The Conservation of Freshwater Macroinvertebrate Populations: a Community-Based Classification Scheme
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AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS Aquatic Conserv: Mar. Freshw. Ecosyst. 14: 597–624 Published online 6 October 2004 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/aqc.630 The conservation of freshwater macroinvertebrate populations: a community-based classification scheme RICHARD CHADD* and CHRIS EXTENCE The Environment Agency of England & Wales (Anglian Region, Northern Area), Waterside House, Waterside North, Lincoln, UK ABSTRACT 1. A novel conservation indexing protocol is presented which aims to summarize aquatic macroinvertebrate data obtained from inland flowing- and still-water sites in Great Britain. Unlike other summary expressions of conservation value, the Community Conservation Index (CCI) accounts for community richness in the final analysis, as well as the relative rarity of species present. 2. Examples are provided to show how taxonomically rich ecosystems can obtain very high values of CCI that are broadly equivalent to CCI scores obtained from other sites supporting nationally rare species. In addition, the CCI is capable of local adjustment, to accommodate nationally common species occurring outside their normal range. 3. Examples show typical CCI outputs from a range of riverine and still-water habitats, and illustrate how this analysis can help in the day-to-day assessment and management of both lotic and lentic ecosystems. The index has already been used in legal submissions for public inquiries on Sites of Special Scientific Interest protected under British law and has contributed to the designation of such sites. It has also been used to inform management decisions on sites selected as candidate Special Areas of Conservation and as an operational tool using routinely obtained datasets. 4. The CCI provides an empirical basis for conservation initiatives, programmes and strategies, by producing a summary of aquatic invertebrate data over any appropriate scale of time and space. Furthermore, the final analysis need not be constrained by distribution of nationally rare species, but can indicate exceptionally rich or regionally unusual invertebrate populations. Copyright # 2004 John Wiley & Sons, Ltd. KEY WORDS: Community Conservation Index; rare species; invertebrate conservation INTRODUCTION Consideration of aquatic macroinvertebrate communities is regarded as a useful tool for assessing the conservation status of inland wetland habitats, often for the purpose of influencing their ultimate fate. Such assessments may compare individual water bodies within a larger complex, to provide local management recommendations (Environment Agency, 1997; Painter, 1999), or to demonstrate a general conservation *Correspondence to: Richard Chadd, Environment Agency, Stepping Stone Walk, Winfrey Avenue, Spalding, Lincolnshire PE11 1DA, UK. Copyright # 2004 John Wiley & Sons, Ltd. Received 17 March 2003 Accepted 5 March 2004 598 R. CHADD AND C. EXTENCE principle (Collinson et al., 1995; Killeen, 1998; Standen, 1999). They may also be used to set the value of a particular site or habitat type, or a whole series of interrelated water bodies, in a national or international context (Environment Agency, 1993, 1997; Guest, 1997; Palmer, 1999; Harrison, 2000). Such information forms an integral part of the decision-making process for initiatives designed to protect and manage the aquatic environment, such as national abstraction licensing policies or asset management plans (Environment Agency, 2002). It also provides an essential contribution to national or international legislative requirements relating to biodiversity, such as the European Habitats Directive (EEC, 1992) and the resultant UK Conservation Regulations (HMSO, 1994). The usual approach when analysing available datasets is to discuss local, national or global value in subjective terms, such as the presence of one or more known rarities in the fauna. The judgement of rarity is set, in turn, by using published lists or reviews (e.g. Shirt, 1987; Bratton, 1991; Wallace, 1991) or atlases (e.g. Merritt et al., 1996; Kerney, 1999; Huxley, 2003). Alternatively, subjective judgements may use simple comparisons of species assemblages, so as to determine the degree of species richness associated with a site or region and/or their comparability with assemblages from similar waters elsewhere (Harrison, 2000). More objective approaches may involve the calculation of diversity parameters to derive a measure of species richness (Standen, 1999), or multivariate analysis to define community distinctiveness. This, in turn, may be augmented by a numerical index of species rarity (e.g. Collinson et al., 1995; Killeen, 1998; Pond Action, 1999). Community distinctiveness