A transect from the rim to the inner part of a Fucus stand was simulated by connecting 5 aquaria (replicated 3 times) in a series with 1 Fucus individual in each aquaria except the first. Thus the water chemistry in the successive aquaria reflected the presence and metabolism of 0, 1, 2, 3, and 4 Fucus individuals “upstream”. The water flowing through each series stemmed from a header tank which was either acidified or not.