Study was made on the occurrence of bryozoa and their preference in substrata for colonisation in various aquatic biotopes at Parangipettai. During summer and premonsoon seasons their population increased whereas during monsoon it declined. Five species were recorded in the Vellar estuary and 6 species in the mangroves of Pichavaram. The stilt roots of Rhizophora apiculata were preferred by 5 species for their settlement. In the backwater biotope, colonies of Membranipora tuherculata were observed as encrustations upon the oyster beds.