CHEMICAL CONSEQUENCES OF RELOCATION OF THE SOFT CORAL LOBOPHYTUM COMPACTUM AND ITS PLACEMENT IN CONTACT WITH THE RED ALGA PLOCAMIUM-HAMATUM

Seven colonies of Lobophytum compactum Tixier-Durivault, 1956, which p roduce isolobophytolide as the major secondary metabolite, were select ed from a fringing reef in the Pelorus Channel, Palm Island Group (18 degrees 34'S; 146 degrees 29'E), North Queensland, Australia. In Septe mber 1991, they were sectioned to afford two portions which were reloc ated to a grid, and a significant part of the parent colony which was left in place. The aim of the experiment was to determine the effect o f relocation and contact with a toxic alga on the secondary metabolite content of a soft coral. A significant increase in the concentration of isolobophytolide was observed for all relocated colonies (n = 14, p = 0.001) compared to the non-relocated control colonies. This decreas ed after 2 mo, and was not significantly different from that of the no n-relocated control colonies (n = 14, p = 0.881). After 1 mo, Plocamiu m hamatum J. Agardh plants were placed in direct contact with 50% of t he relocated colonies. All soft-coral colonies in contact with the alg a (n = 7), showed tissue necrosis on the parts in direct contact with the alga after a further 2 wk. Tissues of the relocated control coloni es (n = 7), and those portions of treated colonies which were not in d irect contact with the alga, were not affected. The parts of the colon ies in contact with the alga showed a significant decrease in lipid co ntent over time (n = 7, p < 0.001) and also a decrease in the concentr ation of the diterpene isolobophytolide (n = 7, p < 0.001). The effect s of P. hamatum on the soft coral were essentially restricted to contr act necrosis; chemical variations in the affected tissue were the outc omes of this necrosis. These results indicate that stress due to reloc ation is a more important factor in the variation of isolobophytolide levels in the soft coral L. compactum than is contact with the alga P. hamatum.