Scolanthus callimorphus, and the brittlestar Asteronyx loveni. All of these species do occur outside British waters, so that their conservation importance must be defined in a British context. Some megafaunal burrowers (eg. Axius stirhynchus) are known from only a small number of records, but these animals are too easily overlooked to be classed with any confidence as truly rare.

None of the biotopes or species considered here are known to be currently declining. Existing records are inadequate to determine whether any declines have occurred in the recent past.

Biotopes with sea pens and megafauna have certainly been best-characterized and studied in British waters, but as discussed in Chapter II, similar biological communities are known from sedimentary habitats in many parts of the world. The anemone Pachycerianthus multiplicatus is known only from Scotland, Ireland and Scandinavia, so that British waters might conceivably hold a significant proportion of its total population.

British and Irish waters do support good examples of the biotopes in question, with a high diversity of burrowing megafauna and several sea pen species. Their perceived importance may change as information is gained from other regions, but at present the British representatives are probably the best-known examples of their type.

The various small invertebrates found as commensals in megafaunal burrows are also found as members of the general sediment fauna rather than being specialized burrow associates. The one example known in this category is the brittlestar Asteronyx loveni, which appears to be an obligate commensal of large anthozoans such as Funiculina quadrangularis.

Marine sediments do support a large number of invertebrate species, especially if the entire size range of animals is considered. Biotopes characterized by sea pens and burrowing megafauna are not known to be unusually species-rich, but have not been compared systematically with sediments lacking this component of the fauna. It is possible that the patchwork of disturbance created by megafaunal burrowers may promote a higher local species diversity (of macro- and meiofauna) than would otherwise exist.

Marine sediments are certainly important in the geochemical cycling of carbon, nutrients and metals in coastal environments. Bioturbation is known to affect geochemical processes but no studies have yet been able to assess its importance at the ecosystem level (ie. comparing the efficiency of cycling through bioturbated and non-bioturbated sediments).

The biotope complex does not possess any features within this category.

This assessment leads to the overall conclusion that the conservation importance of the ‘Sea pens and burrowing megafauna’ biotope complex lies in:

• The restricted distribution and spatial extent of the biotopes and species listed under (a) above.
• The fact that the British representatives are particularly good examples of their type.

As discussed in Chapters V and VI, the biotopes within this complex (including CMU.SpMeg.Fun and IMU.PhiVir, defined above as being of conservation importance) are sensitive to disturbance by trawling and organic pollution, and probably by chemical contamination of various kinds. The ability of these biotopes to recover after disturbance (ie. return to their original state) is not well-understood. Sediment macrofaunal communities can recover following the cessation of organic enrichment, although the time required for this to occur is strongly dependent on local conditions (Pereira, 1997). The life cycles of some animal species may act as a barrier to recolonization following local disappearance. This will be true especially of species with low reproductive rates, and short-lived larvae with low dispersal abilities (Hiscock, submitted). Species with a sessile or sedentary lifestyle as adults will clearly also be unable to recolonize an area other than by larval dispersal.

The life cycles of most of the characteristic species of this biotope complex are poorly-known, but the studies reviewed in Chapter IV suggest that taxa with poor colonization ability will include the three sea pens, Pachycerianthus multiplicatus, Calocaris macandreae and possibly Maxmuelleria lankesteri. Local extinction might not be easily (or ever) reversed in these species, a feature of particular importance to those with fragmented distributions (eg. Funiculina, Pachycerianthus).

The biotopes and species defined above as being of conservation importance are limited in their distribution within the UK to semi-enclosed water bodies of relatively small spatial extent (sea lochs, Portland Harbour). In these circumstances, effective habitat management to promote their survival is a feasible proposition. This would involve monitoring of, and possibly regulation of, those human activities likely to damage the species and communities of interest, namely the use of mobile fishing gear and the discharge of organic material into the sea.

Examples of the ‘Sea pens and burrowing megafauna’ biotope complex existing in open sea areas (Clyde, Irish Sea, Minches, North Sea) may also be subject to management, but any measures taken (eg. closure of areas to trawling) will come within the context of fishery regulation, these areas being the major commercial Nephrops grounds.

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