Introduction to Monitoring

Introduction to Methods

This chapter discusses the options available for monitoring and surveillance of biogenic reefs, but does not make detailed recommendations for monitoring programmes as these would need to be tailored carefully to the needs of the individual SACs, and will be prepared by the relevant authorities. The information presented here relates mainly to available methods.

There are two types of monitoring which need to be considered by SAC managers: condition monitoring, which is synonymous with surveillance monitoring; and compliance monitoring. These can be defined as follows:

Condition monitoring (surveillance monitoring): monitoring designed to determine whether or not the feature is ‘maintaining favourable condition status’ (Burt, pers. comm.). Essentially this sort of monitoring must attempt to detect unanticipated impacts, including those which may be wide ranging, subtle or which only slowly become obvious (Hartnoll, in prep).

Compliance monitoring: monitoring designed to detect whether particular activities or disturbances are or are not having negative impacts upon the feature (Burt, pers. comm.).

In many instances the methods available for the two types of monitoring are essentially the same, particularly where effects at the level of populations or communities are being investigated (looking for changes in the extent of beds or in population structure, for example). However, the area covered may vary greatly. It may, for example, be possible to limit compliance monitoring for fishing impacts to a small area of biogenic reef in the safe knowledge that fishing does not occur elsewhere, while surveillance monitoring may have to be carried out over a much wider area.

In other cases compliance monitoring can be more focused than surveillance monitoring, for example where levels of contaminants (such as heavy metals in mussels) or physiological changes (such as imposex in gastropods caused by TBT contamination) are being investigated.

Choosing what monitoring methods are most suitable for any given area of SAC requires a more detailed level of knowledge of distribution (of both biotopes and human activities) and other circumstances than can be entered into in this report. However, a range of possible monitoring methods, some quite general and some more specific to the five main biogenic reef species, is given here.

Assessment of the reliability and practicalities of a variety of monitoring methods which might be useful for monitoring in SACs is presently underway (Hiscock, 1998a; Hiscock, 1998b). A report summarising two recent workshops on this subject, including interesting field exercises investigating consistency of methods between survey teams, together with a literature survey of methods, is also available (Worsfold & Dyer, 1997).

Details of monitoring options are given for each biogenic reef species in the subsequent sections (B-F). Since subtidal communities will be much more difficult to monitor than intertidal ones, and are more likely to rely on modern technology, a brief overview of some of the available methods is given here.

For many of the subtidal reefs, their distinctive topography and texture renders it likely that modern acoustic monitoring methods such as RoxAnnÔ and sidescan sonar may be useful, and these are referred to several times in this chapter. RoxAnnÔ interprets the signals from an ordinary shipboard echosounder of the type routinely used for measuring depth, and gives information on the ‘hardness/softness’ and ‘roughness/smoothness’ of the bottom, which by calibration against known seabed types can be used to rapidly collect information on seabed type over large areas (for detailed technical information see Chivers et al., 1990). Information is obtained only from the seabed directly below the boat. Sidescan sonar uses a dedicated sonar source towed on a wire behind the boat, relatively near to the seabottom, which ‘scans out’ a signal to either side many times per second. By interpretation of the signal bounced back from the seabed an image of the seabed, which is based upon both topography and ‘hardness/softness’ of the bottom, can be produced. This image can typically cover an area of up to a few hundred metres on either side of the boat.

Worsfold & Dyer (1997) contains a useful overview of the use and limitations of RoxAnnÔ bottom discrimination, (although for more detailed assessment of the technique’s application see Davies et al., 1997). There was no detailed discussion of sidescan, although it was pointed out that no references to its use in the mapping of biological features or biotopes had been found. In fact, use of sidescan for mapping biological features has been successfully used where the features are physically distinct and/or obvious, including for a number of biogenic reef features, particularly Modiolus reef areas. Other features such as maerl beds in Scottish sea lochs have also been mapped (Foster-Smith & Davies, in prep). Holt et al. (unpublished) were able to map unusual reef structures formed by Modiolus off the north end of the Isle of Man, as well as nearby Ophiothrix beds; Magorrian et al. (1995) were able to map Modiolus reefs in Strangford Lough. Very large Modiolus bioherms have been mapped in Canada using relatively long range sidescan (Wildish et al., in press). Subtidally, areas of semi-infaunal Mytilus in the Tay Estuary have recently been mapped by sidescan (Silke Wewetzer, pers. comm.). Rees and co-workers had considerable success in mapping Modiolus beds off the Lleyn Peninsula using acoustic methods, particularly RoxAnnÔ .

Monitoring of the population structure of the reef forming species and the associated flora and fauna in subtidal communities will be problematical. Options include broadscale surveys using towed video or ROV, although the former might in some cases cause physical damage, hand held diver video, fixed quadrat photography, or diver surveys using Abundance scale Checklist at Exact locations (ACE surveys) or transect/quadrat counts. Video surveys cover larger areas than fixed quadrat photography or diver surveys but only limited conspicuous organisms can confidently be quantified. ACE surveys and transect/quadrat surveys are expensive but more likely to detect change. All of these methods would be limited to macrobiota. Monitoring of infauna and cryptic fauna can only be carried out with destructive sampling techniques which are expensive to process and, given the state of present knowledge of biogenic reef communities, should take a lower priority for now.

Hartnoll (in prep) notes that likely improvements to methodology for work in the sublittoral in the near future will be of great value for survey and monitoring of circalittoral hard substrata, and similar arguments apply in respect of sublittoral biogenic reefs. These improvements relate mainly to increased dive times due, for example, to increasing use of nitrox gas mixtures and rebreathing apparatus, improved location, communication, site marking and recording equipment for divers, and further development and use of non diving technologies including ROV and automatic dataloggers.

Problems associated with determining acceptable limits of change

Sabellaria alveolata

Sabellaria spinulosa

Modiolus modiolus

Mytilus edulis

Serpula vermicularis

References