MICRODISTRIBUTION IN THE FIELD AND HABITAT CHOICE IN AQUARIA BY COLOUR MORPHS OF LITTORINA MARIAE SACCHI & RASTELLI

The microdistributions of yellow and brown morphs of adult andjuvenile Littorina mariae were investigated in the field onFucus plants. On F. vesiculosus in autumn, yellow adults werefound more frequently than expected on laminae and brown adultsmore frequently than expected on stipes. In spring there wasno difference in distribution between adult morphs. There wasno difference in microdistribution betweenjuvenile morphs oneither F. vesiculosus or F. serratus in autumn. Yellow and brown adults were allowed to choose between an artificialbrown and an artificial yellow background, and between stipeand lamina of F. serratus in aquarium experiments. Both morphspreferred the yellow rather than the brown background. In mostcases, the morphs climbed upwards on F. serratus, regardlessof algal orientation (lamina upwards or stipe upwards) or lightregime (lights on or off). A significant difference in microdistributionbetween morphs was found with the lamina placed upwards andthe lights on. Brown snails then preferred stipe, while yellowsnails did not show a preference for either stipe or lamina. (Received 16 June 1994; accepted 31 October 1994)