Spatial variations in benthic macrofauna and nutrient dynamics in a mangrove forest subject to intense deforestation: Zanzibar, Tanzania

The present study examines the spatial differences in benthic macrofauna an d nutrient dynamics in areas of intense and minimal forestry activity. The study was conducted in the mangrove forest in Kisakasaka, Zanzibar, Tanzani a and samples were taken from two areas with different degrees of deforesta tion; a heavily logged area and an unlogged area. In each area, two 10 x 10 m quadrants were mapped, and pH, temperature and salinity were measured. H istorical information indicated that the areas originally had the same sedi ment type and mangrove species composition. The results of the macrofauna s ampling showed a significant difference between the areas, both quantitativ ely and in species composition. No significant differences were observed in the crab communities between the two different areas, however, examination s of the nutrient content indicated differences in the interstitial water c oncentrations of nitrate, ammonia and phosphate. No differences were found for the reversibly bound ammonium pools. The data obtained suggested a conn ection between the interstitial levels of nitrate and ammonia with the pres ence of roots and the associated bacterial processes in the sediment. Hence , for DIN, there appears to be an impact from logging. By comparison, phosp hate content appeared to be dependent on abiotic factors and, together with ammonia in the solid phase, does not seem to change due to logging. Overal l, this study shows that deforestation leads to rapid changes in the ecosys tem. The study suggests that the rate of logging is unsustainable and that more work is required to better understand the processes involved in logged mangrove ecosystems.