Fucus vesiculosus was transplanted from one locality with an impoverished flora to another with a species-poor but different vegetation. Discs of Fucus thallus incubated in culture showed a significant increase in epiflora in the transplants. The possible applications to routine monitoring of polluted estuaries are discussed.Harmful effects of pollution on the algal biodiversity of estuaries have been reported in numerous floristic studies (e.g. Edwards, 1972). The species-list approach suffers from a number of quite serious flaws: it is highly labour intensive; the absence of sampling rigour makes it difficult to interpret the results; and it is unsuitable as a basis for routine monitoring. In order to overcome these objections, it was decided to see if Fucus vesiculosus L. (Algae: Fucophyceae) a perennial macrophyte with high tolerance to pollution, can function as a trap for spores of smaller algae in the same locality and so express, in some way, the species richness of the surrounding vegetation. The method adopted to test this idea was simply to transfer Fucus from one locality with an impoverished flora to another with a species-poor but different vegetation, and then to quantify the effects of transference on the diversity of the epiflora.