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

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.