PRIMARY RESEARCH PAPER A comparison of national approaches to setting ecological status boundaries in phytobenthos assessment for the European Water Framework Directive: results of an intercalibration exercise Martyn Kelly Æ Cathy Bennett Æ Michel Coste Æ Cristina Delgado Æ Franc ¸ois Delmas Æ Luc Denys Æ Luc Ector Æ Claude Fauville Æ Martial Ferre ´ol Æ Malgorzata Golub Æ Amelie Jarlman Æ Maria Kahlert Æ John Lucey Æ Bernadette Nı ´ Chatha ´in Æ Isabel Pardo Æ Peter Pfister Æ Joanna Picinska-Faltynowicz Æ Juliette Rosebery Æ Christine Schranz Æ Jochen Schaumburg Æ Herman van Dam Æ Sirje Vilbaste Received: 30 July 2008 / Revised: 8 October 2008 / Accepted: 25 October 2008 / Published online: 19 November 2008 Ó Springer Science+Business Media B.V. 2008 Abstract The European Union (EU)’s Water Frame- work Directive (WFD) requires that all Member States participate in intercalibration exercises in order to ensure that ecological status concepts and assessment levels are consistent across the EU. This paper describes one such exercise, performed by the coun- tries in the Central/Baltic Geographical Intercalibration Group stretching from Ireland in the west to Estonia in the east and from the southern parts of Scandinavia to the northern regions of Spain and Italy (but excluding alpine regions, which were intercalibrated separately). In this exercise, methods used to measure ecological Handling editor: J. Padisak M. Kelly (&) Bowburn Consultancy, 11 Monteigne Drive, Bowburn, Durham DH6 5QB, UK e-mail: MGKelly@bowburn-consultancy.co.uk C. Bennett SEPA, Greyhope Road, Torry, Aberdeen AB11 9RD, UK M. Coste  F. Delmas  M. Ferre ´ol  J. Rosebery REQUE Research Unit, Cemagref – Bordeaux Centre, 50, Avenue de Verdun, Gazinet, France C. Delgado  I. Pardo Departamento de Ecologı ´a y Biologı ´a Animal, Universidad de Vigo, Campus Lagoas-Marcosende, 36310 Vigo, Spain L. Denys Research Institute for Nature and Forest, Kliniekstraat 25, 1070 Brussel, Belgium L. Ector  M. Ferre ´ol Centre de Recherche Public – Gabriel Lippmann, 41 rue du Brill, 4422 Belvaux, Luxembourg C. Fauville Laboratory of Freshwater Ecology, URBO FUNDP, Rue de Bruxelles 61, 5000 Namur, Belgium M. Golub Institute of Environmental Protection, ul. Kolektorska 4, 01-692 Warsaw, Poland A. Jarlman Jarlman HB, Stora Tva ¨rgatan 33, 22352 Lund, Sweden M. Kahlert Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, P.O. Box 7050, 75007 Uppsala, Sweden J. Lucey Environmental Protection Agency, Butts Green, Kilkenny, Ireland B. Nı ´ Chatha ´in Shannon River Basin District Project, Mulkear House, Newtown Centre, Annacotty, Co. Limerick, Ireland 123 Hydrobiologia (2009) 621:169–182 DOI 10.1007/s10750-008-9641-4