MORPHOLOGICAL VARIATION AND POPULATION-STRUCTURE OF FUCUS SPP (PHAEOPHYTA) FROM HELGOLAND

The greater part of the rocky eulittoral of Helgoland (North Sea/Germa n Eight) is populated by fucoids, namely Fucus spiralis, Fucus vesicul osus, and Fucus serratus. Several differences from the Fucus populatio ns of the North European mainland shores are obvious, regarding both t he population structure and form variations within the individual spec ies. In general, the Fucus species do not form distinct belts, but bui ld up mixed populations. Fucus vesiculosus occurs in two morphological ly distinct forms which cannot be attributed to particular habitat con ditions. On the average, the fronds of the Helgoland Fucus species are longer and significantly narrower than in specimens from other coasta l sites of Western Europe. The results are discussed in the context of insular endemism related to the recent geological development and geo graphic position of Hergoland.