The purpose of any investigation is to define the conservation interest, their quality and distribution.

On any site there will almost certainly be a need to undertake a survey to at least identify, if not to characterise, the biological features present, and assess their conservation importance and sensitivity to particular water quality parameters. Such surveys should follow guidelines currently being developed by the UK Marine SACS Project (see Hiscock 1998), although the need for comparison with historical studies may require modification in some cases. Trials to develop monitoring techniques and strategies to inform these guidelines have highlighted that at some sites, e.g. Loch nam Madadh lagoons, survey work may be a relatively damaging activity particularly where the site is subject to little other activity (Downie pers. comm.). Any negative implications of a survey would need to be weighed against the benefits of undertaking such work.

Any survey undertaken must be quantitative as well as qualitative, in order to detect any changes which may occur. The scope of such surveys will be site dependent, but for example should include some or all of the following (in approximate priority order):

• spatial distribution (mapping), species composition and quality of vegetation, such as seagrasses, Ruppia, charophytes, pondweeds and reed beds;

• presence and distribution of specialist lagoonal invertebrates;

• distribution and species composition of other invertebrate communities;

• distribution and species composition of fish populations;

• spatial distribution (mapping) and species composition of algae (benthic and epiphytic) which may affect communities of conservation importance;

• spatial distribution (mapping) and species composition of grazing invertebrate populations which may affect communities of conservation importance;

• studies of bird populations which may affect communities of conservation importance (e.g. by grazing, preying upon other species, or nutrient input);

• distribution and species composition of plankton (phyto- and zooplankton), including frequency and species composition of blooms if relevant.

Timing, frequency and spatial extent (i.e. no. of sites surveyed) of the above surveys will vary for each component, and to some extent depend upon financial and time resources as well as the characteristics of the site. Seasonal variation in communities should be taken into account when planning such surveys.

There is a need to take account of information on the known sensitivity of biological features of interest. Such information, if available, is likely to be derived from studies elsewhere or from relevant reviews such as those undertaken as part of the UK Marine SACs Project (see, for example, Davison and Hughes 1998, Elliott et al 1998) as well as herein.

A number of conservation features of interest in the Fleet appear to have been, or potentially could be, affected by impacts from nutrient enrichment. In priority order these are:

• charophyte species – directly, i.e. physiological response, and indirectly, i.e. competition from opportunistic species.
• seagrass and tasselweeds – indirectly, i.e. competition from opportunistic species,
• fauna associated with charophytes, seagrass and tasselweed beds – indirectly through impacts on host vegetation.

There is a suggestion that another indirect impact is the exposure of fish species to toxic phytoplankton as a result of blooms caused by nutrient enrichment.

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