Macroalgal epiphytes of Posidonia oceanica leaves: biogeographic aspects

Abstract

Biogeographia vol. XXI V - 2003 (Printed October, 31st 2003) Marine biogeography of the Mediterranean Sea: patterns and dynamics of biodiversity Macroalgal epiphytes of Posidonia oceazniccz leaves: biogeographic aspects ANNUNZIATA ESPOSITO, AURORA ULISSE, IVAN GUALA, MARIA CRISTINA BUIA Srzzzione Zoologiaz 1/I. Do/am’ Bent/air Ecology Lzz/aomrmfy — P.ta San Pietro 80077131/9721, Nzzpoli (Italy) E-mzzil: mc[7uz'zz@szn.z't Key words: epiphytes, spatial patterns, biogeographic groups, Pasizlorrizz ocemzim. SUMMARY Epiphyte summer assemblages of Poridazzizz ocezzuim leaves were analyzed at regional (Sardinia) and basin (\X/estern Mediterranean Sea) scales. Along Sardinian coasts, species composition has been evaluated at different sides (East and West), depths (5 and 25 m), and geographical sectors (North, Central—North, Central-South and South), in a total of32 sites. Deriving data from literature, five localities at the same depth were compared, at basin scale. The community structure, at both taxonomic and biogeographic level. was analyzed to reveal spatial patterns in epiphyte assemblages. At smaller scale, the number of species varied significantly with side, sector and site, while the assemblage composition did not; the biogeographic composition did not show significant differences because of the relevant influence of Subcosmopolitan and Cosmopolitan taxa. At basin scale taxonomic and biogeographic composition of epiphyte communities did not change according to a latitudinal gradient at least dealing with Western central Mediterranean Sea. INTRODUCTION Epiphytic algae are a diverse flora growing on host seagrasses. Their importance to Posidonzkz ocezzrziczz ecosystem functioning in terms of food supply for macroherbivore—detritivore species is well recognized (Garnbi et al., 1992; Buia et al., 2000; Zupo, 2001). In some cases the grazing impact was found to have a stabilizing effect on the system, as the epiphytic community may negatively influence the leaf production of seagrasses (Orth and Van Montfrans, 1984). However, this latter process was never confirmed in P. ocezmiczz and it could be considered as an indicator ofenvironmental change in the functioning of the system. A predictable succession and zonation ofepiphytic taxon and assemblages are identifiable on seagrass leaves, according to the blade age—gradient and life—tirne,