Recruitment and metamorphosis of Haliotis larvae induced by molecules uniquely available at the surfaces of crustose red algae

Abstract

Crustose red algae induce substratum-specific settlement, attachment and metamorphosis of the planktonic larvae of Haliotis rufescens Swainson (gastropod mollusc), upon direct contact by the larvae with any of a number of algal species tested. Larvae are not induced by contact with intact foliose red, brown or green macroalgae. Geniculate red algae are only slightly active. Larval settlement and metamorphosis are shown to be triggered by a class of chemical inducers associated with macromolecules and found in extracts of all species of crustose, geniculate, and foliose red algae tested; these inducers are not found in extracts of brown or green macroalgae. The substratum specificity of larval settlement and metamorphosis is shown to result from the unique availability of these inducers at the surfaces of the crustose red algae. Using a newly-developed improved method of purification based upon size-separation by gel-filtration, followed by ion-exchange chromatography over a diethylaminoethyl (DEAE)-acrylamide matrix, the principal inducer of Haliotis larval settlement and metamorphosis has been resolved from the red algal phycobiliproteins. Sensitivity of this inducer to reduction in molecular weight by digestion with trypsin demonstrates that this inducer is associated with protein.