J. Exp. Mar. Biol. Ecol. 179 (1994) 195-205 JOURNAL OF EXPERIMENTAL MARINE BIOLOQY AND ECOLOGY Antimicrobial activity and surface bacterial film in marine sponges Mike1 A. Becerro a,*, Nancy I. Lopez b, Xavier Turon ‘, Maria J. Uriz a zyxwvutsrqpo a Centre for Advanced Studies, Cami de Sta Barbara s/n, E-l 7300 Blanes (Girona), Spain: b Institute of Marine Sciences, Barcelona, Spain: ‘Department of Animal Biology, University of Barcelona, Barcelona. Spain (Received 7 June 1993; revision received 3 February 1994; accepted 22 February 1994) zyxwvutsrqponmlkj Abstract The antimicrobial activity of three sponge species was tested against marine benthic bacteria and the presence of epibiotic bacteria on their surfaces was investigated. The aim of the present study was to determine whether there is a correlation between antimicrobial activities and the presence of a bacterial film. Seven benthic bacterial strains were isolated from the vicinity of the sponges and used as assay organisms. Gram-positive and Gram-negative bacteria were equally affected by all the sponge extracts. The encrusting sponge Crumbe crambe featured the strongest antimi- crobial activity in the assays and no bacteria were found on its surface. The other two sponges, Irciniafasciculata and Spongia oficinalis, featured lower antimicrobial activity than C. crambe and the number of bacteria found on their surfaces was of the same order of magnitude as that found on immersed glass slides used as controls. It was concluded that antimicrobial activities detected in laboratory assays were effective as mechanisms to combat microfouling in only some cases, and other possible interpretations are considered. Key words: Antimicrobial activity; Bacterial film; Fouling; Sponge 1. Introduction Bare substratum is usually scarce in rocky littoral communities, and constitutes a limiting resource for benthic organisms (Jackson & Buss, 1975). As a consequence, epibiosis is a widespread phenomenon in these environments. Although fouling seems likely to be disadvantageous to the basibionts, a wide array of responses to this phe- nomenon can be found in nature. On the one hand, basibionts may tolerate different * Corresponding author. 0022-0981/94/%7.00 0 1994 Elsevier Science B.V. All rights reserved SSDI 0022-0981(94)00030-H