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 Cymodocea 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 allowed 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 oldest leaf of each shoot, from basal to apical segments. While the permanent epiphyte species were present everywhere, the seasonal and the occasional species were concentrated on the apical segments of the leaves and the occasional epiphytes showed their highest abundance in winter. The greatest development of the individuals, the high number of species as well as the high densities found towards the apical segments resulted in remarkable differences of cover along the leaves, from 0% at the basal segments to more than 600% 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 shoot was detected in winter while the lowest was obtained in spring-summer. The Rhodophyta showed a quantitative dominance of more than 90% of cover in relation to the rest of the algal divisions, the Ceramiales and the Corallinales being the epiphytes which mainly contributed throughout the year. Results on cover and number of species of epiphytes permitted the distinguishing of three stages of development of the epiphytic community along the leaves: initiation, transition and maturity. Annual variations in the number of species as well as in the cover of the epiphytes along the oldest leaves were directly related to the growth rate and life-time of the leaves of Cymodocea 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 community became more diverse.