Squat Lobster Assemblages on Seamounts Differ from Some, but Not All, Deep-Sea Habitats of Comparable Depth Ashley A
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Marine Ecology. ISSN 0173-9565 ORIGINAL ARTICLE Squat lobster assemblages on seamounts differ from some, but not all, deep-sea habitats of comparable depth Ashley A. Rowden1, Kareen E. Schnabel1, Thomas A. Schlacher2, Enrique Macpherson3, Shane T. Ahyong1 & Bertrand Richer de Forges4 1 National Institute of Water & Atmospheric Research, Wellington, New Zealand 2 Faculty of Science, Health & Education, The University of the Sunshine Coast, Maroochydore DC, Queensland, Australia 3 Centro de Estudios Avanzados de Blanes (CSIC), C. acc. Cala Sant Francesc, Blanes, Girona, Spain 4 Syste´ matique, Adaptation et Evolution, UMR7138UPMC-IRD-MNHN-CNRS (URIRD148), Institut de Recherche pourle De´ velopement, Noume´ a Cedex, Nouvelle-Cale´ donie Keywords Abstract Beta-diversity; community composition; deep- sea; seamounts; squat lobsters. This study was carried out to test the hypothesis that benthic communities on seamounts are distinct from those of other deep-sea habitats at comparable Correspondence depths. Analysis of the squat lobster fauna of deep-sea habitats in the South- Ashley A. Rowden, National Institute of Water western Pacific revealed that the species composition of assemblages on sea- & Atmospheric Research, Private Bag 14-901, mounts was not statistically dissimilar from assemblages on slope and plateau Wellington, New Zealand. habitat at comparable depths. However, compositional differences were E-mail: [email protected] observed between seamount and rise and ridge habitat. Differences in assem- Accepted: 2 April 2010 blage composition between seamount and ridge habitat were statistically signifi- cant for two of the four ridge systems examined. Assemblages on seamounts doi:10.1111/j.1439-0485.2010.00374.x that were distinct from non-seamount ridge habitat were typically dominated by small-bodied species with an abbreviated larval stage. Various environmental variables were correlated with the observed assemblage patterns observed; depth-related variables may account for differences between seamount and rise assemblages, whilst differences in POC flux likely play a role in determining the assemblage compositional patterns between seamount and non-seamount ridge habitat. Extensive pre-analysis data treatment was required to ensure that multivariate analyses of assemblage data from seamount and non-seamount habitats were robust. Our results confirm the findings of recent studies that found no compositional differences in assemblages from seamount and slope habitats, and support the idea that dissimilarity between seamount assemblages on different ridge systems increases with geographic distance. Further research will be required before the generality of these findings can be confirmed. high (Wilson & Kaufman 1987), thereby establishing a Introduction generalization that benthic communities on seamounts Not long after the first detailed geological descriptions of are distinct. This assertion was strongly supported by seamounts (Hess 1946), biologists began to speculate that Richer de Forges et al. (2000), who showed that fish and the composition of biotic communities in such environ- invertebrate communities of seamounts on adjacent ridges ments might differ from other deep-sea habitats (Hubbs in the Southwestern Pacific differed markedly at scales of 1959). Early investigations of benthic assemblages on sea- 1000 km. Since then, researchers have sought to deter- mounts suggested that levels of endemism were relatively mine whether benthic communities on seamounts are Marine Ecology 31 (Suppl. 1) (2010) 63–83 ª 2010 Blackwell Verlag GmbH 63 Squat lobster assemblages of deep-sea habits Rowden, Schnabel, Schlacher, Macpherson, Ahyong & Richer de Forges also dissimilar from other habitats. More recent studies Romero et al. 2004), (v) some species associate closely have examined the species richness, endemism and or with habitat-forming benthic species such as corals (Rice genetic population structure components of communities, & Miller 1991; Kilgour & Shirley 2008), a biogenic habitat rather than overall compositional characteristics, and how that is found on seamounts (Rogers et al. 2007), and (vi) they might differ (i.e. beta-diversity or species turnover) are well-resolved taxonomically. In fact, the Census of among seamounts and other habitats (e.g. Samadi et al. Marine Life project COMARGE (Continental Margin 2006; O’Hara 2007). A few notable exceptions exist. First, Ecosystems) recently produced a world catalogue of spe- Hall-Spencer et al. (2007) found that, on average, the cies (Baba et al. 2008). Finally, in terms of dispersal, composition of coral assemblages on North Atlantic sea- whereas galatheids generally have extended