Diversity of epiphytic diatom flora on Mediterranean seagrasses: morphological aspects and ecological role

DIVERSITY OF EPIPHYTIC DIATOM FLORA ON MEDITERRANEAN SEAGRASSES: MORPHOLOGICAL ASPECTS AND ECOLOGICAL ROLE M. DE STEFANO (1,2), D.Marino (2), L. Mazzella (1) Stazione Zoologica di Napoli. (1) Laboratorio di Ecologia del Benthos, 80077 Ischia (NA), (2) Laboratorio di Botanica Marina, Villa Comunale, 80100 Napoli The aim of the present work was to characterize the epiphytic diatom flora on seagrass leaves and to assess their role in such important ecosystems. Of the different mediterranean seagrasses, such as Posidonia oceanica, Cymodocea nodosa and Zostera noltii, highest diatom species richness and diversity was recorded on P. oceanica, due to the greater surface area for colonization and the complexity of microhabitats. The most frequently encountered diatoms were the genera Cocconeis, Gomphonemopsis, Fragilaria,. Mastogloia and Navicula, belonging to different “growth forms”. In Cymodocea and Zostera the diatom flora was meanly characterized by the Cocconeis group. Diatom abundances reached densities as high as 3000 cells/mm2 in Posidonia and 8000 in Cymodocea; in Zostera diatoms were at times the only recorded flora with concentrations up to 2500 cells/mm2. The biomass of the Cocconeis group, dominant in all seagrasses, was highest in P. oceanica (1,3 mgC/sh-1), due to the large leaf canopy. Due to its diversity and abundance, the epiphytic diatom flora largely contribute to the production of the seegrass systems and to the grazing activity of mesoherbivores living in the meadows.