Original article Can land crabs be used as a rapid ecosystem evaluation tool? A test using distribution and abundance of several genera from the Seychelles Sarah Brook a, * , Alastair Grant b , Diana Bell a a School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, UK b School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK article info Article history: Received 17 September 2007 Accepted 7 July 2009 Published online 31 July 2009 Keywords: Coenobita Exotic vegetation Habitat quality Island ecosystems Ocypode abstract Habitat destruction and the introduction of exotic species are the primary causes of biodiversity loss in tropical island ecosystems. Conservation efforts on oceanic islands are often biased towards charismatic vertebrate faunas, neglecting invertebrate assemblages. We sampled the land crab community on five islands in the central Seychelles; in the intertidal zone, in the supralittoral zone and in nine different inland habitat types to explore the impacts of exotic vegetation and environmental variables on land crab abundance and community composition, and investigate whether land crabs can be used as a tool for the rapid assessment of habitat quality on tropical oceanic islands. We found that species richness and the abundance of the dominant ghost crab Ocypode cordimana was higher in native habitat types than habitats dominated by exotic vegetation. Available ground substrate suitable for burrowing may be a limiting factor for O. cordimana in exotic habitat types. Coenobita rugosus, the dominant crab in the supralittoral zone is largely absent where there is no supralittoral vegetation. These results suggest that land crabs could be reliable indicators of habitat quality on oceanic islands. The abundance of land crabs could be used in the rapid assessment of ecosystem perturbation and identification of sites requiring restoration or management. Ó 2009 Elsevier Masson SAS. All rights reserved. 1. Introduction Oceanic islands are often priorities for conservation action owing to their high levels of endemism and continuing loss of habitats and species following anthropogenic activities (Myers et al., 2000). Habitat modification together with introductions of exotic species, are the primary threats to island biodiversity and indeed many other ecosystems (Brooks et al., 2002). These factors have, for example, contributed to the loss of more than 80 species of endemic land birds in Hawaii since human colonisation (Steadman, 1995), the high percentage (61%) of non-indigenous vascular plants in the Azorean archipelago (Silva and Smith, 2004) and the loss of over 40 percent of New Zealand’s avifauna (Dowding and Murphy, 2001). On island archipelagos and many other ecosystems, conservation efforts have focused largely on the endemic avifauna and large land vertebrates. The diverse Seychelles archipelago contains the only granitic islands in the Indian Ocean. These islands have been classified as a conservation priority owing to their high proportion of endemic taxa, many of which are threatened with extinction (Burgess et al., 2006). Extensive lowland forest clearance for agriculture since the 18th century has resulted in the extinction of at least three endemic bird species, localised extinctions of populations from many islands (Diamond, 1984) and the dominance of introduced plants in many habitats (Gerlach, 1993; Fleischmann, 1999). The restoration of native ecosystems, in conjunction with the eradication of invasive species is crucial to the conservation of island flora and fauna (Thorsen et al., 2000). Restoration programmes tend to be very costly however, depending on the interventions needed to reha- bilitate degraded ecosystems. Field surveys represent the most significant cost in planning the restoration of island ecosystems in the Seychelles, accounting for approximately 15% of the total esti- mated cost of restoration programmes. Average survey costs across 11 potential islands was estimated at US $155 per ha (Henri et al., 2004). These costs could be reduced however, by the development of a method for rapid assessment of ecosystem state. The extent to which invasive species and the associated changes to ecosystem structure has affected lesser known native species in the Seychelles has not been quantified. The impact of an infestation of the yellow crazy ant (Anoplolepsis gracilipes) on the community composition of ground-dwelling invertebrates on Bird Island, Seychelles, in 2000 highlighted the potential effects of invasive species on invertebrate populations. Larger decapod crustaceans were almost eliminated from the worst affected areas, with * Corresponding author. Tel.: þ44 84 1683 344057; fax: þ44 84 43719 3049. E-mail address: sbrooky2@hotmail.com (S. Brook). Contents lists available at ScienceDirect Acta Oecologica journal homepage: www.elsevier.com/locate/actoec 1146-609X/$ – see front matter Ó 2009 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.actao.2009.07.001 Acta Oecologica 35 (2009) 711–719