Formation of an ectocarpoid epiflora on blades of Laminaria digitata

The development of ectocarpoid algae on blades of Laminaria digitata (Hudson) Lamouroux has been followed by punching discs in a median line from proximal to distal ends of the blade, and culturing these in the laboratory for a period of 4 wk. Laminaria sporophytes were collected from exposed-shore and sheltered-shore populations on the Isle of Man (UK) but no difference could be detected either in species composition of their epifloras or in distribution and growth of ectocarpoid algae along the frond. The epiphyton was dominated by the microthallus of Ectocarpus fasciculatus, which gave rise to another generation of fertile offspring during the culture period. It is concluded that the success of E. fasciculatus may be due to its particular growth and reproductive characteristics which enable it to maintain a presence on the Laminaria blade throughout its phase of rapid growth.