Changes of Diatom Community on Plastic Plates Used for Rearing of Abalone Nordotis discus

Abstract

Sessile diatom communities on plastic plates used for rearing of juvenile abalone, Nordotis discus, were observed in detail at Banda Marine Laboratory of Tokyo University of Fisheries in Chiba Prefecture. The plastic plates were put in an outdoor tank without abalone. Within seven to ten days, the plates were fouled with the thick filaments of diatoms such as Navicula britannica, Nitzschia closterium, N. longissima and Bacillaria paxillifera, which formed stratified overstock assemblages. After abalone introduction onto the plates, these diatoms disappeared; and Cocconeis dirupta, C. scutellum var. scutellum, and C. scutellum var. ornata proliferated remarkably and assemblages became a uniform layer of prostrate cells. It was suggested that these prostrate diatoms were suitable initial food for creeping juveniles of abalone. In the absence of grazing pressure by abalone, the algal community on the plate did not result in uniform layer assemblage.