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Seagrass) Within the EU Water Framework Directive: a UK Perspective

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Seagrass) Within the EU Water Framework Directive: a UK Perspective Marine Pollution Bulletin 55 (2007) 181–195 www.elsevier.com/locate/marpolbul Angiosperms (seagrass) within the EU water framework directive: A UK perspective Jo Foden a,*, D.P. Brazier b a Centre for Environment, Fisheries and Aquaculture Science (CEFAS), Pakefield Road, Lowestoft, Suffolk NR33 0HT, United Kingdom b Cyngor Cefn Gwlad Cymru/Countryside Council for Wales, Maes y Ffynnon, Penrhosgarnedd, Bangor, Gwynedd, LL57 2DN, United Kingdom Abstract Taxonomic composition, the presence of disturbance-sensitive species and abundance are attributes for monitoring the status of mar- ine angiosperms; a biological quality element required for assessment of environmental condition under the Water Framework Directive (WFD). Their relevance for defining the ecological status of UK water bodies and the establishment of reference conditions for these attributes are described. Founded on quantitative measurements of these attributes, a set of metrics has been developed for monitoring and assessment of the only truly marine angiosperms, seagrass. The proposed metrics are presented and tested against a variety of littoral and sublittoral UK seagrass beds. In combination they express the cumulative response of marine angiosperms to different levels of anthropogenic disturbance. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Marine angiosperms; Seagrass; UK; Water Framework Directive; Reference conditions; Ecological status 1. Introduction There are no detectable changes in angiosperm abundance due to anthropogenic activities’’. Annex V of the Water Framework Directive WFD, In CWs ‘‘all disturbance-sensitive ... angiosperm taxa 2000/60/EC states that angiosperms, phytoplankton, mac- associated with undisturbed conditions are present. The levels roalgae, benthic invertebrate fauna and fish are the biolog- of ... angiosperm abundance are consistent with undisturbed ical quality elements to be used in defining the ecological conditions’’ (WFD, 2000/60/EC, Annex V). status of a transitional or coastal water body. Seagrasses These descriptors set out the attributes to be used in are the only truly marine angiosperms and can be used monitoring seagrass and the standards to be reached in a for monitoring purposes because they are sensitive to water body for it to be considered free from anthropogenic human disturbance (Short and Wyllie-Echeverria, 1996). influences, i.e. at reference condition. They can be summa- All UK seagrass species are included in the UK Biodiver- rised as taxonomic composition (including presence of dis- sity Action Plan, 1994, and are considered nationally turbance-sensitive taxa) and abundance (determined by scarce. Reference conditions for angiosperms in transi- seagrass shoot density and spatial extent), in both CWs tional (TW) and coastal waters (CW) are defined: and TWs. Three metrics have been developed that apply In TWs ‘‘the angiosperm taxonomic composition corre- to littoral and sublittoral seagrass beds in both TWs and sponds totally or nearly totally with undisturbed conditions. CWs, to meet the monitoring requirements and are pre- sented herein: * Corresponding author. • Taxonomic composition (presence of disturbance-sensi- E-mail address: [email protected] (J. Foden). tive taxa). 0025-326X/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.marpolbul.2006.08.021 182 J. Foden, D.P. Brazier / Marine Pollution Bulletin 55 (2007) 181–195 • Abundance, determined by seagrass shoot density. past history of events, e.g. extreme wind, may play a signif- • Abundance, measured by seagrass bed spatial extent. icant role in the present distribution and density of seag- rasses in most systems. Field surveys are likely to include sites representing many different developmental stages of 1.1. Establishing reference conditions seagrass beds, ranging from bare sediment, initial colonisa- tion, to fully developed meadows (Krause-Jensen et al., The WFD requires European Member States to type 2003). water bodies according to specific factors: for TWs these Establishing reference conditions based on historic data are mixing characteristics, salinity, tidal range, exposure, and expert judgement is possible in some locales, however, depth and substrate; and for CWs, salinity, tidal range there has not been a national seagrass monitoring pro- and exposure ((WFD) Directive 2000/60/EC). A water gramme in the UK. For many sites monitoring on a local body typology classification has been designed for the scale has likely employed one of a variety of methods, result- UK to fulfil these requirements (UKTAG, 2003). Type- ing in data that cannot be readily compared across sites. specific biological reference conditions must be set