Colonisation of Antifouling Paints by Marine Bacteria

Abstract

Antifouling paints, containing either triphenyl tin fluoride or cuprous oxide as the toxin, and their non-toxic, empty-matrix analogs were used in this study. Panels were exposed in tanks of running seawater and their bacterial load estimated from viable counts of surface swabbings. The viable counts indicated broadly similar colonization patterns for the organotin and the 2 empty-matrix paints. Initial colonization was rapid; bacteria were detected within 4 h of immersion; reaching 25-27 cm-2 after 8 h and 215 cm-2 after 4 days. Numbers then oscillated between 215 and 218 cm-2 until the end of the experiment on day 23. Bacteria were not detected on the copper paint until day 3, although by day 10, and for the remainder of the experiment, this paint supported the highest number of bacteria. The initial rate of colonization was essentially the same as for the other three paints (26 cm-2 by day 4; 216 cm-2 by day 8). In addition, samples of exposed panels were taken for direct observation of the developing microfouling communities in the scanning electron microscope. The 2 empty matrix paints acquire a relatively thick fouling layer composed of diverse microorganisms, mostly bacteria and diatoms, bound up with silt. Fouling of the organotin paint was less extensive: bacteria were predominant, forming discrete colonies with the cells often anchored by thin adhesive threads; some patches of silt were also present. The copper paint became colonized by an almost continuous layer of bacteria, embedded in a sheet-like matrix of adhesive polymer. The results are discussed with reference to the toxicity of conventional antifouling compounds to bacteria and the probable effect of bacterial fouling on the leaching of toxins from the paints.