Early stages of biofilm succession in a lentic freshwater environment

Initial events of biofilms development and succession were studied in a freshwater environment at Kalpakkam, East Coast of India. Biofilms were developed by suspending Perspex (Plexiglass) panels for 15 days at bimonthly intervals from January 1996 to January 1997. Changes in biofilm thickness, biomass, algal density, chlorophyll a concentration and species composition were monitored. The biofilm thickness, biomass, algal density and chlorophyll a concentration increased with biofilms age and colonization was greater during summer (March, May and July) than other months. The initial colonization was mainly composed of Chlorella vulgaris, Chlorococcum humicolo (green algae), Achnanthes minutissima, Cocconeis scutellum, C. placentula (diatoms) and Chroococcus minutus (cyanobacteria) followed by colonial green algae such as Pediastrum tetras, P. boryanumand Coleochaete scutata, cyanobacteria (Gloeocapsa nigrescens), low profile diatoms (Amphora coffeaeformis, Nitzschia amphibia, and Gomphonema parvulum) and long stalked diatoms (Gomphoneis olivaceumand Gomphonema lanceolatum). After the 10th day, the community consisted of filamentous green algae (Klebshormidium subtile, Oedogonium sp., Stigeoclonium tenue and Ulothrix zonata) and cyanobacteria (Calothrix elenkinii, Oscillatoria tenuis and Phormidium tenue). Based on the percentage composition of different groups in the biofilm, three phases of succession could be identified: the first phase was dominated by green algae, the second by diatoms and the third phase by cyanobacteria. Seasonal variation in species composition was observed but the sequence of colonization was similar throughout the study period.