Grazing selectivity of red abalone Haliotis rufescens postlarvae on benthic diatom films under culture conditions

The gut contents of Haliotis rufescens postlarvae that had grazed on a diat om film grown in PVC buckets were analyzed to determine selectivity in feed ing. Species composition and abundances were compared to that of the surrou nding film. Diatom samples were oxydized and mounted permanently, or observ ed directly by the squash technique under phase contrast microscopy. The su rrounding flora yielded 111 taxa, while 64 species appeared in the gut cont ents, A high proportion of Pinnularia biceps v. minor and Navicula incerta (and others) in the gut contents, which were rare or absent from the sample s of the surrounding flora, indicated grazing selectivity by the postlarvae . An analysis of similarity confirmed that samples from the gut contents co uld be grouped together and that they were clearly different from the surro unding flora.