Molluskan species richness and endemism on New Caledonian seamounts: Are they enhanced compared to adjacent slopes? Magalie Castelin a,n , Nicolas Puillandre a , Pierre Lozouet b , Alexander Sysoev c , Bertrand Richer de Forges a , Sarah Samadi a a Syste´matique, Adaptation et Evolution, UMR 7138 UPMC-IRD-MNHN-CNRS (UR IRD 148), Muse´um National d’Histoire Naturelle, De ´partement Syste´matique et Evolution, CP 26, 57 Rue Cuvier, F-75231 Paris Cedex 05, France b Direction des Collections, 55 rue Buffon, CP 51, F-75231 Paris Cedex 05, France c Zoological Museum of Moscow State University, Bolshaya Nikitskaya Street 6, Moscow 103009, Russia article info Article history: Received 29 July 2010 Received in revised form 25 March 2011 Accepted 30 March 2011 Available online 13 April 2011 Keywords: Seamount Species richness Diversity Endemism Mollusks Dispersal New Caledonia abstract Seamounts were often considered as ‘hotspots of diversity’ and ‘centers of endemism’, but recently this opinion has been challenged. After 25 years of exploration and the work of numerous taxonomists, the Norfolk Ridge (Southwest Pacific) is probably one of the best-studied seamount chains worldwide. However, even in this intensively explored area, the richness and the geographic patterns of diversity are still poorly characterized. Among the benthic organisms, the post-mortem remains of mollusks can supplement live records to comprehensively document geographical distributions. Moreover, the accretionary growth of mollusk shells informs us about the life span of the pelagic larva. To compare diversity and level of endemism between the Norfolk Ridge seamounts and the continental slopes of New Caledonia we used species occurrence data drawn from (i) the taxonomic literature on mollusks and (ii) a raw dataset of mainly undescribed deep-sea species of the hyperdiverse Turridae. Patterns of endemism and species richness were analyzed through quantitative indices of endemism and species richness estimator metrics. To date, 403 gastropods and bivalves species have been recorded on the Norfolk Ridge seamounts. Of these, at least 38 species ( 10%) are potentially endemic to the seamounts and nearly all of 38 species have protoconchs indicating lecithotrophic larval development. Overall, our results suggest that estimates of species richness and endemism, when sampling effort is taken into account, were not significantly different between slopes and seamounts. By including in our analyses 347 undescribed morphospecies from the Norfolk Ridge, our results also demonstrate the influence of taxonomic bias on our estimates of species richness and endemism. & 2011 Elsevier Ltd. All rights reserved. 1. Introduction Seamounts are often portrayed as hotspots of species richness and centers of endemism (Koslow et al., 2001; Parin et al., 1997; Richer de Forges et al., 2000). To explain these characteristics, it was suggested that barriers to dispersal between seamounts, resulting mainly from landscape fragmentation, could increase local speciation rates (Hubbs, 1959; Mullineaux and Mills, 1997; Richer de Forges et al., 2000). According to this hypothesis, species richness and seamount-scale endemism are expected to increase significantly, particularly in poorly dispersive taxa (Hansen, 1983). Castelin et al. (2010) showed that over the Norfolk Ridge seamounts, in the southwest Pacific, a distance of a few hundreds of kilometers could represent a critical barrier to gene exchanges for species with a short-lived pelagic larva or with direct development. These data revealed cryptic diversity and micro-endemism within studied species. However, the degree to which seamounts are characterized by high endemism and high species richness is still debated and numerous alter- native hypotheses have been proposed (Clark et al., 2010; McClain, 2007; McClain et al., 2009; O’Hara, 2007; O’Hara et al., 2008; Samadi et al., 2006, 2007). At least part of the confusion in these debates follows from the use of the term endemism to refer either to geographical or to ecological patterns. In its geographical sense, a taxon is endemic to an area if it occurs there and nowhere else (Anderson, 1994). In its ecological sense, endemic means confined to a certain habitat characterized by specific environmental conditions (Anderson, 1994). For example, species specialized to hydrothermal vents or cold seeps are often regarded as endemic even if they have a large but fragmented range (e.g. Akiko et al., 2009; Won et al., 2003). In such cases, the term ‘ecological specialization’ may be Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/dsri Deep-Sea Research I 0967-0637/$ - see front matter & 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.dsr.2011.03.008 n Corresponding author. Tel.: þ33 1 40793165; fax: þ33 1 40793844. E-mail address: magcastelin@mnhn.fr (M. Castelin). Deep-Sea Research I 58 (2011) 637–646