DEVELOPMENT AND TESTING OF TOOLS FOR INTERCALIBRATION OF PHYTOPLANKTON, MACROVEGETATION AND BENTHIC FAUNA IN DANISH COASTAL AREAS Scientifi c Report from DCE – Danish Centre for Environment and Energy No. 93 2014 AARHUS AU UNIVERSITY DCE – DANISH CENTRE FOR ENVIRONMENT AND ENERGY [Blank page] DEVELOPMENT AND TESTING OF TOOLS FOR INTERCALIBRATION OF PHYTOPLANKTON, MACROVEGETATION AND BENTHIC FAUNA IN DANISH COASTAL AREAS Scientifi c Report from DCE – Danish Centre for Environment and EnergyNo. 93 2014 Jacob Carstensen Dorte Krause-Jensen Alf Josefson Aarhus University, Department of Bioscience AARHUS AU UNIVERSITY DCE – DANISH CENTRE FOR ENVIRONMENT AND ENERGY Data sheet Series title and no.: Scientific Report from DCE – Danish Centre for Environment and Energy No. 93 Title: Development and testing of tools for intercalibration of phytoplankton, macrovegetation and benthic fauna in Danish coastal areas Authors: Jacob Carstensen, Dorte Krause-Jensen, Alf Josefson Institution: Aarhus University, Department of Bioscience Publisher: Aarhus University, DCE – Danish Centre for Environment and Energy © URL: http://dce.au.dk/en Year of publication: March 2014 Editing completed: February 2014 Referees: Peter Henriksen, Department of Bioscience, Aarhus University Financial support: Danish Nature Agency (NST) Please cite as: Carstensen, J., Krause-Jensen, D., Josefson, A. 2014. Development and testing of tools for intercalibration of phytoplankton, macrovegetation and benthic fauna in Danish coastal areas. Aarhus University, DCE – Danish Centre for Environment and Energy, 85 pp. Scientific Report from DCE – Danish Centre for Environment and Energy No. 93. http://dce2.au.dk/pub/SR93.pdf Reproduction permitted provided the source is explicitly acknowledged Abstract: This report contributes to the development of indicators and assessment tools for ecological status classification according to the European Water Framework Directive as well as the intercalibration of the phytoplankton biomass indicator with Sweden and Germany. For the open coastal waters in the Kattegat and the Sound Denmark and Sweden have similar reference conditions for summer chlorophyll, whereas class boundaries are more strict in Denmark. Different indicators for phyto- plankton composition, based on the distribution of functional groups, have been tested and none of these indicators was found operational for assessing ecological status. Six indicators for macroalgae cover and composition have also been tested and three of these are suggested as the basis for an overall status assessment tool for macroalgae. The proposed assessment tool is modular and sufficiently flexible such that it can be readily adapted to other indicators and biological quality elements, for the WFD and other directives as well. The DKI indicator for benthic macrofauna integrates species sensitivity and diversity. Salinity is an important governing factor for diversity and therefore a salinity normalisation of the DKI is proposed. Keywords: Water Framework Directive, phytoplankton, macroalgae, angiosperms, indicator development, statistical models, reference condition, status classification. Layout: Anne van Acker Drawings: The authors/Anne van Acker Front page photo: Seabed off the coast of Stevns Klint. Photo: Karsten Dahl ISBN: 978-87-7156-061-9 ISSN (electronic): 2245-0203 Number of pages: 85 Internet version: The report is available in electronic format (pdf) at http://dce2.au.dk/pub/SR93.pdf Contents Summary 5 Sammenfatning 7 1 Introduction 9 2 Phytoplankton 10 2.1 Indicators of biomass 10 2.1.1 Linking biomass with nutrients 12 2.1.2 Effects of phytoplankton on eelgrass distribution 15 2.1.3 Intercalibration of summer chla with Sweden 16 2.2 Indicators of phytoplankton community 18 2.3 Conclusions 23 3 Macroalgae 25 3.1 Aim 26 3.2 Methods 26 3.2.1 Substratum 29 3.2.2 Physical-chemical variables 29 3.2.3 Statistical analyses of algal variables 29 3.3 Results 32 3.3.1 Indicator: Total cover 34 3.3.2 Indicator: Cumulative cover 37 3.3.3 Indicator: Cumulative cover of late-successionals 38 3.3.4 Indicator: Cumulative cover of opportunistic species 40 3.3.5 Indicator: Fraction of opportunistic species 42 3.3.6 Indicator: Number of late successionals 43 3.4 Boundary setting and assessment of macroalgae status 45 3.4.1 Uncertainty of the indicators 45 3.4.2 Sensitivity of the indicators to nutrient level 46 3.4.3 Status assessment for macroalgae 46 3.5 International intercalibration of vegetation indicators 49 3.6 Conclusions 49 4 Benthic fauna 51 4.1 Background 51 4.2 Is further normalization of DKI needed in addition to salinity? 