Assessment of harmful algal species using different approaches: the case study of the Sardinian coasts

The presence and distribution of harmful algal species were investigated along the coasts of Sardinia in the summer of 2012. Fourteen potentially noxious taxa were identified at 74 beaches. The majority of the recovered taxa were potentially toxic and/or high biomass producers. <i>Alexandrium taylorii</i>, <i>Gymnodinium instriatum</i>, and <i>Ostreopsis</i> cf. <i>ovata</i> were the most frequent and abundant taxa, although <i>Barrufeta bravensis</i> reached the highest density (4.4 × 10⁶ cells L⁻¹). <i>Barrufeta bravensis</i>, <i>A. taylorii</i>, and <i>G. instriatum</i> were responsible for intense water discoloration at two of the beaches sampled. Polymerase chain reaction (PCR) analyses supported the identification of several taxa and decisively identified <i>B. bravensis</i>. PCR assays increased the information available on the species distributions. The locations studied were heterogeneous in their prevailing environmental conditions and their morphodynamic profiles. Statistical analyses indicated that the distributions of harmful algal species correlated with gravel and medium-fine sand substrata. These data provide substantial knowledge on the distributions of harmful algal species on beaches, which have been poorly studied on a global scale. The apparent relationship between noxious species and grain size suggests that vegetative cells may be recruited from cyst beds in beach sediments.