Mangrove response to attack by a root boring isopod: root repair versus architectural modification

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The nature of the plant-animal interaction between wood-boring isopods and the red mangrove Rhizophora mangle L. has been controversial, with discussion ranging from the damage caused by the isopod being detrimental to beneficial for the mangroves they attack. Initiation of lateral roots by the mangrove in response to isopod burrowing has been one of the most commonly cited examples as support for the concept of beneficial herbivory. In this study, the possibility of root repair as a response of Rhizophora to burrowing by Sphaeroma terebrans Bate was evaluated. Previously burrowed prop roots were tagged in the field and the fate of all burrows followed over 14 wk at a site in Upper Tampa Bay, Florida. Results demonstrated that the most common response of the mangrove was to repair abandoned isopod burrows, with 99 % of all tagged roots and 66 % of all monitored burrows showing signs of repair. Lateral root production occurred at a lower frequency (32 % of roots). Similarly, transect surveys performed in Upper Tampa Bay and 2 additional locations (Anna Maria Island and Weedon Island) indicated a high incidence (57 to 82 %) of attacked aerial roots showing signs of burrow repair. Again, lateral root production was less commonly noted on transects (13 to 25 % of the roots surveyed). Initiation of lateral roots and burrow repair were not mutually exclusive responses and all instances of lateral root production were in conjunction with repair. Our results demonstrate that the most common response to damage is the replacement of root tissue rather than the stimulation of new tissue production.