Settlement of the fouling community is generally influenced by the physical, chemical and biological properties of the settling surface. The colour of the substratum may also exert an influence on larval settlement. In the present study, the influence of surface colour on the recruitment of fouling communities was investigated by suspending acrylic panels (red, green, blue, white and yellow) in coastal waters. Results showed that the colour of the substratum plays an important role in the recruitment of sessile species. Recruitment was comparatively high on red and blue coloured surfaces. Barnacle and tubeworm recruitment showed significant variation (Tukey test, P < 0.05) between different coloured surfaces. The significant conclusion of this study is that the colour of the artificial substrata should be taken into consideration when interpreting results from short-term biofouling studies.

Small clay cubes, fired at different temperatures and mounted with nylon touch and close fastener (Velcro®) on acrylic glass plates, were used in an experimental design to study colonization of artificial substrata by lichens. The cubes were exposed in alpine streams for either 5–7 y at five different sites in the Swiss Alps: Flüelatal (three sites) and Brigels (Canton of Graubünden), and Eggerberg (Canton of Valais). Only a few cubes were lost, except at two sites, where complete plates were lost – due to the strong water current and, probably, trampling by cattle. After 3 y, freshwater lichens had grown at three sites. At the most elevated site, colonization was observed after 4 y; at one site no lichen growth was recorded. The first colonizers of the new substrata were the locally most common species. Freshwater lichens preferred the surfaces of clay cubes fired at lower temperature, whereas exposed pieces of local rocks were less frequently colonized. Improvements in the experimental design are suggested.

Cette note se propose de confronter l'aptitude de deux indices biotiques à la détermination de la qualité de l'environnement du cours inférieur du Tibre et d'évaluer si et comment la méthode d'échantillonnage peut influencer la valeur finale de ces indices. Une des méthodes met en œuvre un filet troubleau utilisé pendant 3', tandis que les autres sont basées sur l'utilisation de substrats artificiels immergés à chaque station pendant toute la durée de l'étude. Nos résultats semblent démontrer une sensibilité différente pour les deux indices biotiques dans la description des changements de la qualité de l'environnement et une influence significative de la technique d'échantillonnage sur la détermination de la qualité des eaux obtenue avec les indices biotiques.