using Type-specific reference conditions cannot be accurately one of three approaches; spatially based, based on model- determined from such mixed and patchy documentation, ling, or derived using a combination of these methods. but determination of site-specific reference conditions is fea- For spatially based type-specific biological reference condi- sible in some cases. For example, Kay (1998) conducted a tions, wherever possible EU Member States are developing comprehensive review of the knowledge of seagrass beds a reference network for each surface water body type. Pre- around the Welsh coast for the Countryside Council for dictive models or hindcasting methods should use histori- Wales (CCW). The review pools verbal, written and numeric cal, palaeological and other available data. Where it is data from a wide variety of sources and provides summaries not possible to use these methods, expert judgement may of knowledge of individual beds. Such historic data may be be used to establish such conditions (WFD Annex II 1.3). suitable for setting site-specific reference conditions for sea- In the UK the first approach of establishing spatially grass beds, provided they are considered accurate and quan- based type-specific reference conditions for seagrass from tifiable. This approach has been adopted by other European a reference network for each surface water body type is Member States; for example Krause-Jensen et al. (2005) problematic. Whilst there may exist a few potential sea- found the use of type-specific reference conditions for sea- grass reference sites in UK TWs and CWs, reference sites grass depth limits in Denmark risked misinterpretations of are not extant in all types, so type-specific reference condi- ecological status for many water bodies. Site-specific refer- tions cannot be set using this approach. Seagrass distribu- ence conditions, however, facilitated the adjustment of tion, abundance and ecological condition are highly monitoring activities according to local conditions. variable and sensitive, and causes of deviation from pro- Where no historic data exist, baseline surveys must be posed reference conditions are multiple, may frequently conducted and expert judgement relied upon to identify be obscure and are rarely quantifiable. The alternative site-specific reference conditions. The objective is for a sea- approaches for setting reference conditions were consi- grass bed’s taxonomic composition and abundance to be in dered. equilibrium (tolerating natural variability) at the maximum The second approach is to use predictive models. Ideally potential for the site. Assignation of reference conditions is it would be possible to identify locations with suitable envi- described further in Section 2. ronmental parameters for seagrass and therefore to predict Annex V 1.4.1 of the Directive states, ‘‘the results of the presence; enabling the targeting of monitoring directly to (classification) systems ... shall be expressed as ecological extant seagrass beds and potential sites. Despite best model- quality ratios (EQR) for the purposes of classification of ling efforts in recent years (e.g. Fonseca et al., 2002; Krause- ecological status. These ratios shall represent the relationship Jensen et al., 2003), however, such accurate prediction has between the values of the biological parameters observed for proved to be elusive for some of the following reasons. a given body of surface water and the values for these param- Krause-Jensen et al. (2003) were able to evaluate the impor- eters in the reference conditions applicable to that body. The tance of light, wave exposure, slope, salinity and depth in ratio shall be expressed as a numerical value between zero regulating sublittoral eelgrass cover in Danish coastal and one, with high ecological status represented by values waters at different depth intervals. Even so, the power of close to one and bad ecological status by values close to zero’’ the models was limited and prediction of eelgrass cover (WFD, 2222/60/EC, Annex V). Fig. 1 illustrates this con- under specific conditions was not adequate for management cept. The comparison of monitoring results with the refer- purposes. For example, in some locales, eelgrass was absent ence conditions derives the EQR. The values of the EQR or exhibited very low cover in shallow waters despite suffi- established for each ecological status class must ensure that cient light. Such discrepancies suggest other factors are act- the water body meets the normative definition for that sta- ing on seagrass distribution; for example, grazing by tus class as given in Annex V (Tables 1.2, 1.2.3. or 1.2.4). wildfowl, fish or invertebrates, sediment conditions, epi- As such the reference conditions form the anchor for the phytes and free-living macroalgae, extreme low tides and whole ecological assessment. Ecological
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