Induction of settlement and metamorphosis in larvae of Aplysia brasiliana and Strombus gigas (Mollusca: Gastropoda)

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)


Marine Biology and Fisheries

First Committee Member

Harding B. Michel, Committee Chair

Second Committee Member

Scott E. Siddall, Committee Member


Aplysia brasiliana larvae exhibited substrate-specificity during settlement and metamorphosis on red algae. Strombus gigas larvae were less discriminating, metamorphosing on all algal species tested. Of nine species of red algae tested, Laurencia obtusa induced the highest percentage of larvae of A. brasiliana and S. gigas. A. brasiliana larvae possess the capability to prolong metamorphic competence for a period up to 150 days during which spontaneous metamorphosis never occurred. The requirement of A. brasiliana for specific algal species is virtually absolute. S. gigas retained metamorphic competence for only three to four days.Both A. brasiliana and S. gigas larvae discarded cilia in response to the crude seawater extract of L. obtusa. In competent S. gigas larvae, response analyses predicted maximum response (discarding of velar cilia) at 3.1 h and at a concentration of 13.4 $\mu$g of algal protein per ml of seawater, whereas A. brasiliana larvae, was 27 h and 93.4 $\mu$g of algal protein per ml of seawater. S. gigas larvae completed metamorphosis within 20 h after a maximum of 4 h of exposure to the crude extract of L. obtusa. A. brasiliana, apart from discarding of velar cilia, showed no further progress toward completion of metamorphosis.Epiphytes on L. obtusa might effect metamorphosis of both A. brasiliana and S. gigas. Scanning electron microscopy suggested that crude algal extract and the substrate acted in combination to promote completion of metamorphosis. In A. brasiliana, epiphytic films alone failed to support completion of metamorphosis.The spectroscopic properties of L. obtusa indicated that pigments of crude extract consisted mainly of R-phycoerythrin but that R-phycocyanin and allophycocyanin were also present in minor quantities. It is hypothesized that red algal pigments (phycobiliproteins) in the crude algal extract was an inducer. Phycobilisomes (PBSs), the supramolecular assemblies of phycobiliproteins and linker proteins, were isolated from L. obtusa. The positions of maximum and minimum peaks in the absorption spectra of PBSs and dissociated PBSs coincided with those of crude extract of L. obtusa. Dissociated PBS, which mainly consists of phycoerythrin, induces metamorphosis of S. gigas larvae. (Abstract shortened with permission of author.)


Biology, Oceanography

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