New records of intensive blooms of Alexandrium minutum (Dinophyceae) in the Jonian Sea, Italy

In Italy Alexandrium minutum is recurrently found at low concentrations in mussel farming
areas, such as the Western Adriatic and the Sardinia coasts; mussels positive to PSP toxins have
occasionally been detected but rarely exceeded the legal limit for commercial sale. Conversely,
in South Italy, the Sicilian coast represents a hot spot of A. minutum blooms, repeatedly occurring
in high densities. This study shows the presence of extensive blooms detected for the first time
on the Jonian coast of Calabria at Roccella Jonica; the first bloom occurred in 2018, followed
by a larger event in 2020. Both blooms occurred in March in the harbour dockyard, an area not
monitored for toxic algae due to the absence of mussel farms. The blooms caused a yellow/brown
water discoloration, but no PSP symptoms were reported. In order to understand if these blooms
can cause harmful consequences, five Alexandrium strains were isolated from the 2018 event
for molecular identification at the species level and analysis of the toxin content and profile. All
strains were confirmed to belong to the A. minutum group and produce PSP toxins, with four
out of five clones displaying higher toxin levels. The toxin profile displayed slight differences
among strains, however, GTX 1,4 were the prevalent analogues, as previously observed in the
Mediterranean region. Despite A. minutum blooms being rare events historically, intensive toxic
blooms are increasing, especially on the South Italian coasts. This poses some concerns and
highlights the need for better monitoring and management of the new identified spot and of
nearby areas.