Mangroves and microbes, coordinated ecosystem engineers in Coastal Ecuador

Mangrove forests occupy a large portion of the world’s tropical and subtropical coastlines, but land use changes and eutrophication have caused degradation and loss of mangrove habitat. Within mangrove-dominated estuaries, water column microbes are essential to many important ecosystem processes such as carbon and nutrient cycling, and may contribute to the health of the overall mangrove ecosystem. However, the bacterial response to land use changes and aquaculture effluent is poorly understood. In this study we used 16S and 18S rRNA gene analysis, nutrient concentrations, C and N isotopes, and acoustic Doppler current profiling (ADCP) data to evaluate the impact of mangrove land use change on near-shore biogeochemical and hydrodynamic processes in northern coastal Ecuador. Changes in microbial community structure and nutrient concentrations were associated with gradients in salinity and land use. Elevated levels of NH4+, PO43-, chlorophyll, and low diversity characterized the high aquaculture effluent sites. The microbial community composition at these sites had a distinctive signature associated to Fusobacterium, Desulfovibrio and Chromatiaceae bacterium and reduction of nitrogen fixers organisms (i.e. Oscillatorias species). The complex hydrodynamic processes in mangrove forests revealed spatial variability among microbial communities with fluctuations during flood and ebb tide cycles with implications in biogeochemical processes. These results highlight the sensitivity of the mangrove-estuarine microbial community, and their ecosystem functions, to land use changes and further implications in altering mangrove’s ecosystem health and resilience.