PRIMARY ADHESION OF ENTEROMORPHA (CHLOROPHYTA, ULVALES) PROPAGULES - QUANTITATIVE SETTLEMENT STUDIES AND VIDEO MICROSCOPY

Quantitative methods and associated kinetic analyses have been used fo r the first time to study detailed aspects of tile settlement and adhe sion of various types of Enteromorpha propagule. Time course experimen ts showed that quadri- and biflagellate zoospores and zygotes adhered rapidly, but a proportion within any one population appeared to be inc ompetent at adhering to the substratum. Kinetic (Scatchard) analysis o f adhesion experiments performed at a range of zoospore concentrations revealed density-dependent effects not previously reported, with posi tive cooperativity at low spore densities and negative cooperativity a t high spore densities. High-resolution video microscopy was used for the first time to reveal details of the various stages in the settleme nt and adhesion of zoospores and zygotes. Novel observations were made of an, initial, temporary phase of attachment via the apical papilla, followed by a permanent phase of commitment, characterized by dischar ge of adhesive-containing cytoplasmic vesicles, as the cell contracted against the surface, and adsorption of flagella. The Phase of commitm ent was followed by exploitation of the surface through amoeboid-like movements at the interface. Gregarious settlement behavior was frequen tly observed leading to the formation of rafts of cells. The possible mechanisms and significance of density-dependent spore adhesion are di scussed.