Recurrent high-biomass blooms of Alexandrium taylorii (Dinophyceae), a HAB species expanding in the Mediterranean

Abstract

Summer outbreaks of the dinoflagellate Alexandrium taylorii Balech are recurrent events in nearshore waters of Sicily (Italy)-a central region in the Mediterranean Sea-producing dense yellowish-green patches. Beyond the local phenomenon, the problem covers a broader geographic scale, involving also other European localities, mostly in Spain. Biological, environmental, and molecular data are reported here from a semi-closed bay of Sicily (Vulcano Island, Tyrrhenian Sea, 2000-2003), showing in summer the recurrence of high-biomass blooms and events of water discolouration. Without underestimating the setbacks to the tourism industry, the ecological impact of A. taylorii blooms may be important considering the high levels of biomass produced (West Bay, Vulcano: up to a magnitude order of 107 cells l-1, 50-180 μg-Chla l-1, June 2002 and 2003) and coincident conditions of oxygen supersaturation of the waters (130-170%). Trophic trends in the Tyrrhenian site indicate high amounts of nutrients linked to the increased anthropogenic activity in summer, although recently there has been an apparent shift of the marked eutrophic conditions towards a slighter eutrophy. Genetic data on isolates of A. taylorii from the Mediterranean Sea are also discussed. Molecular analyses implied the sequencing of target rDNA regions (5.8S rDNA and ITS regions) of several isolates from different Mediterranean localities, as well as the application of species-specific PCR assays for rapid species identification in preserved field samples. The confirmation of the specific identity provided new insights into the biogeography of this species and further evidence of the occurrence of A. taylorii in a number of Mediterranean localities, both in the western side (the Catalan coast of Spain) and the eastern area (Greece). Analyses of the molecular diversity of geographically distinct isolates of A. taylorii from Italy, Spain, and Greece based on the 5.8S rDNA-ITS region sequences showed a high level of similarity, indicating the existence of an unique Mediterranean population

Taxon-specific analysis of growth and mortality rates of harmful dinoflagellates during bloom conditions

“…It should be noted that La Fosca and Vulcano beaches are situated in highly urbanized areas and Tarragona harbor receives freshwater inflows from the River Francolí. There were few cases of a potential nutrient limitation in these areas and the blooms were not conditioned by nutrients (Giacobbe et al 2004.…”

Improved phylogenetic resolution of toxic and non-toxic Alexandrium strains using a concatenated rDNA approach

“…LBA that may have earlier placed faster evolving species basally (Kim et al, 2005;Leaw et al, 2005;Montresor et al, 2004;. Phylogenetic inferences based solely on 5.8S rDNA and ITS regions extenuate this problem (Giacobbe et al, 2007;Masseret et al, 2009;Penna et al, 2008). The Alexandrium ITS regions are difficult to align correctly, and are therefore more suited to species identification rather than phylogenetic inference e.g.…”

Analysis of rRNA gene content in the Mediterranean dinoflagellate Alexandrium catenella and Alexandrium taylori: implications for the quantitative real-time PCR-based monitoring methods

“…Widespread blooms of Alexandrium catenella and A. taylori have been described over the last decade along the Spanish, French and Italian coasts (Giacobbe and Yang 1999;Vila et al 2001;Penna et al 2005). A. taylori can be found in the natural environment in high cell densities (>10 6 cells L −1 ; Garcés et al 1999;Penna et al 2002;Giacobbe et al 2007) and toxin production was demonstrated in vitro by Emura et al (2004) and in Malaysia waters (Lim et al 2005). …”