Epiphytic diatoms on Gelidiales (Rhodophyta) from Gran Canaria (Spain)

The composition and patterns of spatial and season variability of epiphytic diatom assemblages of five intertidal species of Gelidiales (Rhodophyta) from three sampling sites off Gran Canaria (Canary Islands, Atlantic Ocean) were investigated during summer (2007) and winter (2008) seasons using scanning electron microscopy (SEM). Dominant species included Cocconeis scutellum var. scutellum, C. scutellum var. posidoniae, Grammatophora oceanica, Lichmophora eherembergi, Navicula sp. and Tabularia fasciculata and these represented 78% of the total diatom assemblage on Gelidiales. Eight of the diatom taxa, Cocconeis maxima, Amphicocconeis debesii, Cocconeis convexa, C. neothumensis var. marina, C. scutellum var. scutellum, C. scutellum var. posidoniae, Gomphonemopsis obscura and Pseudohimantidium pacificum, found in the present study represent new records for the Canary Archipelago. These species showed two distinct patterns of zonation, one in relation to their position at the intertidal area and the other relative to position on the host thalli. Although the vertical distribution of host thalli at the intertidal zone was important when considering the assemblage structure of epiphytic diatoms, the results showed that the cell abundance distribution changed more significantly when considering season rather than spatial distribution. Moreover, even though morphology of host thalli was not a determining factor, their aggregation mode had a significant influence on the abundance and distribution of microalgae. Finally, considering the growth forms of diatom communities, adnate diatoms were more abundant in turf than in clump species.