Biogeographia vol. XXV - 2004 (Printed December, 30 q’ 2004) Marine Biogeography of the Mediterranean Sea: patterns and dynamics of biodiversity Floristic and biogeographic considerations about the benthic macroalgal flora in the Gulf ofTarar1to ESTER CECERE, AN TONELLA PETROCELLI Istimto Ambiente Mrz7*i7zo Costiem (MMC) — CNR. — Sezimze dzq Trznmto — Trzlrzsrogmfico q/1. Cerrzttf’, Via Roma, 3, 74100 Trmmto (Italy) e-mail: e5ter.ceeere @irzmc.cnr. it Key words: alien seaweeds, biogeography, C1111/wpn rrzcemam var. qy/irztlrzzcetz, GulfoFTaranto, Mediterranean Sea. S UMMARY A floristic research, based on both literature and collected data, was carried out on the seaweeds of the GulfofTaranto. 462 taxa determined at both a specific and an intraspecific level were found, among which 313 are Rhodophyta, 79 Phaeophyta, 70 Chlorophyra. From a biogeographic point of view, 48.7% of species belong to the Atlantic element, 14.6% to the Mediterranean element, 24.8 % to the Cosmopolitan element, 5.3 % to the Indc—Pacific element, 5.3% to the Circurntropical element and 1.4 % to the Circurnboreal one. Twelve alien species were recently collected, of which Cnulerpzz mcemwzz var. Ly/inrlmtm and .H}7merz cornutzz proved to be invasive. INTRODUCTION For a long time, the knowledge of the marine benthic communities of the Gulf of Taranto, from both floristic and vegetational points of view, has been scarce and incomplete, being this sector of the upper Ionian Sea one of the least studied area of the Central Mediterranean Sea. The first published papers date back to the end of the nineteenth century (Piccone, 1896) and the beginning of the twentieth one (Bentivoglio, 1903). Afterwards, some papers were published about the seaweeds of the coasts of both the provinces ofTaranto (Pierpaoli, 1923; 1959; 1960; Mastrorilli, 1969) and Lecce (Solazzi, 1967; 1968; 1969; Pardi et al., 1988), respectively. However, most of these papers were short notes and reported just very few species. Only starting from the second half of the Eighties, a thorough study of the phytobenthic communities of the coasts near the town ofTaranto was planned. Its aim was both to evaluate the effects of urban and industrial pollution and to