Contribution by microbes to the foodweb of a mangrove biotope: the approach of carbon and nitrogen stable isotopes

The contribution of mangroves as a source of nutrients to the foodweb of fish is under debate worldwide. An analysis of stable isotopes of carbon and nitrogen in various consumers and producers of a mangrove biotope in southern India revealed that the microbes associated with mangrove sediment contribute significantly to the foodwebs. The prominent species of microbes in mangrove sediments included Aeromonas hydrophila, A. punctata, Azotobacter beijerinckii, A. vinelandii, A. chroococcum, Bacillus cereus, Corynebacterium xerosis, Escherichia coli, Lactobacillus sp. and Pseudomonas aeruginosa. However, the contribution of phytoplankton to the foodweb progressively increases with distance offshore. Hence, in a detritus-based mangrove region, the mangroves perpetuate microbes in the sediment and they act as important primary producers, whereas in non-mangrove regions, the microbes enhance the nutrient concentrations required for phytoplankton and so play an intermediate role.