STUDY ON THE EVALUATION OF ECOSYSTEM FUNCTION OF OKINAWA TIDAL FLATS

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Ecosystem function of tidal flat was theoretically analyzed and they were evaluated quantitatively. It has several functions such as 1) Resting and feeding sites for bids, 2) Environmental purification ground of organic materials carried by river system, 3) Beautiful landscape, 4) Site for recreation, 5) Fishery ground, and 6) Site for research and education.Quantitative analysis of the function of environmental purification was conducted by evaluating the feeding activity of the fiddler crab Uca vocans vocans. Considering its density, diurnal activity rhythm and its ambient environment, 20-80 kg of organic nitrogen were estimated to be consumed in the area of 1 ha. If deposit feeders do not occur on the tidal flat, a reduced environment might appear according to the accumulation of a huge amount of organic matter. Feeding activity of other dominant species should be studied in detail and total activity of benthic animals should also be estimated.On the other hand, filtration of sea water by sandy beach was analyzed. In a sandy beach of 1 km long, about 70 metric tons of sea water were estimated to be filtered. COD which is an indicator of the amount of organic matter in an environment apparently decreased after the filtration by the sandy beach.Dynamics of organic matter on tidal flat, sandy beach and coral reef should be analyzed with reference to the its inflow from river system, and ecosystem function of tidal flat should be discussed more quantitatively.