planktotrophic mounts were dissimilar to assemblages on island and larval stages, most chirostylids have an abbreviated larval slope habitats, but that only the taxonomic distinctness of stage, thereby offering a useful contrast in terms of larval coral assemblages on isolated oceanic seamounts and dispersal (Guerao et al. 2006; Clark & Ng 2008). islands was consistently different from the expected taxo- Squat lobster data have recently been compiled for the nomic distinctness of the regional species pool. Secondly, Southwestern Pacific (Schnabel 2009a), covering and O’Hara et al. (2008) found that only ophiuroid assem- extending the region studied by Richer de Forges et al. blages associated with coral matrix on seamounts were (2000) and including data from their analyses (although dissimilar in composition from assemblages not associ- species identifications have been updated). These records ated with biogenic habitat on slope and other seamounts were used to examine the following questions: (i) Are (which were similar to one another) in the Southwestern squat lobster assemblages on seamounts different from Pacific. Finally, McClain et al. (2009) noted that although other habitats at comparable depths? (ii) Do assemblages the epifaunal community on an eastern Pacific seamount on different ridges systems (seamounts and ridge habitat) and a nearby canyon were generally similar in composi- differ? (iii) Do dispersal strategy, body size and environ- tion, there was a difference in the frequency of occurrence mental factors modify spatial patterns in assemblage com- of the component species. position? Although worthy contributions to our understanding of seamount ecology, these recent compositional studies Material and Methods are somewhat equivocal regarding the question of whether benthic communities on seamounts are distinct. Study area What they do demonstrate is that great care is needed The study area is located in the Southwestern Pacific when making comparisons among seamounts, and between 5–60° S and 145° E–170° W, and includes the between seamounts and other habitats. That is, compara- Solomon Islands, Vanuatu, Fiji and Tonga in the north, tive analyses need to take account of the confounding fac- Southeastern Australia in the west, and New Zealand in tors that can plague examinations of data collected from the south (Fig. 1). This area covers a diverse range of sites with different depth ranges, and the combination of undersea geomorphological features, including extensive data from multiple sources where the taxonomic consis- shallow shelf, continental slope, oceanic ridges, rises, tency among datasets may be in doubt. Unfortunately, abyssal basins, troughs, plateaux and seamounts (isolated, the conclusions of the early study of Richer de Forges in complexes, chains, volcanic arcs, or as elevated features et al. (2000) are somewhat confounded by depth (McC- on ridges), which provide habitat for benthic assemblages. lain 2007), and thus the question of whether seamounts on adjacent ridges have distinct benthic communities remains unresolved. Likewise, the difference in assemblage Data composition between seamount and surrounding ridge Data for galatheid and chirostylid squat lobsters were habitats remains completely unassessed. compiled from multiple sources: (i) Historical records for Squat lobsters (decapod families Galatheidae and Chi- global expeditions undertaken by the Challenger, Albatross rostylidae) are particularly well-suited for examining eco- and Galathea, and reports on local collections between logical patterns in the deep-sea. They are (i) relatively 1873 and 1952 (Haswell 1882; Henderson 1888; Faxon large (carapace lengths of 2–70 mm), (ii) easily sampled 1895; Thompson 1899; Baba 1988, 1994, 2005) (67 by gears such as dredges, sleds and trawls, (iii) ubiquitous records). (ii) Collections from the tropical Southwest and common from the continental shelf to the deep-sea Pacific Ocean carried out by the Institute de Recherche (including seamounts), (iv) they display a variety of pour le De´veloppement (IRD) and Muse´um national opportunistic feeding strategies (e.g. suspension- and d’Histoire naturelle, Paris (MnHn), since 1976 (e.g. Saint deposit-feeding, scavenging and predation) (Aurioles- Laurent de & Macpherson 1990; Macpherson 1994, 1996, Gamboa & Pe´rez-Flores 1997; Hudson & Wigham 2003; 64 Marine Ecology 31 (Suppl. 1) (2010) 63–83 ª 2010 Blackwell Verlag GmbH Rowden, Schnabel, Schlacher, Macpherson, Ahyong & Richer de Forges Squat lobster assemblages of deep-sea habits Fig. 1. Map showing the main geomorphic features in Southwestern Pacific Ocean from which squat lobster data were obtained for the study. Dotted lines indicates break between geomorphic features. Bathymetric contours for 200 and 1600 m are shown. Inset: galatheid Munida obesa (left) and chirostylid Uroptychus