We studied a tropical mangrove ecosystem, situated at Pichavaram, southeast India. We found 13 species of mangrove trees, with Avicennia marina and Rhizophora species predominant, besides 73 spp. of other plants, 52 spp. of bacteria, 23 spp. of fungi, 82 spp. of phytoplankton, 22 spp. of seaweeds, 3 spp. of seagrass, 95 spp. of zooplankton, 40 spp. of meiobenthos, 52 spp. of macrobenthos, 177 spp. of fish and 200 spp. of birds. The bacteria performed activities like photosynthesis, methanogenesis, magnetic behaviour, human pathogens and production of antibiotics and enzymes (arysulphatase, L-glutaminase, chitinase, L-asparaginase, cellulase, protease, phosphatase). The microzooplankton included tintinnids, rotifers, nauplius stages of copepods and veliger larvae of molluscs, with a predominance of tintinnids. Tintinopsis spp. alone accounted for 90% of abundance. The macrozooplankton consisted of 95% of copepods and coelenterates. The meiofauna was rich with nematodes (50-70% of the component), followed by foramifera. The macrofauna included polychaetes, bivalves, gastropods, tanaids, isopods, amphipods, cirripedes, crabs, hermit crabs and shrimps. The mangrove harboured a large number of juvenile fishes, especially during summer and post-monsoon. The water was fertile and productive in having several fold-higher levels of nutrients, microbes, plankton and other biological resources, than the adjoining estuarine, backwater and neritic environments. The gross primary production was 8 g cm(-3) d(-1); about 21% of which was contributed by phytoplankton of 5-10 mu m size. Unfortunately, 90% of the mangrove cover in the study area was degraded. Possible factors that cause degradation of the ecosystem are detailed and remedial measures suggested. Techniques for regeneration of the degraded areas are proposed.
