Spatial variation in microalgal colonization on hard surfaces in a lentic freshwater environment

Qualitative and quantitative aspects of mesoscale spatial variation in microalgal colonization on Perspex panels were studied in a freshwater reservoir with a water spread of 1.7 hectares which experiences hardly any disturbance in terms of wave movement or current. Perspex panels of different sizes (3 x 3; 7 x 3 and 10 x 7 cm) were suspended at a depth of 0.5 m and the early stages (first 15d) of colonization were followed. The algal biofilms that formed at the periphery of the panels were significantly different in thickness (P < 0.0001) and total algal density (P < 0.0001) from those at the centre. However, species richness was higher at the centre of the panels than at periphery (P < 0.0054). The filamentous cyanobacterium Calothrix sp. and the stalked diatom Gomphoneis olivaceum were dominant at the periphery, while the unicellular green alga Chlorella sp., colonial forms such as Pediastrum boryanum and Coleochaete scutata were more dense at the panel centres. Algal density was slightly higher on smaller panels than on larger ones. An 'edge effect' was observed on all the panels (different sizes) tested. The pattern of microalgal succession in the centre and at the periphery was found to be different over a period of time on all panel sizes. The results indicate the significance of 1) mesoscale variations in relative water movement (however weak) in influencing microalgal colonization on hard surfaces and 2) the significance of substratum configuration on the colonization pattern of a periphyton community even in a lentic ecosystem.