Moorings

Fishing

Collection by Divers

Organic Enrichment

Regeneration Potential

There are a number of activities which are known to damage, or have the potential to damage Serpula reefs, the majority of these are mentioned in Moore (1996) on which the summary below is largely based.

Scale is an important consideration. The reefs are small and extremely limited in distribution so that damage which might be considered modest in another community could be regarded as serious in the case of serpulid reefs.

The reefs are clearly fragile enough to be very easily damaged by physical impingement. Severe damage, albeit on a very local scale, caused by movement of mooring blocks and chains has been seen in parts of Loch Creran. One mooring had reduced colonies to rubble within a radius of about 10 m, while further extensive damage was caused within about 50 m of salmon cages. Although many worms survive such damage, the integrity of the habitat, and its value to other species, is grossly reduced. In Loch Creran, limiting moorings to areas with a depth greater that about 15 m, together with careful choice of ground tackle and limited length of riser chain to reduce movement would minimise or avoid damage.

Fishing is an activity which could potentially be very damaging. Moore (1996) reported that at the time of his study fishing was limited to occasional Nephrops trawling, which was of low risk as it occurred in deeper, muddier areas where serpulid reefs were not found, and there was no evidence from extensive dive surveys of damage that appeared to be caused by bottom fishing. Dredging/trawling for queen scallops, of which stocks seems to be present in Loch Creran, had not been observed but has taken place since, at least in upper Loch Creran (Donnan, pers. comm.). There is clearly potential for damage to reefs although though there is no present knowledge of the extent of damage, if any, to date. Moore reports that reef areas often contain reasonable stocks of queen scallops. More detailed information on the overall distribution of queens, so that the proportion of the stock found inside and outside reef areas, would help in the preparation of a management strategy for fishing. It is strongly recommended that, if possible, fishing with potentially damaging gear such as dredges or trawls is prevented in areas of dense reefs.

Moore (1996) has pointed out that physical removal by divers, particularly for commercial aquaria, already occurs in Loch Creran. It is likely that this could be easily sustainable on a small scale, as seems to occur at present, but even rough estimates of the maximum sustainable rate of removal are not presently possible, making predictions of the effects of increased collection difficult.

Around 1 km of the south side of Loch Creran around the dump site for an alginate factory (at Barcaldine) was found to be totally devoid of reefs. However, conditions are likely to have been quite severe in the locality, since the discharge consisted of thousands of tonnes per annum of organically rich de-alginated seaweed residue deposited into a poorly flushed loch, and a thick bacterial mat was observed on the seabed within this area (Moore, 1996). It does not therefore follow that this absence of reefs indicates any special sensitivity to organic pollution. If detailed historical information on water quality in the area is available through either the owners of the factory (Kelco Nutrasweet) or the appropriate authority, and or studies of the distribution of other marine organisms in the same area, a better assessment of its likely sensitivity could be made.

Since the discharge of seaweed residue ceased in October 1996 (Richard Searle, Kelco Nutrasweet, pers. comm.), this represents an ideal opportunity to study the rate of recolonisation of the area (see chapter VII) on which there is currently little information.

Artificial methods of regenerating reefs in areas where they have been lost have also not been studied, although an opportunity clearly exists in the area around Barcaldine. There is evidence that successful methods might be relatively easily devised for those areas where there is still already a viable population to provide larvae; dense aggregations of Serpula quickly cover many artificial surfaces left in Loch Creran, and ‘mini reefs’ up to around 15 cm in height can appear within three months or so (Moore, pers. comm.). Bosence (1979) successfully moved small pieces of reef to new areas within Ardbear Lough, with no apparent mortalities after a month or so, so long as the new area was not within the anoxic deeper parts of the Lough, but longer term monitoring of these transplants was not carried out. There thus seems to be potential for enhancement of reef areas by placement of suitable substratum in areas known to have good recruitment, with subsequent transfer to other areas if necessary, but this potential is as yet unproven.

In areas where there is no longer a viable population to provide larvae, as may now be the situation in Loch Sween, reefs will clearly not regenerate naturally. Unfortunately, given the apparent requirements for dense larval supply, as encouraged by low turnover of water, it currently seems likely that regeneration by artificial means such as transfer of young established colonies from other areas, while perhaps technically feasible, would need to be carried out on a scale which would be impractical in reality. Further information on growth and recruitment processes is needed to clarify this issue.

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