Biogeographia vol. XX/V - 2003 (Printed October, 31312003) Marine biogeography of the Mediterranean Sea: patterns and dynamics of biodiversity Aliens — Algal introductions to European shores IVAN GUALA, MARIA MONIA FLAGELLA, NIKOS ANDREAKIS, GABRIELE PROCACCINI, W/IEBE H.C.F. KOOISTRA, MARIA CRISTINA BUIA Stzzzione Zoologiczz ‘A. Do/om’ Vi!/zz Comumzle, ./38012] Nrzpo/i (Italy) e—7mzz'[.' zncbzzizz @5271. it Key words: invasive seaweeds, ballast water, ecophysiology, phylogeography, population genetics. SUMMARY In recent years European coastal regions have experienced a sudden increase in the number of introduced marine species, both animals and plants. Many of these species spread seemingly unchecked and show a rapid increase of their biomass, which affects whole regional ecosystems. Such species are considered invasive. Increased human activities in the realm of shipping, aquaculture, aquariology, and even scientific research may be culprits. The European Community project ALI ENS currently evaluates such invasive macroalgae and their effects on coastal resources. Findings may assist coastal government agencies in establishing rules and management strategies to avoid future invasions and to mitigate the ill-effects ofallochronous species already established. A consortium ofscientists from Spain, United Kingdom, Portugal, France and Italy are currently collaborating through the study ofvarious aspects of these invaders. Research fields include monitoring, experimental ecology, ecophysiology, phylogeography, population genetics and environmental economics. The Laboratories oFBenthic Ecology and Marine Botany of the Stazione Zoologica “A. Dohrnq (SZN) at Naples are partners within this international collaboration. Here we describe the general aims of the ALIENS programme and the SZN activities within this project. INVASIVE MARINE SEAWEEDS Allochtonous species are organisms that are new in a certain area, Where they appear suddenly in consequence of range expansions or introductions. Range expansion consists of dispersal by natural mechanisms into a region where the species did not formerly exist; introduction consists of transportation by human activity (often across natural barriers) (Carlton, 1987). These species may blend in inconspicuously for long time. Unfortunately some can disperse rapidly and severely alter or disrupt local ecosystems, replacing keystone species or affecting the biodiversity otherwise. Such allochtonous species are called