BEHAVIORAL-RESPONSES OF CONCHOLEPAS-CONCHOLEPAS (BRUGUIERE, 1789) LARVAE TO NATURAL AND ARTIFICIAL SETTLEMENT CUES AND MICROBIAL FILMS

The behavioral responses of veliger larvae of the gastropod Concholepa s concholepas were studied in the presence of different natural and ar tificial settlement cues and microbial films. Early pre-competent larv ae stopped swimming, sank (due to ciliary arrests, retraction of the v elum into the shell, or both), and remained inactive on the substratum when exposed to conspecific mucus and hemolymph. In both cases the ef fect was time-dependent and the number of larvae showing these behavio rs decreased over time. Larvae exposed to NH4Cl (ammonium ion) showed a similar time- and dose-dependent response. A positive and time-depen dent response was also observed when larvae were exposed to different extracellular matrix (ECM) components (i.e., collagen, gelatin, and fi bronectin) and sulfated polysaccharides (i.e., carrageenan, heparin, a nd chondroitin sulfate). In this case the larvae remained attached to the substratum. However, the effect of sulfated polysaccharides on C. concholepas larval behavior was faster than that observed with other E CM molecules. We also studied the responses of premetamorphic C. conch olepas larvae exposed to different microbial films. In chemotaxis expe riments with different films, with glass as the substratum, larvae sho wed a significant preference for multispecific and diatoms films. When shells of C. concholepas were used as the substratum, the preference for multispecific films was clear and significant, Likewise, larvae sh owed velar contractions in the presence of all the films tested. Larva e exposed to multispecific films and to the microalga Prasinocladus ma rinus showed an increased ciliar movement. The finding that mucus and hemolymph of conspecific adults and ECM molecules (mainly sulfated pol ysaccharides) induce the cessation of swimming of C. concholepas larva e suggests a possible role for cell-surface receptors in mediating the larval response of marine organisms. Likewise, the positive chemotaxi s responses of C. concholepas larvae to different microbial films sugg est that microorganisms may have a role in bringing larvae close to se ttlement inducers on the marine benthos.