title: Resilience to disturbance despite limited dispersal and self-recruitment in tropical barrel sponges: implications for conservation and management.
abstract: While estimates of connectivity are important for effective management, few such estimates are available for reef invertebrates other than for corals. Barrel sponges are one of the largest and most conspicuous members of the coral reef fauna across the Indo-Pacific and given their large size, longevity and ability to process large volumes of water, they have a major role in reef functioning. Here we used a panel of microsatellite markers to characterise the genetic structure of two barrel sponge species, Xestospongia testudinaria and a currently undescribed Xestospongia species. We sampled across seven populations in the Wakatobi Marine National Park, SE Sulawesi (Indonesia) spanning a spatial scale of approximately 2 to 70 km, and present the first estimates of demographic connectivity for coral reef sponges. Genetic analyses showed high levels of genetic differentiation between all populations for both species, but contrasting patterns of genetic structuring for the two species. Autocorrelation analyses showed the likely dispersal distances of both species to be in the order of 60 and 140 m for Xestopongia sp. and Xestospongia testudinaria, respectively, which was supported by assignment tests that showed high levels of self-recruitment (>80%). We also found consistently high inbreeding coefficients across all populations for both species. Our study highlights the potential susceptibility of barrel sponges to environmental perturbations because they are generally long-lived, slow growing, have small population sizes and are likely to be reliant on self-recruitment. Surprisingly, despite these features we actually found the highest abundance of both barrel sponge species (although they were generally smaller) at a site that has been severely impacted by humans over the last fifty years. This suggests that barrel sponges exhibit environmental adaptation to declining environmental quality and has important implications for the management and conservation of these important reef species.
authors.affiliation: School of Biological Sciences, Victoria University of Wellington, Wellington, New Zealand.
authors.forename: James J
authors.initials: JJ
authors.lastname: Bell
authors.affiliation: Coral Reef Research Unit, University of Essex, Colchester, United Kingdom.
authors.forename: David
authors.initials: D
authors.lastname: Smith
authors.affiliation: School of Biological Sciences, Victoria University of Wellington, Wellington, New Zealand.
authors.forename: Danielle
authors.initials: D
authors.lastname: Hannan
authors.affiliation: Research and Development Center on Marine, Coastal and Small Islands, Hasanuddin University, Makassar, Indonesia.
authors.forename: Abdul
authors.initials: A
authors.lastname: Haris
authors.affiliation: Research and Development Center on Marine, Coastal and Small Islands, Hasanuddin University, Makassar, Indonesia.
authors.forename: Jamaludin
authors.initials: J
authors.lastname: Jompa
authors.affiliation: The Oceans Institute, School of Plant Biology, University of Western Australia, Australia.
authors.forename: Luke
authors.initials: L
authors.lastname: Thomas
mesh_terms: D000483:Alleles; D063147:Animal Distribution / Q000502:physiology*; D000818:Animals; D001499:Bayes Theorem; D049628:Body Size; D016000:Cluster Analysis; D016001:Confidence Intervals; D003247:Conservation of Natural Resources; D014644:Genetic Variation; D005828:Genetics, Population; D005843:Geography; D007214:Indonesia; D018895:Microsatellite Repeats / Q000235:genetics; D025341:Principal Component Analysis; D014329:Tropical Climate; D047131:Xestospongia / Q000235:genetics / Q000502:physiology*