Mechanisms of propagule release in the carnivorous sponge Asbestopluma occidentalis

Carnivorous sponges characteristically inhabit the deep sea, so extensive observations of the biology of living specimens are rare. We report on newly discovered shallow-water (<30m depth) populations of the carnivorous sponge Asbestopluma occidentalis and on observations of living adults and larvae from this unique group of sponges. In the Salish Sea, British Columbia, Canada, populations of A. occidentalis exist at depths as shallow as 18m, where they co-occur with hexactinellid sponges. Adults with and without embryos (n=127) were collected and easily maintained in the laboratory for several months, allowing continuous examination of live specimens. Parent sponges naturally disassociated their tissue, facilitating larval release and dispersal. Dispersed larvae had actively beating cilia, but no swimming was observed. Larvae settled and attached from several hours to several days post-release. After larval release, parent sponges reaggregated their disassociated bodies into spherical balls of apparently undifferentiated tissue, which could also disperse and settle. Sexually mature adults were sampled in the field from August to November, with a high proportion of adults containing mature embryos in late November. High-resolution photography and electron microscopy verified that adults were covered with anisochelae spicules, and used these to capture nauplii of Artemia sp. under experimental conditions; however, time-lapse photography showed that some captured prey could free themselves with vigorous swimming. The occurrence of abundant shallow-water populations of A. occidentalis in the Salish Sea provides a rare opportunity to study the evolution and ecology of carnivory in the Porifera.