Research Director: Dr. Nobuhiro Fusetani
(Professor, Faculty of Agriculture, The University of Tokyo)
Research Term: 1991～1996

This project focused on larval settlement and metamorphosis, extremely important components in understanding the interactions between marine organisms. The functions of chemical substances were investigated concerning both the receptors and second messengers as parts of these particular phenomena. Specifically, the project searched for settlement-inducing and -inhibiting compounds from various sources. It also investigated the expression of the function mediated by second messengers.

Research Results

Larval culture of sessile marine organisms: Larval culture techniques were established for the mussel Mytilus edulis galloprovincialis, two barnacles Balanus amphitrite and Megabalanus rosa, the hydroid Tubularia mesembryanthemum, and the bryozoan Bugula neritina.

Imaging analysis of larval behaviors during settlement: A calcium imaging system was developed to track the calcium concentrations within the larval body.

Chemical cue to settlement in barnacles: A large (>200 kDa) settlement-inducing protein complex (SIPC) was isolated from adult barnacles comprising sugar chains. It has also been clarified that SIPC is synthesized during larval development, and is probably involved in both adult-larva and inter-larval interactions.

Signal-transduction systems and cementing in barnacle larvae: Following the reception of chemical cue(s), larvae experience an internal signal for attachment, which is believed to pass through the nervous system to release cementing substances, which solidify once released into the surrounding seawater. On the other hand, metamorphosis is controlled secondarily via the hormonal activation of enzymes.

Antifouling compounds against barnacle larvae: More than 300 marine invertebrates were screened for antifouling activity, and more than 60 antifouling compounds obtained. Some of them showed strong antifouling activity without toxicity at very low concentrations.

Exogenous/endogenous factors for settlement of actinula larvae: The discharge of nematocysts leading to cement secretion and body-pattern transformation has been discovered to be involved in the settlement of actinulae. Also, an influx of calcium ions and diatoms may play important roles in mechano/chemo-reception for nematocyst discharge.

Characterization of bryozoan larvae: The involvement of catecholamines, serotonin and acetylcholine in various aspects of larval behavior through the nervous system was uncovered with whole larvae as well as single cells of which dissociation and culture were newly established.

Metamorphosis-inducing substances of ascidian larvae: Together with metamorphosis-inducers from various marine organisms, the real cue to metamorphosis has been isolated from conspecific conditioned water, and identified as lumichrome. It was also found that some metal ions and metalloproteinases play very important roles during the metamorphosis of ascidians.

Microbial films: The growth of microbial films in the field has been examined in detail. Facilitating effect of these films on larval settlement of barnacles could be correlated with volume (thickness) of films.

·Life Cycle of Barnacle

·Marine Hydrozoan Tubularia mesembryanthemum A:Polyp(male) B:Polyp(female) C:Actinula larva