Abstract
Tadpole larvae of the solitary ascidian Molgula citrina Alder & Hancock were examined in behavioral and settlement bioassays to test their reactions to several physical and biotic cues known to influence habitat choice in larvae of other ascidian species. These assays revealed that M. citrina larvae, though previously reported to lack photoreception, are nonetheless strongly influenced by lighting cues when sampling potential substrata. Larval responses to other settling larvae, adult conspecifics, a congener, and an heterospecific superior competitor were also tested. Larvae settled randomly with respect to each other both in the dark and under ambient light conditions, suggesting that the gregarious settlement exhibited by larvae of many benthic invertebrates does not occur in this species. In bioassays testing the metamorphosis-inducing potential of homogenized tunic from adult ascidians, M. citrina larvae responded differentially to the three ascidian species examined. Percent metamorphosis in a population of M. citrina larvae decreased when exposed to conspecific tunic material, but increased in the presence of tunic homogenate from the heterospecific competitor. Settlement responses of M. citrina larvae to light cues and to water-borne chemicals may influence adult distributions in this ascidian species.
Published Version
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