Journal of Applied Phycology (2005) 17: 391–401 DOI: 10.1007/s10811-005-8700-8 C  Springer 2005 Cyanobacterial blooms and water quality in Greek waterbodies Elizabeth Vardaka 1,3 , Maria Moustaka-Gouni 1 , Catherine M. Cook 2 & Tom Lanaras 1, ∗ 1 Department of Botany, Aristotle University of Thessaloniki, P.O. Box 109, GR–541 24 Thessaloniki, Greece; 2 National Agricultural Research Foundation (NAGREF), Agricultural Research Centre of Macedonia-Thrace, P.O. Box 60458, GR-570 01 Thermi, Greece; 3 Present address: Department of Fisheries and Aquaculture Technology, Technological Educational Institute of Thessaloniki, Campus of New Moudania, P.O. Box 157, GR-632 00 New Moudania, Greece ∗ Author for correspondence: e-mail: lanaras@bio.auth.gr Received 21 March 2005; revised and accepted 7 June 2005 Key words: associations, biovolume, chlorophyll a, Microcystis, risk-assessment, toxin-producing Abstract The cyanobacterial species composition of nine Greek waterbodies of different type and trophic status was examined during the warm period of the year (May–October). Cyanobacterial water blooms were observed in all waterbodies. Forty-six cyanobacterial taxa were identified, 11 of which are known to be toxic. Eighteen species are reported for the first time in these waterbodies, 8 of which are known to produce toxins. Toxin producing species were found in all of the waterbodies and were primarily dominant in bloom formations (e.g., Microcystis aeruginosa, Anabaena flos-aquae, Aphanizomenon flos-aquae and Cylindrospermopsis raciborskii). Cosmopolitan species (e.g., M. aeruginosa), pantropic (e.g., Anabaenopsis tanganyikae) and holarctic species (e.g., Anabaena flos-aquae) were encountered. Shallow, eutrophic waterbodies had blooms dominated by Microcystis species and were character- ized by phytoplankton association M. Anabaena and Aphanizomenon species of association H were dominant in waterbodies with low dissolved inorganic nitrogen and thermal stratification in the summer. Total cyanobacterial biovolumes (CBV) ranged from 7 to 9,507 cm 3 m −3 and were higher than Alert Level 2 and Guidance Level 2 (10 cm 3 m −3 ; World Health Organization; WHO) in seven of the waterbodies. Chlorophyll a concentrations ranged from 6 to 90,000 mg m −3 and were higher than Alert Level 2 and Guidance Level 2 (50 mg m −3 ; WHO) in eight of the waterbodies. There is also an elevated risk of acute toxicosis (Guidance Level 3; WHO) in five waterbodies. Water of an undesirable quality, hazardous to humans and animals occurs in several Greek waterbodies. Abbreviations: CBV, Cyanobacterial biovolume; Chl a, Chlorophyll a; EC, European Community; EU, European Union; PCA, Principal Components Analysis; TCBV, Toxic cyanobacterial biovolume; WFD, Water Framework Directive; WHO, World Health Organization Introduction Water blooms have become a frequent phenomenon in eutrophic waterbodies worldwide as in the Mediter- ranean region. The warm Mediterranean climate favours the extended duration of the cyanobacterial blooms, which may start in spring and persist until December, or in some cases, may even be continu- ous throughout the year. Phytoplankton studies in some Greek lakes (Vegoritis, Volvi, Mikri Prespa, Doirani and Kastoria) have shown that prolonged cyanobacte- rial blooms of up to 8 months can occur, which are dominated by known toxic species (Moustaka-Gouni & Nikolaidis, 1990; Moustaka-Gouni, 1993; Tryfon & Moustaka-Gouni, 1997; Temponeras et al., 2000; Vardaka et al., 2000). Comprehensive long-term studies of phytoplankton do not exist for the majority of Greek waterbodies.