Contributions to Zoology, 76 (2) 121-142 (2007) Sponge diversity and community composition in Irish bathyal coral reefs Rob W.M. van Soest1, Daniel F.R. Cleary1,2, Mario J. de Kluijver1, Marc S.S. Lavaleye3, Connie Maier3, Fleur C. van Duyl3 1Zoological Museum of the University of Amsterdam, P.O. Box 94766, 1090 GT Amsterdam, the Netherlands, soest@ science.uva.nl; 2Institute for Biodiversity and Ecosystem Dynamics, Faculty of Science, University of Amsterdam, P.O. Box 94766, 1090 GT, Amsterdam, the Netherlands, [email protected]; 3Royal Netherlands Institute for Sea Research, P.O. Box 59, 1790 AB Den Burg, Texel, the Netherlands, [email protected] Key words: coldwater, multivariate analysis, North Atlantic, ordination, PCA, Porifera, RDA Abstract west of Ireland were found to have a combined sponge species richness of 191 species, exceeding the richness of individual reef Sponge diversity and community composition in bathyal cold mound areas by c. 38-45%. Sponge presence in CWRs is water coral reefs (CWRs) were examined at 500-900 m depth clearly structured and controlled by biotic and abiotic factors. on the southeastern slopes of Rockall Bank and the northwestern In particular, live coral presence appears a signifi cant predictor slope of Porcupine Bank, to the west of Ireland in 2004 and 2005 of CWR sponge composition and diversity. with boxcores. A total of 104 boxcore samples, supplemented with 10 trawl/dredge attempts, were analyzed for the presence and abundance of sponges, using microscopical examination of Contents (sub)samples of collected coral branches, and semi-quantitative macroscopic examination. Approximate minimum size of iden- Introduction .................................................................................... 121 tifi ed and counted sponge individuals was 1 mm. Literature data Materials and methods ................................................................. 123 were added to the Porcupine Bank results to compensate for a Study areas ............................................................................... 124 less intensive sampling program in that location. Species richness Sponge identifi cation ............................................................. 128 and abundance were determined at local (sample diversity, Analysis .......................................................................................... 129 pooled-sample diversity, local reef diversity), between-reef Species richness ...................................................................... 129 (diversity of two reef areas at 15 km distance), and regional Ordination and Permanova ................................................... 132 scales (diversity of three reef areas over a distance of 200 km). Cluster analysis ....................................................................... 133 Abiotic and biotic parameters including depth, the presence and Results ............................................................................................. 133 cover of live coral, dead coral and sand, local reef, and orienta- Coldwater reef sponges from the region W of Ireland ... 133 tion towards the nearest reef mound summit, were included in a Species richness ...................................................................... 133 constrained ordination technique (RDA); a Monte Carlo forward Community composition ....................................................... 134 selection procedure was used to obtain signifi cant predictors of Reef / non-reef diversity ........................................................ 137 variation in composition. The results of this analysis were com- Growth forms ........................................................................... 138 pared with unconstrained ordination (PCA) and cluster analysis. Discussion ...................................................................................... 139 The presence of live coral, depth and the local reefs C1 and C3 Presence of live coral and occurrence of sponge species ... 139 proved to be signifi cant predictors of variation in sponge com- Species composition and habitat ......................................... 139 position. The PCA and cluster analysis confi rmed these results. Growth forms ........................................................................... 139 Sample species richness was consistently heterogeneous from Species richness of shallow-water reefs and CWRs ....... 140 zero species and individuals up to 57 species and 90 individuals Sampling gear .......................................................................... 140 per (boxcore) sample. Species richness of local reefs determined Sample size .............................................................................. 