Seasonal and vertical distribution of marine epiphytic algae in the Evoikos Gulf (Aegean Sea, Greece)

Abstract

The subtidal epiphytic communities of both macroalgae and microalgae of the Aegean Sea have been inadequately investigated. In this paper epiphytic algal assemblages thriving on different hosts [i.e. the phaeophyte Padina pavonia (L.) LAMOUROUX, the chlorophyte Halimeda tuna (ELLIS et SOLANDER) LAMOUROUX and the seagrass Posidonia oceanica (L.) DELILE], were studied in a typical oligotrophic site of the Aegean Sea (Dikastika, Attica Peninsula) during the course of one year (June 1997-May 1998). A total of 47 taxa of epiphytic macroalgae were identified, with Hypnophyceae and Ephemerophyceae being the dominant life forms. The major algal groups (rhodophytes, phaeophytes, chlorophytes) showed a distinct seasonality, with rhodophytes predominating on all hosts. The majority of epiphytes favoured a certain position on the host thallus or blade. A distinct vertical zonation pattern was found, with epiphytes covering only certain host areas (upper-, middle-, lower parts of the plant), and further differentiated between the frond edge and blade's lamina. A total of 175 taxa of diatoms were identified and the diatom assemblages bear great resemblance to typical epiphytic floras, with dominant genera Mastogloia, Amphora, Nitzschia, Diploneis, Navicula and Cocconeis. Mass development of epiphytic diatoms on certain hosts implies host preference, but no host-specificity could be ascertained. The total epiphytic species composition seems to be affected by the seasonal alteration of abiotic factors. Epiphytic macroalgal species abundance and diversity was the highest during spring, having a possible competitive influence on the epiphytic diatom growth, whereas higher species abundance of diatoms during summer might furthermore be attributed to the surface increase of macroalgae.