Distribution and Extent of Reefs

Detailed Monitoring of Reefs and Associated Communities

Recruitment

Physical and Chemical Parameters

Fishing

Monitoring requirements of serpulid reefs at present need to be tailored specifically towards Loch Creran, the only UK location where good examples are known to occur with certainty, and where a good baseline knowledge of extent, number and size of reefs exists for the whole loch (Moore, 1996).

In view of the rapid loss of reefs reported from Loch Sween in recent years, it is recommended that a broad indication of the extent and integrity of the reefs over the whole loch is carried out at least every 5 years, to include any changes in depth limits. A number of options would seem to be available for monitoring of the extent and integrity of serpulid reefs. Since they are clearly well developed structures they are likely to be visualised well with acoustic methods such as sidescan sonar and RoxAnnÔ , though there are sometimes limitations with RoxAnnÔ in very shallow waters. There is presently no experience with these methods for serpulid reefs, however. As always with acoustic methods, ground truthing would be required, although perhaps less extensively than with some other communities given the distinctiveness of the serpulid reefs. Diver surveys and video surveys (either diver-operated or ROV) both have potential for this.

ROV surveys have been successfully carried out on serpulid reefs in Loch Creran recently (Donnan, pers. comm.). Again, the large size and obviousness of the reefs makes them ideal for study by this method. Mapping of the distribution and integrity of reef areas could be carried out using ROV, perhaps in combination with acoustic methods. Towed video would, of course be far too damaging to be of use.

More detailed studies of one or more limited areas should be carried out more regularly, perhaps annually, including measurements of reef dimensions to give annual accretion rates, ratio of living / dead worms and observations on the general state of the reefs (siltation, epiphyte cover). The method of attaching portions of S. alveolata reef to plywood bases and subsequent measurement of volume (Bamber& Irvine, 1997; see section C above) may be adaptable to S. vermicularis for more detailed growth studies. Associated fauna should also be monitored. Study of associated fauna has so far been limited to diver surveys (e.g. Howson et al., 1996; Bosence, 1973; 1979), which work well only for those animals and plants visible at the surface of the colonies. Given the relatively open structure of the reefs, it is likely that many more species and organisms would be found by destructive sampling. However, this should be limited to very small amounts until the potential for regeneration of areas, either naturally or with provision of suitable substrata, has been established.

Unusually intense larval recruitment seems to be a crucial factor in serpulid reef development. Regular monitoring of recruitment using settlement plates would seem to be sensible in order to help to identify causes of any population changes.

It is difficult to make precise recommendations for monitoring of physical and chemical parameters, including water quality, since there is little knowledge of the requirements of the organism. However, suspended sediment levels, particularly in the settlement period, may be worth measuring in relation to larval settlement, since the presence of too much silt on the substratum may be inhibitory. Likewise, low oxygen levels are thought to limit downward extension of the reefs. In the typical enclosed loch situation in which the reefs occur low oxygen levels are likely to occur in the deeper waters; they should therefore be measured routinely.

Fishing operations in the loch should be monitored, primarily so that any potential damage might be more easily forestalled but also so that, in the event of any sudden damage, the likelihood that fishing was the cause can be determined.

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