and species richness may also be used as a means of defining wetland typology and hydrology, so as to identify large-scale management options on specifically targeted areas. For example, studies of dry and intensively farmed ephemeral wetlands in the Prairie Pothole Region of North America (Euliss et al., 2001) allowed identification and evaluation of such habitats, even following draining or infilling, or when the wetlands were seasonally dry. The intention was for the technique to contribute subsequently to management strategies for the whole region’s wetland complex, focused on ‘value’ of particular sites as well as their hydrological state. In England and Wales, work on ponds and canals has led to the development of a ‘multimetric’ approach, known as the Predictive System for Multimetrics (PSYM). This uses a range of plant and invertebrate measures (‘metrics’) to define the general ecological condition of such wetlands (Environment Agency and Ponds Conservation Trust, 2002). Such metrics include, for example, the number of families of Coleoptera present. The assumption is that an ‘undegraded’ or ‘ideal’ ecology, determined for any pond or canal by reference to a national dataset obtained from still waters throughout England and Wales, can allow the determination of an overall quality state by comparing metrics obtained at a site with those predicted for it. This, in turn, may broadly equate to a measure of conservation status, although PSYM does not allow for invertebrate species rarity (one of the metrics used is an ‘uncommon species index’, but this is only applied to plants). Strictly speaking, PSYM is more suitable for assessing water quality rather than evaluating conservation status or potential. None of these approaches, however, combines a generalized measure of species rarity, as an index, with a numerical measure of taxon richness to derive an overall index of the conservation value of the whole community. Consequently, habitats supporting rare species cannot be compared directly with those colonized by invertebrate assemblages of unusually high richness, but lacking any particular rarities. It could, nevertheless, be argued that the latter are as distinct and worthy of protection as the former, and those habitats which combine both high taxon richness and high species rarity need particular acknowledgement. Furthermore, current indices, such as the Species Rarity Index (SRI) (Collinson et al., 1995; Pond Action, 1999), tend to rely entirely on species defined as nationally rare within published lists of status, such as the Red Data Books (RDBs; Shirt, 1987; Bratton, 1991). Species of limited distribution locally or nationally, but with no special status, do not contribute to the index score in this case. SRI is also limited by the fact that it cannot be applied to most riverine habitats, since it was specifically designed as a still-water assessment protocol. Copyright # 2004 John Wiley & Sons, Ltd. Aquatic Conserv: Mar. Freshw. Ecosyst. 14: 597–624 (2004) CONSERVATION OF FRESHWATER MACROINVERTEBRATE POPULATIONS 599 To some degree, many of the shortcomings in previous approaches to conservation assessment have been addressed by the development of the System for Evaluating Rivers for Conservation (SERCON; Boon et al., 1996, 1997). In this approach, rarity within invertebrate assemblages is allowed for by the use of status- weighted scores and species richness is derived from taxon counts. ‘Representativeness’ is incorporated by using predicted taxon lists and comparing these with the results obtained. The output is then adjusted by the presence of non-native species to characterize ‘naturalness’. Habitat availability is also assessed and weighted accordingly. The system also integrates macrophyte, fish and bird data in the overall assessment of a river site. SERCON is not, however, applicable to still waters and is not particularly simple to apply, as it requires access to predictive models and a large number of data sources. Therefore, the need exists for an index to address these various issues. Ideally, such an index should also allow for local flexibility, so as to emphasize communities that include nationally common species found outside their expected range. This principle has previously been used for expressing conservation status of ponds in East Yorkshire, UK, in terms of the resident hydrophytes (Linton and Goulder, 2000). Finally, the methodology should be robust enough to apply to all inland aquatic habitats: riverine or still water, permanent or temporary, freshwater or brackish. The technique described in this paper aims to summarize the conservation value of invertebrate communities in any inland aquatic habitat in Great Britain, in terms of a simple, adaptable and readily applied index (the Community Conservation Index (CCI)) which incorporates elements of both