Degrading mangrove leaves of Rhizophora mangle Linne provide a natural cuefor settlement and metamorphosis of the upside down jellyfish Cassiopea xamachana Bigelow

Planula larvae of the tropical jellyfish Cassiopea xamachana Bigelow settle and metamorphose on submerged, degrading leaves of the Red Mangrove Rhizop hora mangle Linne. Other substrata from the habitat were not settled by the larvae in statistically significant numbers. Planulae preferred the shady side of the leaves, as found in situ, for settlement. Polyps already on the leaves had no influence on settlement behavior of new larvae. Antibiotic t reatment of deteriorating mangrove leaves resulted in a significant decreas e of the inductive capacity. Boiling of the leaves significantly reduced th e number of settled and metamorphosed larvae implying denaturation of the n atural inducer. Exposure of leaf fragments in dialysis tubing revealed that the natural cue is water-soluble and smaller than 12 kD. The results of th is study indicate that marine bacteria are involved in the production of at least one peptidic inducer originating from the decomposing mangrove leave s. (C) 1999 Elsevier Science B.V. All rights reserved.