Damage and alteration of mangroves inhabited by a marine wood-borer

Abstract

Animals can exert a strong influence on the structure and function of foundation species such as mangroves. Because mangroves live at the interface of land and sea, both terrestrial and marine species affect them, including numerous herbivores and boring species. These organisms can affect the fecundity, performance, and morphology of mangroves. In a mangrove stand in southwestern Taiwan, we discovered that mangroves were extensively damaged by woodboring isopods Sphaeroma terebrans. We examined the relationships between burrowing damage from S. terebrans and metrics of mangrove fecundity, performance, and morphology. Individuals of Rhizophora stylosa that were more burrowed by isopods had significantly fewer propagules, fewer ground roots stabilizing the tree, smaller leaves, and more non-foliated twigs. Similarly, Avicennia marina with more burrows had fewer pneumatophores and lenticels (used for gaseous exchange), and pneumatophores with more necrotic tissue. The most heavily damaged trees were hollowed-out with burrows (A. marina) or fell over when their supportive root system failed (R. stylosa). These correlations suggest that marine wood-borers can negatively influence mangroves and alter tree morphology, although other stressors may also be involved. While studies have examined the effects of isopods on root-level production, we provide the first quantitative evidence that localized burrowing damage is correlated with tree-level effects. These results are consistent with other literature demonstrating the importance of sub-lethal damage by borers in shaping foundation species. Such damage may have cascading effects on the diverse assemblages of marine and terrestrial biota that use mangroves as habitat.KEY WORDS: Habitat alteration · Mangrove · Plant−animal interactions · Sphaeroma terebrans · Sub-lethal stress Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 516: [177][178][179][180][181][182][183][184][185] 2014 mangrove roots, which can have mech anical and physiological consequences. The aerial roots of red mangroves buttress and anchor the tree; the destruction of aerial roots by isopods has been suggested to increase the susceptibility of mangroves to damage from storms (Rehm & Humm 1973, Santhakumari 1991. While burrowing by sphaeromatid isopods can initiate root branching (Simberloff et al. 1978, Perry & Brusca 1989, these sub-lethal burrowing effects cause a net reduction in root growth and productivity (Perry & Brusca 1989, Brooks & Bell 2002) and divert resources from production to repair (Brooks & Bell 2002). Roots are also important for gaseous exchange and nutrient absorption, and they are photosynthetic (Gill & Tomlinson 1977, Tomlinson 1986, Kitaya et al. 2002. Because borer damage diverts resources from the generation of propagules, leaves, and other structures to repair, we hypothesize that high levels of isopod boring may affect unbored parts of the tree. However, most relevant studies are anecdotal or focus on isopod interact...

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

“…However, studies have shown that the cumulative effect of localised isopod borer damage can scale up to negatively affect the whole tree (Perry, 1988;Brooks & Bell, 2002). Mangroves with many isopod burrows have significantly fewer propagules, ground roots and pneumatophores when compared with non-burrowed conspecifics (Davidson et al, 2014). However, teredinids are the only borers able to penetrate the thicker woody tissue.…”

Boring crustaceans shape the land–sea interface in brackish Caribbean mangroves

“…Sphaeroma terebrans is broadly distributed throughout brackish waters along the Atlantic coast of the Americas from Brazil to Virginia (USA), West and East Africa, India, and in the western Pacific from Australia to Taiwan (Harrison and Holdich , Kensley and Schotte , Davidson et al. ). Sphaeroma terebrans is thought to be introduced to the Caribbean and Florida from the Indo‐Pacific (Carlton and Ruckelshaus ), but other authors consider the species cosmopolitan (Baratti et al.…”

“…Correlative studies from its native range suggest S. terebrans can be damaging to mangroves (Santhakumari , Davidson et al. ), but most studies document the species boring into dead wood or marine structures (Pillai , Harrison and Holdich ). However, studies from Florida mostly document S. terebrans inhabiting the soft aerial root tips of red mangroves ( Rhizophora spp.)…”

“…Some studies suggest that the effects of boring by sphaeromatid isopods may scale up to cause the toppling of trees (Rehm and Humm ), alter tree‐level morphology (Davidson et al. ), or modify tree and root architecture (Simberloff et al. , Brooks and Bell ).…”

“…, Santhakumari , Davidson et al. ). Since isopod boring truncates roots and may prevent root anchorage in sediment (Rehm and Humm ), S. terebrans could alter mangrove root habitat for marine species and potentially limit the seaward extent of brackish Caribbean and Florida mangroves.…”