Long-term observations on the intertidal lichen Lichina pygmaea Ag.

Abstract

In a previous paper (Boney, 1961) an account was given of some experiments and observations carried out on the lichen Lichina pygmaea Ag. growing above M.T.L. on the east-facing side of the Church Reef (= Blackstone Rocks) at Wembury, South Devon. The experiments were initiated in the summer and autumn of 1952 and 1953. Experimental sites were prepared by removing rectangular areas of lichen growth from within larger mats, and by clearing away half the lichen growth from small circular patches of about 10 cm diameter. Subsequent observations were re-ported after intervals of 4–7 years (to July 1960). The more obvious results of the clearances made within lichen mats were the failures of the surrounding plant growths to recolonize the cleared areas after 4 years and the disappearance of lichen cover from the borders of one of the cleared areas. The presence of Fucus spiralis L. plants growing in mats near cleared areas indicated that the damage inflicted on the lichen growths had set in train an irreversible series of events. With small circular patches of about 10 cm diameter cleared of half their lichen cover no changes were observable after seven years in both the cleared areas and in the remaining lichen growth. Since 1963 my visits to the experimental sites have been somewhat sporadic. The present note describes observations made up to July 1976, 24 years after initiation of the first clearance experiments.