We collected phytal animals (fauna associated with drifting seaweeds)off the Tohoku coast in northern Japan in May and June 1994 to examine their feeding habits. Phytal animals were assignedto the following three feeding habit groups: (i) carnivores preyingon crustaceans: a gammarid (Stenothoe sp.) and a decapodmegalops; (ii) omnivores feeding on crustaceans and pinnate diatoms:a cirripede (Lepas anserifera), three gammarids (Calliopius sp., Jassaslatteryi and J. marmorata), an isopod (Idotea metallica),a decapod crustacean (Planes cyaneus), a decapod megalopsand two caprellids (Caprella penantis and Caprella mutica);and (iii) herbivores grazing on pinnate diatoms, fucoids and seaweedsother than fucoids: three gammarids (Allorchestes angusta, Amphithoelacertosa and Perampithoe lindbergi), an isopod (Cymodocejaponica) and a polychaete (Platynereis bicanaliculata).Pinnate diatoms in the gut contents were composed mainly of Licmophora spp., Navicula spp., Nitzschia spp.and Cocconeis spp. and seaweeds other than fucoids (i.e. Ectocarpussiliculosus and Sphacelaria furcigera). The latter twoalgae seemed to be epiphytes on drifting seaweeds. These resultssuggest that phytal animals play an important role in drifting seaweed communitiesthrough trophic linkage with two primary producers (i.e. driftingseaweeds and the epiphytes growing on them).

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The age distribution of the sea urchin Strongylocentrotus nudus in relation to algal zonation was studied in a sublittoral rocky area on Oshika Peninsula, northern Japan, from June 1995 through to August 1996. The algal zonation observed there extends from a shallow area of cobbles to deeper areas dominated successively by Sargassum yezoense, Eisenia bicyclis and, finally, crustose coralline red algae. One‐year‐old sea urchins occurred only on the cobbles and crustose corallines in contrast to the presence of 2‐year‐old individuals from all areas and the restricted distribution of individuals aged 3 years and over to Eisenia and crustose corallines. Calculated mean body sizes in the Eisenia area became larger after the age of 2 years compared with those in the area of crustose corallines. Spawning was ascertained histologically in both the Eisenia and crustose coralline areas, although gonad indices were higher in the former area than in the latter throughout the year. Gut contents were dominated by E. bicyclis in the Eisenia area, and by crustose coralline red algae and small algae in the crustose coralline area. Thus, the sea urchin may settle most abundantly on crustose corallines and lives there for 1–2 years. Thereafter, they expand their habitat toward the Eisenia area, where there is richer sources of food for attaining a higher growth rate and to generate heavier gonads.