Larval settlement to conspecific cues for the Indo Pacific sponge Luffariella variabilis

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For sessile marine invertebrates, larval behaviours that contribute to settlement in close proximity to conspecifics can enhance post-settlement success and recruitment to populations. Conspecific settlement is documented in several groups of sessile invertebrates, but this process is conspicuously absent for sponges. We used conspecific-derived cues from the tropical Indo-Pacific sponge, Luffariella variabilis, to establish the influence of larval settlement to conspecifics. Here, we tested larval-conditioned water (including polar and non-polar fractionations thereof), extract of adult sponge tissue and the abundant secondary sponge metabolite, manoalide monoacetate, in a series of larval settlement assays, repeated over three independent spawning years. There was a significant association between time to settlement and conspecific cues; larval settlement was completed within half a day in the presence of conspecific cues compared to no settlement in control treatments, (i.e. with no cue). Only after 2 days did larvae in control treatments display similar levels of mean larval settlement (80 ± 20%), highlighting that settlement is accelerated by exposure to conspecific cues. Larvae exhibited a preference for, and settled at significantly higher rates in the presence of, relatively non-polar secondary metabolites concentrated from larval-conditioned water than for polar compounds or the control.