title: Clonal architecture in an intertidal bed of the dwarf eelgrassZostera noltiiin the Northern Wadden Sea: persistence through extreme physical perturbation and the importance of a seed bank.
abstract: Genotypic structure and temporal dynamics of the dwarf seagrass,Zostera noltii,were studied in an intertidal meadow that has persisted since prior to 1936 near the Wadden Sea island of Sylt. Samples were collected from two 10 × 10 m plots separated by 250 m from May 2002 to June 2005 and from four 1 × 1 m plots from June 2003 to September 2004. All the samples were genotyped with nine microsatellite loci. No genotypes were shared between the plots separated by 250 m. Genetic diversity was higher in the Wadden Sea than in the other regions of its geographic range. The average clone size (genets) (SD) in the two plots was 1.38 (0.26) and 1.46 (0.4) m², respectively, with a range up to 9 m² and <20% persisted for >4 years. A high genetic and genotypic diversity was maintained by annual recruitment of seedlings despite a dramatic decrease in ramet density that coincided with the severe heat stress event of 2003. Fine-scale (1 m²) analysis suggested that extensive loss of seagrass cover precluded space competition among the genets, while a persistent seed bank prevented local extinction. Long-term persistence ofZ. noltiimeadows in the intertidal Wadden Sea was achieved by high genet turnover and frequent seedling recruitment from a seed bank, in contrast to the low diversity observed in large and long-living clones ofZ. noltiiand other seagrasses in subtidal habitats.
authors.affiliation: Department of Marine Benthic Ecology and Evolution, Centre for Ecological and Evolutionary Studies, Biological Centre, University of Groningen, Kerklaan 30, 9750 AA Haren, The Netherlands.
authors.forename: Andreas M
authors.initials: AM
authors.lastname: Zipperle
authors.affiliation: Department of Marine Benthic Ecology and Evolution, Centre for Ecological and Evolutionary Studies, Biological Centre, University of Groningen, Kerklaan 30, 9750 AA Haren, The Netherlands.
authors.forename: James A
authors.initials: JA
authors.lastname: Coyer
authors.affiliation: Alfred Wegener Institute for Polar and Marine Research, Wadden Sea Station Sylt, 25992 List, Germany.
authors.forename: Karsten
authors.initials: K
authors.lastname: Reise
authors.affiliation: Department of Marine Benthic Ecology and Evolution, Centre for Ecological and Evolutionary Studies, Biological Centre, University of Groningen, Kerklaan 30, 9750 AA Haren, The Netherlands.
authors.forename: Eelo
authors.initials: E
authors.lastname: Gitz
authors.affiliation: Department of Marine Benthic Ecology and Evolution, Centre for Ecological and Evolutionary Studies, Biological Centre, University of Groningen, Kerklaan 30, 9750 AA Haren, The Netherlands.
authors.forename: Wytze T
authors.initials: WT
authors.lastname: Stam
authors.affiliation: Department of Marine Benthic Ecology and Evolution, Centre for Ecological and Evolutionary Studies, Biological Centre, University of Groningen, Kerklaan 30, 9750 AA Haren, The Netherlands.
authors.forename: Jeanine L
authors.initials: JL
authors.lastname: Olsen