Predator–prey systems of drifting seaweed communities offthe Tohoku coast, northern Japan, as determined by feeding habitanalysis of phytal animals

ABSTRACT:   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).