Changes of Algal Community on the Plastic Plates used for Rearing the Abalone Haliotis discus hannai

Abstract

In the seed production system of the abalone Haliotis discus hannai, sessile algal communities on the rearing plates are classified into two categories; the first and the second phase algae. The changes from the firs to the second phase algae were observed in detail. On the rearing plates, Licmophora abbreviata, Achnanthes javanica f. subconstricta, A. kuwaitensis, Navicula ramosissima, Nitzschia closterium and N. acicularis were observed abundantly as the first phase algae, and they built up stratified overstory assemblages. After the introduction of juveniles of the abalone onto the plates, these algae disappeared, and Cocconeis costata, C. scutellum, C. sublitoralis and Myrionema sp. proliferated remazkably and assemblages became a uniform layer of prostrate cells. These second phase algae were seen in small numbers in the early stages before introducing the abalone juveniles. Without grazing pressure of the juveniles, the algal community on the plates did not change to a uniformly layered assemblage. The first and the second phase algae differed in community structure and dominant species. In addition to these differences, the second phase algae were characterized by the remarkable proliferation under grazing pressure.