Spatio-temporal variability and association of diatom-dinoflagellate assemblages of Acanthophora, Hypnea and Gracilaria (Rhodophyta)

Epiphytic microalgae can significantly affect the host seaweed either by complementing, or competing for, resources. Here, epiphytic diatom and dinoflagellate species assemblages on the macroalgae Acanthophora spicifera, Hypnea pannosa and Gracilaria salicornia collected during the north-east (February), inter- (April) and south-west (June) monsoons in 2015 along the coast of Lucero, Pangasinan, North-western Philippines were examined and characterized. Results showed that diatom-dinoflagellate assemblages strongly clustered by season rather than by geographic location. Within season, a minor clustering by macroalgal forms, rather than host species identity, was also observed, which could be associated with the differences in the complexity and texture of the upright and prostrate seaweeds. Examination of the 'thallisphere' using confocal laser scanning microscopy further revealed the close proximity of some of the 'resident' epiphytic species to the cortical cells of the host, causing deformities and implying more complex interactions. Our results suggest that epiphytic community assemblages were influenced by both the environmental conditions associated with seasonal variation and the microhabitats in the surface of the different algal forms.