Factors driving epilithic algal colonization in show caves and new insights into combating biofilm development with UV-C treatments Fabien Borderie a , Nicolas Tête a , Didier Cailhol c , Laurence Alaoui-Sehmer a , Faisl Bousta b , Dominique Rieffel a , Lotfi Aleya a, ⁎, Badr Alaoui-Sossé a a Laboratoire Chrono-Environnement (LCE), UMR CNRS 6249, Université de Franche-Comté, Place Leclerc, F-25030 Besançon, France b Laboratoire de Recherche des Monuments Historiques (LRMH), USR 3224, 29 rue de Paris, F-77420 Champs-sur-Marne, France c Laboratoire Environnement, Dynamique et Territoires de Montagne (EDYTEM), UMR CNRS 5204, Université de Savoie, F-73376 Le Bourget du Lac, France HIGHLIGHTS • Growth-influencing factors of epilithic algae in a show cave were studied. • Not one but a combination of factors explained the presence of algae. • Colorimetric measurements are a good diagnosis of colonization state. • Effects of UV-C treatments were investigated on several green biofilms. • Treated biofilms are bleached but re-colonization occurs after 16 months. abstract article info Article history: Received 7 January 2014 Received in revised form 7 March 2014 Accepted 11 March 2014 Available online xxxx Editor: C.E.W. Steinberg Keywords: Epilithic algae Biofilms Cave Growth-influencing factors Colorimetric measurements UV-C treatment The proliferation of epilithic algae that form biofilms in subterranean environments, such as show caves, is a major problem for conservators. In an effort to reduce the use of chemical cleansers when addressing this problem, we proposed investigating the effects of UV-C on combating algal biofilm expansion in a cave located in northeastern France (Moidons Cave). First, the biofilms and cavity were studied in terms of their algal growth-influencing factors to understand the dynamics of colonization in these very harsh environments. Next, colorimetric measurements were used both to diagnose the initial colonization state and monitor the UV-C-treated biofilms for several months after irradiation. The results indicated that passive dispersal vectors of the viable spores and cells were the primary factors involved in the cave's algae repartition. The illumination time during visits appeared to be responsible for greater colonization in some parts of the cave. We also showed that colorimetric measurements could be used for the detection of both thin and thick biofilms, regardless of the type of colonized surface. Finally, our results showed that UV-C treatment led to bleaching of the treated biofilm due to chlorophyll degradation even one year after UV-C treatment. However, a re-colonization phenomenon was colorimetrically and visually detected 16 months later, suggesting that the colonization dynamics had not been fully halted. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Caves are probably the most particular ecosystem, as they harbor life despite their lack of sunlight and reminding us of how life on earth may have first begun. While light-driven photosynthetic production by plants is the key source of energy in outdoor ecosystems, chemical- driven microbial production can support food webs in caves (Simon, 2012). However, the discovery of a given cave and its opening to the public give irremediable rise to a combination of structural changes that greatly affect its relatively stable microclimate (Groth et al., 1999). The installation of a lighting system to make cave formations vis- ible to visiting tourists may, over time, lead to the appearance of green- ish biofilms due to the growth of prototrophs such as algae and cyanobacteria, which are considered a major source of biodeterioration on rock surfaces (Albertano, 2012; Cutler et al., 2013). These colonists, or “r-selected species,” possess invasive, fast-growing and prolific prop- agule production and are later joined by more varied, larger and more slowly growing species, and eventually by species that, through the ex- clusion of their competitors, achieve complete dominance over an eco- logical climax (Aleya, 1991). The Moidons Cave (Jura, France), discovered in 1966 and open to tourists for 6 months a year since 1989, may constitute a plausible ex- ample of this phenomenon. Each year, approximately 25,000 people Science of the Total Environment 484 (2014) 43–52 ⁎ Corresponding author. Tel.: +33 3 81 66 57 64; fax: +33 3 81 66 57 97. E-mail address: lotfi.aleya@univ-fcomte.fr (L. Aleya). http://dx.doi.org/10.1016/j.scitotenv.2014.03.043 0048-9697/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv