“…(1) Direct sampling of one of the above communities, the favourite being the epilithon (Sherman & Phinney, 1971;Lange-Bertalot, 1978;Descy, 1979;Rushforth et al, 1986;Leclercq & Manquet, 1987;Sabater & Sabater, 1988;Watanabe et al, 1988. (2) Sampling of artificial substrata placed in the water, the favourite being glass slides (Geitler, 1927;Butcher, 1932;Cattaneo et al, 1975;Deniseger et al, 1986;Patrick, 1949), but plastic (Besch et al, 1972;Antoine & Benson-Evans, 1985;Engelberg, 1987), wood, stones, slices of rock (Antoine & Benson-Evans, 1984;Lay & Ward, 1987) have been used to a lesser degree. For some purposes counting has been abandoned and chlorophyll a has been used to assess biomass; also a few studies have used uptake of 1 4 C (Keithan & Lowe, 1985).…”