ABSTRACT
Abalone shed their gametes into the water column, where fertilization occurs (Seki and Kan-no, 1977). The lecithotrophic laiVae of red abalone develop rapidly, reaching metamoq>hic competency by day seven postfertilization at 152C (D.E. Morse et al., 1979a). Abalone eggs are negatively buoyant (Crofis, 1937; Ino, 1952; Leighton, 1974; Mottet, 1978), and although early laiVae exhibit phototactic behavior (see Mottet, 1978; McShane, 1992), an increasing body of evidence suggests that, for
a substantial portion of development, larvae are likely to be demersal. These data include laboratory observations of behavior of competent larvae in aquaria (Seki and Kan-no, 1977; 1981a,b), recruitment studies in natural environments that indicate that dispersal is limited (Prince et al., 1987, 1988; McShane et al., 1988), and low numbers of larvae found in samples of surface coastal waters (e.g., McShane et al., 1988; and McShane, 1992 for review). However, this larval behavioral characteristic has not been confirmed by direct field observation. Once the developmental stage of competency has been ·reached, larvae respond to particular chemical cues by: (1) ceasing to swim and attaching to the substrate with the foot (setdement), and (2) metamorphosing, the first morphological indicator of which is the shedding of the ciliated cells of the velum, the larval swimming organ. Settlement is a reversible behavioral event that may occur several times prior to metamorphosis. In contrast, metamorphosis is a morphogenetic process that represents an irreversible commitment to a benthic existence. The ability of larvae to respond to chemical substrates has been shown to be contact dependent rather than due to encounters with diffusible cues (D.E. Morse et al., 1980c; Morse and Morse, 1984a).
