Effects of body size, water current and microhabitat on mucous-thread drifting in post-metamorphic gastropods Lacuna spp.

The behaviour of snails was studied using a miniature flow tank mounted on a stereomicroscope equipped with a video camera.For Lacuna vincta, juveniles (ca 5 3 mm shell length) displayed foot-raising behaviour and initiated drifting in less time than adults (ca 23.5 to 4 mm).In contrast, there was no difference in juvenile and adult responses in L. variegata.When exposed to water current, individuals of both species usually displayed foot-raising behaviour, which was usually followed by mucous-thread dnfting.Both oscillatory (8 to 9 s cycle-') and unidirectional water currents triggered foot-raising and drifting (peak water velocity: 15 to 17 cm S-').Compared with individuals maintained in favourable microhabitats (dishes containing some of the algae from which they were originally collected in the field), the likelihood of foot-raising and drifting was 3 to 5 times higher in juveniles maintained in unfavourable rnicrohabitats before the experiment (24 h in dishes containing no algae on which to crawl and feed).In the field, unfavourable microhabitats, those lacking proper algal substrate or shelter, may increase the likelihood, of post-metamorphic dispersal by triggering mucous-thread drifting by water current.