RESEARCH ARTICLE S. Whalan Æ M. S. Johnson Æ E. Harvey Æ C. Battershill Mode of reproduction, recruitment, and genetic subdivision in the brooding sponge Haliclona sp. Received: 31 January 2004 / Accepted: 23 August 2004 / Published online: 28 September 2004 Ó Springer-Verlag 2004 Abstract Sponges display a variety of reproductive strategies that have the potential to influence popula- tion genetic structure. Histological examination of ten reproductive individuals of the Western Australian sponge Haliclona sp. showed that this species broods embryonic larvae that are potentially limited in dis- persal capabilities. Because sponges have the potential to propagate in a number of modes, allozyme elec- trophoresis was used to assess the relative importance of asexual and sexual reproduction to recruitment, and to quantify genetic subdivision over different spatial scales. Tissue samples from 227 sponges were collected from reefs within two areas 400 km apart: Hamelin Bay and Rottnest Island. Contrary to expectations for highly clonal populations, genotypic diversity within sites was high, no linkage disequilibrium was found, and there was no evidence of genotypic clustering within reefs. There was no genetic evidence that asexual reproduction is important for the maintenance of populations. Genetic comparisons were consistent with mixing of sexually produced recruits within reefs, on a scale up to a few hundred metres, but significant genetic subdivision between reefs (F ST =0.069 at Ha- melin Bay, 0.130 at Rottnest Island) indicated that water gaps of several hundred metres are effective at preventing dispersal. Subdivision between the two areas, separated by 400 km, was moderately greater (F ST =0.142) than within, but the same alleles were predominant in the two areas. These genetic patterns are consistent with limited dispersal capabilities of brooded larvae. Introduction Understanding patterns of population genetic structure for sessile marine invertebrates can be complicated by the influences of dynamic life-history traits. Diversity in modes of reproduction, sexuality, and larval develop- ment for many species in this group can promote complex patterns in population genetic structures. For a large number of sessile marine taxa, genetic variation of local populations can be reduced by clonal repro- duction (e.g. Ayre 1984; Stoddart 1984) or localised recruitment of larvae with restricted dispersal capabili- ties (e.g. McFadden 1997; Ayre and Hughes 2000). Across broader spatial scales connectivity between sessile marine invertebrate populations is mediated by mobile larval phases; however, larval dispersal potential can be influenced by a combination of factors (Palumbi 1994), including mode of larval development (Jackson 1986). The influence of mode of larval development on dispersal potential and genetic structure is well docu- mented. Planktotrophic larvae, resulting from broad- cast spawning, are often in the water column from days to weeks, which can result in panmictic popula- tion structure (e.g. Williams and Benzie 1993; Hellberg 1996). In comparison, brooding species often produce well-developed larvae competent to settle in substan- tially less time, resulting in higher levels of popula- tion subdivision (e.g. McFadden 1997; Bastidas et al. 2002). Sponges are one group of sessile invertebrates that show a broad range of reproductive strategies, including Communicated by G.F. Humphrey, Sydney S. Whalan (&) Æ M. S. Johnson Æ E. Harvey Faculty of Natural and Agricultural Science, University of Western Australia, 35 Stirling Highway, 6009 Crawley, WA, Australia E-mail: stephen.whalan@jcu.edu.au C. Battershill Australian Institute of Marine Science, PMB 3, 4801 Townsville, QLD, Australia Present address: S. Whalan School of Marine Biology and Aquaculture, James Cook University, 4801 Townsville, QLD, Australia Marine Biology (2005) 146: 425–433 DOI 10.1007/s00227-004-1466-8