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 produce isolobophytolide as the major secondary metabolite, were selected from a fringing reef in the Pelorus Channel, Palm Island Group (18°34S; 146°29E), North Queensland, Australia. In September 1991, they were sectioned to afford two portions which were relocated 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 of 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 decreased after 2 mo, and was not significantly different from that of the non-relocated control colonies (n=14, p=0.881). After 1 mo, Plocamium hamatum J. Agardh plants were placed in direct contact with 50% of the relocated colonies. All soft-coral colonies in contact with the alga (n=7), showed tissue necrosis on the parts in direct contact with the alga after a further 2 wk. Tissues of the relocated control colonies (n=7), and those portions of treated colonies which were not in direct contact with the alga, were not affected. The parts of the colonies in contact with the alga showed a significant decrease in lipid content over time (n=7, p=0.001) and also a decrease in the concentration of the diterpene isolobophytolide (n=7, p=0.001). The effects of P. hamatum on the soft coral were essentially restricted to contract necrosis; chemical variations in the affected tissue were the outcomes of this necrosis. These results indicate that stress due to relocation 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.