LARVAL DEVELOPMENT OF BALANUS AMPHITRITE VAR. DENTICULATA BROCH REARED IN THE LABORATORY

Abstract

While there have been numerous studies on Cirripedia larvae based on reconstructed life-histories, to date there have been only three reports on nauplii reared from the egg through all larval stages to the sessile form, that of Herz (1933) for Balanus crenatus, Hudinaga and Kasahara (1941) for Balanus amphitrite hawaiiensis, and Costlow and Bookhout (1957) for Balanus eburneus. This method has the advantage over reconstructed life-histories in that one can be sure of the identity of the adult, the source of eggs and future larvae. Once the life-histories of all species of barnacles in a given area have been described, ecological studies may be made with a greater degree of assurance. Ecological investigations based on sampling, such as that of Bousfield (1955), may provide the number of stages, the approximate duration and mortality of the individual stages, and the distribution and fluctuations in large populations. Laboratory studies on individually reared larvae, however, can give more detailed information on all phases of the life-history other than distribution and population fluctuations. Both types of research are required before a complete picture can be obtained. Laboratory studies are necessarily prerequisite to physiological and genetic investigations. Balanus amphitrite denticulata Broch is one of the most widely distributed acorn barnacles. It has been reported from the tidal waters of Britain which are artificially heated by industrial effluents (Crisp and Molesworth, 1951), the estuaries of South Africa (Sandison, 1954), and the East and West coasts of North America (Dr. Dora Henry, personal communications). In spite of its world-wide distribution only the first two larval stages have been described (Sandison, 1954). Bishop (1950) believes that Balanus amphitrite denticulata merits a more thorough study and questions its position as a variety of B. amphitrite. Thus it should be of interest to compare the larval development of this variety with the descriptions of larvae of Balinus amphitrite albicostatus (Ishida and Yasugi, 1937) and Balanus amphitrite hawaiiensis (Hudinaga and Kasahara, 1941). Balanus amphitrite denticulata is the most abundant fouling organism in the inter-tidal region at Beaufort, North Carolina and breeds during the same summer months as Balanus eburneus. During the past two years we have followed the larval development of B. amphitrite denticulata in the laboratory to determine the number of stages, the frequency of molting, and the duration of the intermolt periods. Our secondary objectives were to compare the appendage setation and body form with the corresponding naupliar stages of the other two varieties of Balanus amphitrite which have been described and with the larvae of barnacles belonging to different species and genera.