The influence of mangrove-derived tannins on intertidal meiobenthos in tropical estuaries

Mangrove-derived tannins negatively effected laboratory-reared nematode populations and natural communities of meiobenthos in tropical mangrove forests along the northeastern coast of Australia. In the low and mid intertidal zones of five mangrove estuaries, nearly all of the dominant meiofaunal taxa correlated negatively with concentrations of sediment tannins. Only nematodes correlated with low tannin concentrations in the high intertidal zones. The negative exponential equation y=be ^-mx represented the best-fit for most of the meiofauna-tannin relationships. The mangrove-dwelling nematode, Terschellingia longicaudata did not grow (r=0.001) in the laboratory on fresh, tannin-rich leaves of the red mangrove, Rhizophora stylosa. Population growth of the nematode was significantly greater on fresh, tannin-poor leaves of the grey mangrove, Avicennia marina (r=0.081) with best growth (r=0.112) attained on a diet of tannin-free, mixed cereal. These preliminary field and laboratory results suggest that hydrolyzable tannins leached from mangrove roots and leaf litter are an important factor regulating intertidal meiobenthic communities in tropical mangrove forests along the northeastern Australian coast.