1. The distribution and abundance of reefs of Serpula 6ermicularis was examined in Loch Creran, the only known remaining site of reefs of this species in Scotland. In view of the decline in populations elsewhere, the aims included assessment of the importance of the Scottish population in terms of conservation of the reef habitat and the establishment of a baseline against which future changes could be gauged. A further objective was to determine appropriate conservation management of the reefs by examining the influence of both natural and anthropogenic factors.2. Reefs were largely restricted to a depth range of 1 -13 m. Factors controlling the depth distribution are discussed.3. Serpula 6ermicularis reefs colonized a variety of substrata, but predominantly grew on lamellibranch shells on a seabed of muddy sand. There was some evidence that reef abundance was influenced by the availability of suitable substrata. 4. A belt of scattered reefs fringed much of the coastline of the loch with profuse reef development at two sites, where reef coverage exceeded 10% of the seabed. In terms of total abundance of Serpula 6ermicularis reefs, Loch Creran represents the major world site for reef development. It is concluded that the reefs of Loch Creran are of significant nature conservation importance and grounds for the establishment of conservation management are discussed.5. Reef development is apparently curtailed in areas of strong currents and high flushing rate. There is evidence that human activity has adversely influenced reef growth through the discharge of organic factory effluent and the physical disturbance caused by mooring ground tackle. Scallop dredging also represents a significant threat to the persistence of serpulid reefs. Methods of minimising damage to this rare and fragile feature are discussed.

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ABSTRACT1. The large size, patchiness and fragility of serpulid reefs present difficulties for the measurement of reef coverage for mapping and monitoring studies. Video transect measures of cover are assessed in terms of accuracy and sensitivity of the method for the identification of spatial or temporal changes.2. By comparison with direct in situ measurement of reef cover, it was found that still photography was capable of providing an accurate means for the measurement of the seabed coverage by individual reefs.3. By comparison of video and still photographic measurement of reef cover, it was found that video transects were capable of providing cover estimates of sufficient accuracy for conservation purposes, differing from still photographic estimates by 0.3% cover.4. Power analysis was employed on replicate video estimates of reef cover in order to determine the degree of replication required to identify different levels of spatial or temporal change in cover using video transects of different lengths. The modest level of replication required to identify changes in coverage as small as 25% of the initial value suggests that the use of video transects offers great potential in monitoring and mapping studies.

ABSTRACT1. This study describes investigations into mapping of the biogenic reefs produced by the polychaete worm, Serpula vermicularis, for the purposes of conservation management.2. Reef distribution throughout Loch Creran, Scotland, was mapped using a diver transect technique and was found to be restricted to a peripheral band, with a mean upper limit of distribution of 2.7 m. The mean lower limit was found to decrease with distance from the mouth of the loch, with a lower limit of 9.3 m in the lower basin rising to 6.6 m in the upper basin; the likely influence of a corresponding decrease in the upper depth distribution of muds is discussed.3. Through determination of the mean width of the reef band and coastline length, the areal extent of the reef band was estimated as 108 ha, revealing Loch Creran to harbour the most extensive known development of S. vermicularis reef habitat in the world.4. The utility of sidescan sonar in mapping serpulid reefs was examined in four of the major embayments. Reef material appeared as characteristic patterning on the sonargrams, with the morphology of individual larger reefs being discernible.5. Sidescan sonar was found to be particularly valuable for the identification and monitoring of threats to the conservation of serpulid reefs. Sidescan sonar surveying was found to facilitate identification of loss of habitat extent resulting from anthropogenic activities such as moorings, aquaculture installations and dredging and can also be used to monitor the potentially damaging activity of otter trawling. Further improvements in the mode of deployment of sidescan sonar are discussed.

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