Determining the presence and extent of the biotope complex

Initial characterization of the biological community

Monitoring of change in the biotope

Having outlined the capabilities and limitations of the various monitoring techniques, it is possible to suggest a provisional scheme by which the distribution, composition and ‘health’ of an example of the biotope complex within an SAC could be assessed. It is assumed that although the main responsibility for this work will rest with a local SAC site officer, manpower and technical support will be available from the relevant national conservation agency (EN, SNH, CCW, DOE/NI) and from the JNCC. Collaboration with academic experts based at universities or public sector research institutions should also be strongly encouraged and would be essential if certain options (eg. burrow resin-casting) were to be pursued.

The presence of an example of the biotope complex within an SAC can be established by diving (eg. MNCR survey), observation using towed video or ROV, by consulting literature records of species distributions, or simply inferred from the existence of a local Nephrops fishery. The spatial extent of the relevant sedimentary habitats would be most effectively mapped using RoxAnn^TM, backed up by localized grab sampling or direct observation (diving, towed video, ROV). This initial habitat survey has already been achieved for many of the candidate SACs.

For an assessment of the scientific and conservation importance of an example of the biotope complex within an SAC, its species composition must be determined so that it can be compared with examples known from elsewhere. For the larger animals this requires a visual survey, either by divers (if water depth allows), towed video or ROV. Species such as Nephrops norvegicus, Goneplax rhomboides, Cepola rubescens, Pachycerianthus multiplicatus and the three sea pens are highly conspicuous and easily identified, either first-hand or on videotape. Identification of the more cryptic, deeper-burrowing megafauna (echiuran worms, thalassinidean mud-shrimps) relies on observation of relatively subtle diagnostic features of burrow openings and ejecta mounds, since the animals themselves are unlikely to be seen at the sediment surface. Guides to the identification of megafaunal surface traces can be found in Atkinson (1986), Atkinson & Nash (1985) and Hughes et al. (1996b, for Maxmuelleria lankesteri). A detailed key is provided by Marrs et al. (1996). In general, characterization of this element of the fauna can be fairly difficult even for experienced observers. Definitive identifications can be obtained by the resin-casting of burrows (Atkinson & Chapman, 1984), but this is a specialized and time-consuming technique requiring considerable expertise, and only feasible in relatively shallow waters (< 30 m). In the UK, this expertise exists in only a few academic institutions.

The composition of the sediment macrofauna can only be determined by examination of samples taken in grabs or cores. This is a highly labour-intensive process requiring taxonomic expertise. Numerous academic institutions and private environmental consultancies around the UK have the capacity to carry out these analyses, but financial costs may be considerable.

It is recommended that the initial faunal survey of a sedimentary biotope within an SAC should involve identification of burrowing megafauna by experienced observers using towed video or ROV recordings. These should be backed-up by first-hand diving observations if water depth allows, but enough is now known about the surface features associated with individual species for reliable identifications to be possible from videotape if good image quality is achieved. Resin-casting is probably unnecessary at the initial stage but would be worth pursuing if the visual survey reveals distinctive burrow types of unknown origin (eg. Tuck & Atkinson, 1995) in water depths accessible to divers. A small number of grab or core samples should also be taken in each of the major sediment types identified for characterization of the smaller fauna. A detailed consideration of the merits of different sampling strategies relative to the information obtained can be found in Kingston & Riddle (1989).

If a biotope example within an SAC is deemed to be important for scientific or conservation-related reasons, it will be necessary to establish a programme of repeated observations or measurements to determine whether changes are occurring in any important parameters, and to identify the causes of any observed change. The practical objectives will clearly be to keep the time, labour and financial cost involved as low as possible while maximising the usefulness of the information obtained.

For routine monitoring, the abundance of the larger, more conspicuous fauna can be taken as an indicator of the general ‘health’ of the ecosystem. As discussed in Chapter VI, sea pens and Nephrops norvegicus are the species likely to be directly affected by trawling or organic enrichment (the most likely agents of change under current circumstances). The abundance of the larger animals can be assessed relatively easily (see detailed discussion below), and is a more immediately-apparent indicator of change than the results of costly and time-consuming macrofaunal analyses. The MNCR biotope classification system is explicitly based on the larger organisms recorded on diving surveys, and so reflects this emphasis.

Visual survey methods

Features to quantify

Monitoring potential agents of environmental change

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