The holdfast fauna eonsystem of Laminaria hyperborea was tested for use as a means of environmental monitoring. Samples of about three litres of holdfast space are desirable sample sizes although one litre is the absolute minimum. Several natural environmental variables, namely fresh water, rock type, depth, exposure and sedimentation were shown to have no significant effects on holdfast fauna composition. In pollution monitoring therefore these can be disregarded as complicating factors. Gradients of heavy metals and water clarity around the U.K. were defined. To these two variables were added those of latitude and longitude, and these four variables have marked effects on holdfast faunas. Changes in holdfast composition at the 35 main sites sampled are interpreted in the light of these variables. Along the North Sea and West coast sewage pollution and heavy metals respectively have a marked effect on the fauna. Along the South coast unidentified variables correlating very closely with longitude are important. Emphasis in interpretation must be placed on numbers of organisms, species richness and diversity in known sample sizes of holdfasts, and on the community trophic structure. Species presence / absence information has no meaning in holdfast work
