377 INTEGR.COMP.BIOL., 45:377–385 (2005) Biodiversity, molecular ecology and phylogeography of marine sponges: patterns, implications and outlooks 1 GERT WO ¨ RHEIDE, 2, *² A NTONIO M. SOLE ´ -CAVA,² AND JOHN N. A. HOOPER‡ *Geowissenschaftliches Zentrum der Universita ¨t Go ¨ttingen, Abt. Geobiologie, Goldschmidtstr. 3, D-37077 Go ¨ttingen, Germany ² Depto Gene ´tica, Instituto de Biologia, Universidade Federal do Rio de Janeiro, Ilha do Funda ˜o, 21941-490-Rio de Janeiro, Brazil ‡Queensland Centre for Biodiversity, Queensland Museum, Grey Street, South Brisbane QLD 4101, Australia SYNOPSIS. Marine sponges are an ecologically important and highly diverse component of marine benthic communities, found in all the world’s oceans, at all depths. Although their commercial potential and evo- lutionary importance is increasingly recognized, many pivotal aspects of their basic biology remain enig- matic. Knowledge of historical biogeographic affinities and biodiversity patterns is rudimentary, and there are still few data about genetic variation among sponge populations and spatial patterns of this variation. Biodiversity analyses of tropical Australasian sponges revealed spatial trends not universally reflected in the distributions of other marine phyla within the Indo-West Pacific region. At smaller spatial scales sponges frequently form heterogeneous, spatially patchy assemblages, with some empirical evidence suggesting that environmental variables such as light and/or turbidity strongly contribute to local distributions. There are no apparent latitudinal diversity gradients at larger spatial scales but stochastic processes, such as changing current patterns, the presence or absence of major carbonate platforms and historical biogeography, may determine modern day distributions. Studies on Caribbean oceanic reefs have revealed similar patterns, only weakly correlated with environmental factors. However, several questions remain where molecular ap- proaches promise great potential, e.g., concerning connectivity and biogeographic relationships. Studies to date have helped to reveal that sponge populations are genetically highly structured and that historical processes might play an important role in determining such structure. Increasingly sophisticated molecular tools are now being applied, with results contributing significantly to a better understanding of poriferan microevolutionary processes and molecular ecology. INTRODUCTION Molecular studies in marine biodiversity and ecol- ogy have enjoyed a steady boost in popularity since the mid-1980s. Applying increasingly sophisticated molecular tools (e.g., Sunnucks, 2000; Posada and Crandall, 2001), these studies have contributed much to better understanding the marine biome. The ocean has been thought to have few boundaries, and marine species have been often perceived to be panmictic (Palumbi, 1994). However, genetic studies have clearly shown that this is mostly not the case, with frequent occurrence of cryptic sibling species (Thorpe and Sole ´-Cava, 1994; Knowlton, 2000). Furthermore, ge- netic markers have allowed determination of ranges and distributions of marine taxa, and estimation of ge- netic diversity of marine stocks. Molecular markers have also made it possible to evaluate the degree of genetic cohesiveness between populations of marine species, as well as discrimination of the ecological and historical processes shaping their present day distri- butions. Genetic studies of this kind are pivotal aids to bioregional planning, fisheries management and conservation of dwindling marine resources. Marine sponges are an essential and highly diverse component of marine benthic communities, ranging from the euryhaline estuarine, to intertidal, to the deep-sea (Hooper and Van Soest, 2002). Aside from 1 From the Symposium Sponges: New Views of Old Animals pre- sented at the Annual Meeting of the Society for Integrative and Comparative Biology, 5–9 January 2004, at New Orleans, Louisiana. 2 E-mail: gert.woerheide@geo.uni-goettingen.de their important role for reconstructing metazoan evo- lutionary relationships (e.g., see Maldonado, 2004; Nichols, 2004), the commercial potential of sponges is increasingly being recognized (e.g., Munro et al., 1994; Faulkner, 2002), but many aspects of their basic biology and especially their biogeographic relation- ships remain enigmatic. Some recent major changes were proposed for the higher systematics of Porifera (Hooper and Van Soest, 2002) and molecular data have significantly contrib- uted to our understanding of sponge systematics (re- viewed in Borchiellini et al., 2000; Boury-Esnault and Sole ´-Cava, 2004). Despite significant progress towards the goal of a strictly phylogenetic classification of all sponge classes corroborated by robust molecular data (e.g., Chombard et al., 1997; Alvarez et al., 2000; Mc- Cormack et al., 2002; Manuel et al., 2003; Erpenbeck, 2004), the systematic framework in general is still rel- atively poorly resolved. Similarly, knowledge of bio- diversity (richness, endemism, spatial distributions, e.g., Hooper et al., 2002), historical biogeographic af- finities (e.g., van Soest and Hajdu, 1997) remains ru- dimentary and there are few data about genetic vari- ation among sponge populations and spatial patterns of this variation (reviewed in van Oppen et al., 2002b; Boury-Esnault and Sole ´-Cava, 2004). Even less is known about the processes responsible for shaping the genetic structure of sponge populations (Wo ¨rheide et al., 2004c). Better understanding of these aspects has crucial im- plications for evolutionary and ecological studies not only of sponges, but of most marine invertebrate spe- Downloaded from https://academic.oup.com/icb/article/45/2/377/778555 by guest on 09 April 2023