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

Abstract

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.KEY WORDS: Beneficial herbivory · Florida · Isopod · Mangrove · Plant-animal interaction · Prop root · Repair · Rhizophora mangle · Sphaeroma terebrans · Tolerance · Wood borer Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 231: [85][86][87][88][89][90] 2002 sation (i.e. repair and regrowth of tissue) for loss due to herbivory, leading to an overcompensation in production. In these latter cases, the plant-animal interaction is considered 'beneficial herbivory' or 'overcompensation' (sensu Paige & Whitham 1987, Paige 1992, 1999, Lennartsson et al. 1998, Agrawal 2000. The 2 herbivore response strategies (i.e. avoidance and tolerance) may not be mutually exclusive, however, and some species may demonstrate levels of both (Fineblum & Rausher 1995, Mauricio et al. 1997.The red mangrove Rhizophora mangle L. produces aerial prop roots from the bole, trunk, and other aboveground roots which grow down through the water column and eventually attach to the substratum (Gill & Tomlinson 1977). The aerial portion of these prop roots has secondary vascular development and thick surface cells that are not found in the subterranean part of the root once it attaches (Gill & Tomlinson 1975). Worldwide, the wood boring isopod Sphaeroma terebrans Bate exploits the intertidal habitat created by prop roots in the fringing red mangrove (Rehm & Humm 1973, Estevez 1978. The relationship between S. ...

Rhizophora stylosa prop roots even when damaged prevent wood-boring teredinids from toppling the trees

“…Trees affected by isopods may suffer lower performance as photosynthesis, gaseous exchange and nutrient uptake would be reduced compared to uneaten trees. The total effect of minor damage can therefore negatively affect trees by diverting energy to repairing the damage (Brooks & Bell, 2002), compromising root and tree fitness. However, it is thought that sphaeromids are unable to burrow into older developed roots that reach the substratum due to the development of woody tissue in the older roots (Perry, 1988).…”

“…Some trees are protected from herbivorous attack by their chemical and structural anti-herbivore defence mechanisms (Turner, 1976;Brooks & Bell, 2002). Plants are able to survive in environments where herbivores are common due to their ability to resist or recover from repeated herbivory (Brooks & Bell, 2002;Hanley et al, 2007).…”

“…Plants are able to survive in environments where herbivores are common due to their ability to resist or recover from repeated herbivory (Brooks & Bell, 2002;Hanley et al, 2007). To combat attack, some plants release tannins (Bloch, 1952;Alongi, 1987).…”

“…Compartmentalising sets boundaries that resist the spread of the invading microorganisms (Shigo, 1985). Mangrove plants may likely use the tolerance strategy against damage or stress (Brooks & Bell, 2002), as many other angiosperms have evolved this response to combat herbivore attack . Mangroves may also be particularly resilient to stress because of the nature of the environment.…”

“…Plants also express resistance to herbivory via strategies labelled as tolerance mechanisms (Paige, 1999;Brooks & Bell, 2002), defined as tissue repair and regrowth after exposure from stress. Tissue regeneration reduces the risk from potential infection (Wier et al, 1996).…”