Distribution of the epiphytes along the leaves of Cymodocea nodosa in the Canary Islands

The distribution of the epiphytes along the oldest leaf of shoots of Cymodo cea nodosa was studied during a two-year cycle, from June 1990 to May 1992, in terms of number of species and cover. The difference in age between the base (the youngest part) and the apex (the oldest part) of the leaves allo wed a study of the effect of the age of the host on the epiphyte community. A continuous increase in the number of species was observed along: the old est leaf of each shoot, from basal to apical segments. While the permanent epiphyte species were present everywhere, the seasonal and the occasional s pecies were concentrated on the apical segments of the leaves and the occas ional epiphytes showed their highest abundance in winter. The greatest deve lopment of the individuals, the high number of species as well as the high densities found towards the apical segments resulted in remarkable differen ces of cover along the leaves, from 0% at the basal segments to more than 6 00% reached at the apical segments in some months during the study period. The highest mean percentage cover by epiphytes on the oldest leaf of a shoo t was detected in winter while the lowest was obtained in spring-summer. Th e Rhodophyta showed a quantitative dominance of more than 90% of cover in r elation to the rest of the algal divisions, the Ceramiales and the Corallin ales being the epiphytes which mainly contributed throughout the year. Resu lts on cover and number of species of epiphytes permitted the distinguishin g of three stages of development of the epiphytic community along the leave s: initiation, transition and maturity. Annual variations in the number of species as well as in the cover of the epiphytes along the oldest leaves we re directly related to the growth rate and life-time of the leaves of Cymod ocea nodosa. During the life-time of the leaves there was no succession of species in the epiphytic community but, from basal to apical segments, the epiphyte species were more developed and abundant, and the epiphytic commun ity became more diverse.