A field study was conducted to evaluate the protozoan colonization patterns on artificial substrates in relation to organic pollution within a tropical harbour. The composition of protozoans and their succession rates on artificial substrates(polyurethane foam units) were compared between two field stations(A and B), and their presence were considered with regards to the prevailing water quality conditions at the study sites. Altogether 44 genera of flagellates and ciliates were documented. The common genera of flagellates encountered included Monas, Polytoma, and Chromalina. Among the ciliates, the predominant genera were Tetrahymena, Vorticella, Lagynophyra, and Heloiphyra. These groups exhibited characteristic successional patterns in relation to ambient water quality. At Station A, located close to the sewage outfall, the water quality parameters included poor Secchi disc transparency(0.48m), dissolved oxygen of 1.93 mg/ml, salinity of 18 psu, and temperature 31.3 ℃. Here, the nanoflagellates( spumella ) colonized first, followed by microcilliate( Tetrahymena ) and sessile form( Vorticella ). Station B, located on the seaward side, was characterized by relatively less stressed environmental conditions with transparency 1.85m and dissolved oxygen value of 6 04 mg/ml. Salinity of 27.27 psu, and mean temperature of 30 ℃ were recorded at “B". At this station, the nanoflagellate Polytoma was first documented to colonize on the substrates, followed by microcilliate( Lagynophrya ) and suctorid( Heliophyra ). These findings support the use of protozoans as indicator species for evaluating the hazards posed by organic pollution to natural estuarine communities.
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