Habitat characteristics and spatial arrangement affecting the diversity of fish and decapod assemblages of seagrass (Zostera marina) beds around the coast of Jersey (English Channel) Emma L. Jackson * , Martin J. Attrill, Malcolm B. Jones Marine Biology and Ecology Research Centre, School of Biological Sciences, University of Plymouth, Drake Circus, Plymouth PL4 8AA, UK Received 4 November 2004; accepted 23 January 2006 Available online 4 May 2006 Abstract Recent research and management plans for seagrass habitats have called for landscape level approaches. The present study examines the spatial utilisation of subtidal seagrass beds by fish and decapods around the coast of Jersey (49  N 02  W). A hierarchical scale of landscape configuration and the plant characteristics of eight seagrass beds were measured and the contributions of these variables as predictors of the properties of the fish and decapod assemblages were evaluated using multiple linear regression models. The results indicated that total diversity had a negative relationship with transect heterogeneity and total species number had a weak negative association with increasing fragmentation. Both total diversity and total species number showed a positive relationship with depth. In fact, in all models of species number and densities, values were higher in deeper seagrass beds. Total decapod density increased with aggregation of seagrass patches within a landscape. In addition to landscape configuration, smaller-scale structural changes in both canopy height and epiphyte load appeared to influence densities of decapod crustaceans. At night, fewer patterns could be explained by the independent variables in the model. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: seagrass; Zostera marina; spatial scale; landscape ecology; fish; decapod crustaceans 1. Introduction In the United Kingdom, seagrass beds (Zostera spp.) are one of the focal biotopes for Marine Habitat Action Plans in the UK (part of the UK Biodiversity Action Plan) and are a named component of ‘‘Lagoons and Shallow Sandbanks’’ within the European Union Habitats directive (92/43/EEC). The inclusion of seagrass is due in part to the belief that they support relatively high biodiversity compared to other habitats. Despite this statutory recognition, few studies have assessed the biodiversity value of different seagrass beds in the United Kingdom, particularly for fish and mobile macroin- vertebrates (but see Pihl Baden and Pihl, 1984; Costa et al., 1994) and seagrass beds have only been mapped locally in this region (Gle ´marec et al., 1997). In Jersey one of the priority objectives for fisheries man- agers is to protect overall biodiversity; one of their focal hab- itats is seagrass beds. The habitat ‘‘value’’ of seagrass beds has been shown to vary with coastal location, depth, proximity to other habitats and position within a bay, lagoon or estuary. At the level of individual beds, the degree of spatial heterogeneity (or ‘‘patchiness’’), and other meso-scale variables, appear to have effects, as do micro-scale variables such as shoot density (Jackson et al., 2001). Seagrass beds exist naturally as vegeta- tional units of various shapes and sizes, or have unvegetated or macroalgal regions interspersed among more homogenous seagrass areas (Robbins and Bell, 1994). These patterns are not necessarily the result of human perturbations, and are at- tributable to a host of factors (see review by Bostro ¨m et al., this issue). Jersey’s physical setting and varied coastline, * Corresponding author. E-mail address: emma.jackson@plymouth.ac.uk (E.L. Jackson). 0272-7714/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.ecss.2006.01.024 Estuarine, Coastal and Shelf Science 68 (2006) 421e432 www.elsevier.com/locate/ecss