applied on periphyton weight. The effects of added filtered seawater (7/16 of 200 ml or 40 ml according to the type of sampling) on DW,ASH and AFDW of periphyton were determined considering the salinity of the cleaning water and the corresponding calibration curves (DW(g L−1)=1.17 Salinity (R2=0.99), ASH (g L−1)=0.94 Salinity (R2=0.99), and AFDW (g L−1)=0.23 Salinity (R2=0.96).