Isopod and insect root borers may benefit Florida mangroves

Far from threatening the persistence and geographic extent of red mangrove (Rhizophora mangle) in Florida, wood-boring marine isopods may aid the plant to survive wave action by initiating branching of aerial prop roots. Evidence for a recent, sudden increase in density or range of one such isopod, Sphaeroma terebrans, is anecdotal and weak. Insect damage to mangrove aerial roots even before they descend to the water is at least as great as that wrought by isopods and also causes root branching. Aerial and submarine damage combine to stimulate root initiation so that, for every root produced aerially by the tree, at least 1.4 roots reach the substrate. Similar responses to herbivory, which have been reported for other plants, suggest that herbivores may both benefit and harm plants, and that their impact may be more difficult to assess in specific instances than has been realized.