140 from pooled samples showed the three localities studied to have Acknowledgements ...................................................................... 140 similar species richness, namely 105-122 species in each location. References ...................................................................................... 140 Species richness was highest in samples with relatively low live coral cover. As in the RDA, live coral presence and depth ap- peared to be responsible for most of the variation observed in Introduction the cluster results. Cluster analysis of Bray-Curtis dissimilarity values of the pooled samples of all three reef localities using presence / absence data of all available samples indicated that Northwestern European continental slopes and oceanic distance appeared to structure the composition of the sponge banks/seamounts contain extensive coral reef forma- assemblages of the three reef mound areas, but much less so tions at depths of 200-1200 m (Freiwald and Roberts, within and among local reefs. Bathyal reefs of the regions to the 2005). Reefs are predominantly built by two scleractin- 122 R.W.M. van Soest et al. – Sponge diversity in Irish bathyal coral reefs ian coral species, Lophelia pertusa and Madrepora However, current directions in the Eastern North Atlan- oculata (with Stylaster gemmascens as an additional tic (Bersch, 1995) are a complicated interplay of (1) structural species). Elsewhere in the world, in similar eastward directed surface currents, (2) northward di- environments, similar reefs exist consisting of the same rected intermediate and bottomwater currents, as well or a few other species. The paucity of reef-building as - in the northern North Atlantic and more to the west species in these coldwater reefs (CWRs) contrasts with - (3) southward directed currents, and (4) strong re- high biodiversity and great abundance of suspension sidual tidal currents (White et al., 2005). Also, larval feeders, grazers, scavengers and predators (Jensen and dispersal capabilities of reef organisms may be limited Frederiksen, 1992), even rivaling tropical shallow wa- to scales of 10-100 km, even in groups that developed ter reef communities in faunal diversity. long-distance (teleplanic) larvae, as has been established The size and frequency of occurrence of these reef for shallow-reef fi shes (Cowen et al., 2006). communities along the European coasts have previ- The present study focuses on sponges, rather than on ously been reported (e.g. Broch, 1922; Dons, 1944), but an integral community approach (Jensen and Frederik- were largely ignored, until Wilson (1979) ‘rediscovered’ sen, 1992; Mortensen and Fosså, 2006). Often integral them. Since then, mapping of CWRs has received un- community approaches focus on well-known taxa and precedented attention from geologists and biologists. It fail to adequately resolve lesser-known taxa. Mortensen appears that size and frequency increase from south to and Fosså’s (2006) comprehensive study of the species north along the continental margins of Europe, with the diversity and spatial distribution of invertebrates in most extensive reefs reported from areas to the south Norwegian CWRs is a case in point; they mention the and west of Ireland (De Mol et al., 2002), off north- occurrence of 16 sponge species of which 5 were only western Scotland (Roberts et al., 2000), the Far Oer identifi ed to higher taxon, whereas a conservative esti- (Bruntse and Tendal, 2001) and along the continental mate predicts that there may be 5 to 10 times more slope of Norway (Broch, 1922; Dons, 1944; Fosså et al., species in these reefs. Statements about numerical rich- 2005). Southwards, along the coasts of France, the Ibe- ness and abundance of various invertebrate groups made rian peninsula, and in the Mediterranean coral reefs are by these authors cannot be taken as defi nitive in view apparently only present in smaller formations (e.g. of their disregard for the true sponge diversity of Nor- Duineveld et al., 2004; Alvarez-Perez et al., 2005; Ta- wegian reefs. viani et al., 2005), but there is ample evidence for the Sponge diversity in tropical shallow-water coral reefs existence of extensive reef formations of Pleistocene has been the subject of a considerable body of literature and early Holocene age in these areas (De Mol et al., (see e.g. Hooper and Kennedy, 2002; Hooper et al., 2005). This is consistent with a scenario of Holocene 2002; Cleary et al., 2005; Becking et al., 2006; De northward extension of previously Mediterranean-At- Voogd et al., 2006), in which estimates of local reef and lantic CWRs, with concurrent extinction and dying off regional diversity are presented, and attempts at explain- of reefs in the south. Possibly, this scenario is a repetition ing