ORIGINAL ARTICLE Infauna from Zostera marina L. meadows in Norway. Differences in vegetated and unvegetated areas STEIN FREDRIKSEN 1 *, ANNELIES DE BACKER 1 , CHRISTOFFER BOSTRO ¨ M 2 & HARTVIG CHRISTIE 3 1 Program for Marine Biology, Department of Biology, University of Oslo, Oslo, Norway; 2 A ˚ bo Akademi University, Environmental and Marine Biology, A ˚ bo, Finland; 3 Norwegian Institute for Water Research, Norway Abstract To investigate the importance of benthic vegetation for shallow infaunal assemblages, macroinvertebrates were sampled in Zostera marina meadows and in adjacent bare sand at three sites in the Skagerrak region and one in the Western part of Norway. A total of 3777 individuals were encountered, representing mainly the faunal groups Annelida, Nemertea, Echinodermata, Crustacea and Mollusca. Twice as many individuals were found in the Z. marina meadows compared to the bare sand. Oligochaetes were the most abundant group (29% of total number of individuals), followed by crustaceans (24%), polychaetes (18.5%) and molluscs (16%). Polychaetes showed the highest species number (42), followed by molluscs (30) and crustaceans (26). Multivariate cluster technique showed the highest similarities within sites and thereafter grouping according to the two different habitats; Zostera and sand. No regional differences were evident between the Skagerrak sites and the site in Western Norway, as the site from Western Norway grouped together with one of the Skagerrak sites. The high biodiversity in Zostera marina beds should have implications for the management of such areas. Key words: Biodiversity, infauna, sand, seagrass, Zostera marina Introduction Seagrasses are a characteristic feature of shallow intertidal and subtidal coastal areas. Seagrass beds may cover extensive areas (Green & Short 2003) and are regarded as highly productive habitats that host diverse food chains. Many species of invertebrates and fish use seagrass meadows as feeding and nursery grounds (Petersen 1918; Heck & Orth 1980; Pihl et al. 1994; Baden et al. 2003). Several investigations have shown that vegetated sediments support higher densities of infauna than nearby unvegetated sediments (Stoner 1980; Pihl 1986; Heck et al. 1989; Edgar et al. 1994; Bostro ¨m& Bonsdorff 1997; Webster et al. 1998). This is partly explained by the fact that the above-ground complex- ity of the meadows reduces water movement and increase sedimentation rates of fine particles and detritus. The above-ground vegetation provides ha- bitats and substrates for free-living animals and epiphytic animals and algae (Neckles et al. 1993; Fredriksen & Christie 2003; Fredriksen et al. 2005). Also, the below-ground rhizome network offers sedi- ment stability, creating favourable living conditions, including shelter from predation, for a wide range of infaunal organisms (Patriquin 1975; Orth 1977; Fonseca et al. 1983; Fonseca & Fisher 1986; Koch 2001; Bostro ¨ m et al. 2006). The ability of seagrasses to fulfil these roles is generally well documented (e.g. Lee et al. 2001 and references therein), but how and which infaunal species respond to the more complex sediment environment created by the seagrass, and how this response may vary across different spatial scales and geographic regions, is less well understood. The most common seagrass species in Norway is Zostera marina Linnaeus, 1753. This species is reported from the entire Norwegian coast, though is more scattered in the northern part (Bostro ¨m et al. 2003). The mechanisms behind the distribution of Z. marina are not well understood, but Z. marina seems to favour sheltered areas along the Norwegian *Correspondence: Stein Fredriksen, University of Oslo, Department of Biology, P.O. Box 1066, Blindem, Oslo 0316, Norway. E-mail: stein.fredriksen@bio.uio.no Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark Marine Biology Research, 2010; 6: 189200 (Accepted 11 May 2009; Published online 4 December 2009; Printed 15 March 2010) ISSN 1745-1000 print/ISSN 1745-1019 online # 2010 Taylor & Francis DOI: 10.1080/17451000903042461 Downloaded By: [Stiftung Alfred-Wegener-Inst f Pol] At: 12:02 11 May 2010