52 4.2.1 Numerical methods 55 4.3 Results 55 4.3.1 Modelling species richness (alpha) and abundance within and among estuaries 56 4.3.2 Modelling pair-wise beta among estuaries 59 4.3.3 Modelling pair-wise beta between estuaries and open sea 61 4.4 Conclusions 63 4.5 Applicability of DKIver2 in a wider context 64 4.6 Re-description of DKIver2 66 5 Conclusions and recommendations 71 5.1 Phytoplankton 71 5.2 Macroalgae 71 5.3 Benthic fauna 72 6 References 74 Annexes 79 Summary This report describes the development of indicators and assessment tools for the Water Framework Directive’s (WFD) marine biological quality elements: phytoplankton, macroalgae and benthic macrofauna. It also addresses inter- calibration of these with Sweden and Germany. Phytoplankton biomass, which is quantified as the summer chlorophyll a concentration, increases with nutrient levels, most significantly with the total nitrogen concentration. The suggested reference conditions in Danish and Swedish coastal waters, sharing the same typology, are similar, but Den- mark has suggested a stricter boundary setting than Sweden, and these dif- ferences must be clarified. Phytoplankton composition across coastal water bodies is mainly governed by differences in salinity, but increasing levels of total nitrogen also suggest- ed a shift from dinoflagellates and other species to increasing dominance of diatoms. This shift is not perceived as a degradation of ecological status and the analyses of phytoplankton communities did not result in meaningful in- dicators sensitive to changes in nutrient levels. The scientific understanding of phytoplankton community responses to nutrient enrichment is not yet ripe for operational implementation in the WFD, and the implementation must await scientific advances in this field. Macroalgae cover and composition have been described by six different in- dicators, which are not biased by differences in depth and substrate of the monitoring observations. Three of these indicators, selected according to their sensitivity to total nitrogen and the uncertainty involved in their estimation, are proposed as the basis for assessing the ecological status of this biological quality element. An assessment tool is proposed for macroalgae, but the approach can be ap- plied more generally to other biological quality elements. The idea is to transform all indicators to a common EQR-scale, where status classes are equidistantly distributed. Indicators for the same biological quality element can be combined by weighted average, once transformed to the common EQR-scale. A quality of the proposed tool is its transparency from the indica- tor level to the overall assessment. The quality of soft sediment macrobenthic fauna may be measured by an in- dex integrating diversity and sensitivity components of species, the Danish quality index DKI, albeit with restricted applicability. An investigation was undertaken to identify important natural factors influ- encing local richness diversity (alpha) and consequently the Shannon diver- sity (H), one major component in the DKI index, to make the DKI operational in a wider context including Danish shallow coastal areas and estuaries. For this purpose, fauna data were used from an open sea area fringed by 17 es- tuaries. Both dispersal and environmental filtering were important in regu- lating alpha diversity in the estuaries, where salinity filtered primarily dis- persive species. So although dispersal limitation may determine the species 5 composition of alpha, the level of alpha is determined by salinity. Thus, for the purpose of normalizing, DKI correction for salinity makes sense. It is concluded that the original relationships between salinity and DKI com- ponents could be kept in the ‘new’ general version of DKIver2, re-described in this report with two minor amendments and more detailed suggestions of status determination procedure. It is recommended to use the salinity nor- malized DKIver2 index in general, and to use the 20th percentile of index data when evaluating status against a common set of boundaries for all types. 6 Sammenfatning Denne rapport beskriver udviklingen af indikatorer og tilstandsvurderings- værktøjer til brug for vandrammedirektivets (VRD) marine biologiske kvali- tetselementer: fytoplankton, makroalger og bentisk makrofauna. Rapporten behandler også interkalibreringen af disse kvalitetselementer med Sverige og Tyskland. Biomassen af fytoplankton, kvantificeret som koncentrationen af klorofyl a, vokser med mængden af næringssalte, mest signifikant for mængden af total kvælstof. De foreslåede referenceværdier for kystnære områder i Danmark og Sverige med samme typologi er sammenlignelige, hvorimod grænsevær- dierne mellem kvalitetsklasser er mere restriktive i Danmark end i Sverige. Det er vigtigt for interkalibreringen, at denne forskel mellem grænseværdier afklares mellem landene. Sammensætningen af fytoplankton i kystområder