Análisis del entorno

This Ph.D. thesis gives novel contributions to the ecological knowledge of potential harmful algal species (HAS) in Sardinian aquatic ecosystems. New molecular data on different taxa and from different kinds of environments were provided, supporting and/or clarifying the data obtained with classical research approaches. The used techniques were developed relatively recently. We applied the PCR (with 28S and ITS-5.8S rDNA as genetic markers) on fixed samples, on cultures obtained from phytoplankton cells or germination of resting cysts, on single cells from natural samples and germinated from cysts. These techniques allowed to obtain insights on specific issues, identified as study cases.

In particular, the considered studied cases were:

- on the biodiversity of the potential toxic dinoflagellate genus Alexandrium, in Sardinian marine and transitional environments. Species belonging to this genus, in the last decade, have caused eight harmful algal blooms in Sardinian mussel farms (Giacobbe et al., 2003a; Lugliè et al., 2003a, 2003b, 2004, 2011), causing alarm for human health and economic losses. In this thesis, new data on the presence and toxicity of several Alexandrium species (namely, A. minutum, A. tamarense and A.

catenella) along the Sardinian coasts were obtained analysing new isolates from Olbia, Alghero and Santa Giusta Lagoon (chapter Ia). New isolates of A. catenella, A.

tamarense and A. minutum, from cysts germination or from vegetative cells growth from different marine coastal ecosystems, have been analysed (Chapter Ia). A.

minutum had been involved in many toxic blooms in Sardinian shellfish farming areas during the last decade. The new strains considered in this thesis were obtained from vegetative cells isolation from samples collected in the Gulf of Olbia, the main shellfish farming site in Sardinia. The obtained results give useful support to the new emerging theories about the A. minutum-group morphology and phylogeny on a global scale. A.

tamarense strain derived from a cyst germination isolated from the sediments collected in the Gulf of Alghero. Until 2008, all Mediterranean strains were grouped in a single lineage (on the base of nucleotide sequences of 5.8S gene and Internal

Transcribed Spacer regions of the rRNA operon), considered non-toxic. Therefore, this species was considered harmless in the Mediterranean basin for a long time. Penna et al. (2008) for the first time reported the detection of toxic strains from Porto Torres harbour. Consequently, the new A. tamarense strain analyzed in this study allowed deepening knowledge about the presence of toxic and non-toxic strains in the Sardinian coast. Also A. catenella strain was obtained from the germination of a cyst taken from Santa Giusta Lagoon’s sediment. This is the first report of this species in a Sardinian lagoon. Its detection in an area out of the normal monitoring for toxic algae in shellfish farming areas emphasizes the potential risk of toxic events linked to the harvesting of wild shellfishes. This result was a part of a wider study on dinoflagellate cysts composition in Mediterranean coastal lagoons and contributed to increase the global knowledge on cyst producing dinoflagellates in transitional ecosystems (chapter Ib);

- on the identification of potential harmful raphidophytes species present during past bloom events coinciding with fish kills in Santa Giusta Lagoon. The retrospective analysis on fixed archived samples with Lugol’s iodine old up to twenty years, allowed to assess the presence of C. subsalsa in coincidence of these harmful events (chapter II). On-going studies, integrating long-term ecological data available for this lagoon (which is part of the LTER-Italy network), will offer further detailed scenarios on the environmental conditions accompanying these events. Further, they will offer the opportunity to model Chattonella blooms to improve the capabilities to predict and/or to mitigate them, with a better management of the affected environments;

- on the presence and distribution of potential HAS in the poorly studied beach environments, which represent areas of high economic interest due to tourism. Also in this case, molecular methods supported species identification, and were decisived for new reports of species whose geographical distribution is not yet well known. They also have permitted to increase information on species distribution. In particular, the more frequent and/or abundant species were Alexandrium taylorii, Barrufeta bravensis, Gymnodinium instriatum and Ostreopsis cf. ovata (chapter III). These species

can affect water quality and human health, with negative impacts on the recreational function of the beaches, requiring particular attention in their touristic exploitation;

- finally, this thesis reports the preliminary results of a study on dinoflagellates blooms in Mediterranean reservoirs, considering the Sardinian artificial lakes, Sos Canales and Cedrino (chapter IV). In fact, even if Cyanobacteria are considered the most harmful group in freshwater environments, other phytoplankton component can affect water quality, conferring for example unpleasant odours and tastes, and increasing water treatment costs. Numerous difficulties have been met in the application of molecular methods to Lugol’s iodine fixed samples, collected during blooms and in the germination of cysts isolated from the sediments. SEM analysis allowed identify as a Peridiniopsis species (likely, P. penardii) the armoured red tide dinoflagellate of the Cedrino Lake, while biomolecular analyses have determined as a Gymonodium species (most probably G. uberrimum, as supposed on the morphological features) the naked dinoflagellate from Sos Canales Lake. The absence of registered sequences for freshwater Gymnodinium in Genbank not allowed confirm species attribution.