Ecological functioning of free-living marine nematodes in coastal wetlands: an overview

Nematodes are small multicellular, thread-like organisms, inhabiting almost all conceivable environments; among these, some 25 % are free-living marine forms with a population density of (1-12) x 10(6) inds m(-2) in seabed sediment, reaching maximum values in muddy estuaries and salt marshes. A large quantity of carbon from the salt marsh plants enters the ecosystem via the detritus pathway, in which nematodes play an important role through their feeding and bioturbation activities. Vegetation influences the sedimentary environment and modifies the distribution pattern of nematode communities in coastal wetlands. Nematodes are coupled closely with bacteria/detritus in microbial food webs, stimulating bacterial growth and subsequent nutrient remineralization; they provide food sources for higher trophic levels and serve as a linkage between micro- and macro-fauna. Furthermore, nematodes have a potential to provide proxies that can be used in diagnosing environmental quality. In China, only a limited number of nematode data sets are available for the coastal wetlands across several different climatic zones. It is necessary to carry out additional investigations into the biology and ecology of nematodes in order to delineate their ecological functioning in coastal wetlands. On such a basis, the contribution made by nematodes to material cycling and the ecological functioning in coastal wetlands can be quantified. The assessment of their biological diversity should be a focus, which is fundamental in the study of wetland ecosystem dynamic mechanisms. In addition to laboratory and mesocosm experiments, mathematical models should be established to predict the responses of ecosystem to the environmental disturbance. Finally, it is necessary to improve the techniques for nematode analysis, to enhance the efficiency of data acquisition.