Algal colonization and its ecophysiology on the fine sculptures of terracotta monuments of Bishnupur, West Bengal, India

Abstract

The blackish brown crust on the fine carvings of seven terracotta monuments of Bishnupur were studied with regards to the presence of algal species. Forty five taxa of micro algae belonging to 36 species of cyanobacteria, 5 species of chlorophyta and 4 species of bacillariophyta were found in crusts of these monuments. Among the algal groups, cyanobacteria were the dominant population growing in all the monuments with maximum diversity of 30 species in Rasmancha. Lyngbya corticicola, Scytonema schmidtii and Nostoc microscopicum were the major taxa in all crust samples. The absorption ratio of chlorophyll: carotenoid: MAAs (mycosporine-like amino acid substances) and scytonemin showed scytonemin and MAAs were more abundant than the chlorophyll pigment in all the crust. The MAAs and scytonemin of the crusts were identified as Mycosporine glycine having absorption maxima at 310 nm with retention time (RT) 4.1 min and scytonine having absorption maxima 386 nm with RT 3.2 min respectively. Among the major crust cyanobacteria cellular carbohydrate of N. microscopicum was maximum and lowest in S. schmidtii. However, the extra polymeric substance released to the medium was more in L. corticicola and so intense that the medium become coloured. The slimes of the major crust cyanobacteria plug the fine carvings of the terracotta structures which led to disfiguration of fine architecture, act as a biofilm that facilitated growth of fungi, lichens and subsequently to mosses and small plants leading to create creaks in the monuments and deteriorate these archeologically important monuments.