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

Abstract

This study examines the ability of live Rhizophora stylosa prop roots to heal damaged tissues and defend against herbivorous attack from teredinids in three mangrove forests. Sites were chosen because damaged roots and teredinid activity were frequent. Responses of 81 R. stylosa roots to three levels of experimental damage were investigated: superficial, moderate and severe. Tannin intensity post damage was analysed using ImageJ. Losses of tissue and numbers of teredinid tunnels within damaged roots among sites were not significant in magnitude. Tissue regrowth varied significantly among roots; moderately damaged roots had an over compensatory regrowth of tissue. Yet, few roots with severe damage demonstrated the same level of excessive tissue regrowth, and many roots lost tissue to necrosis and teredinid attack. Superficially damaged roots did not succumb to teredinid attack. Rhizophora stylosa roots are able to defend against teredinid larval settlement by production of tannins in damaged cortex tissue and by an over compensatory regrowth. This study highlights the resilience and ability of mangroves to heal damaged roots and defend against woodborers. But, when losses of tissues expose the vascular cylinder, teredinid larvae will settle and tunnel into the root. The roots are then open to infection, and cell necrosis.