Ostreopsis ovata Fukuyo is a benthic dinoflagellate widespread from tropical to subtropical and warm
temperate coastal areas world-wide. Since the species produces palytoxin-like substances that can
accumulate in seafood, the apparent expansion of its range in recent years represents an increasing risk
for human health. This leads to the necessity of monitoring protocols that enable the rapid detection of
the presence of this microalga in environmental samples and sea-food. We developed an identification
protocol based on real-time PCR (qPCR) to detect O. cf. ovata presence in different matrices. The protocol
was proved to be able to reveal microalgal traces in both soft tissues and intervalvar liquid of mussels
exposed to O. cf. ovata in natural and experimental conditions as well as in seawater samples. O. cf. ovata
could also be detected in mussel tissues after the end of the bloom, when it was no longer detectable in
sea water. We were able to detect O. cf. ovata in copepods fed on unialgal cultures as well. Cell density
estimates based on standard curves resulted to be comparable to direct microscopical counts. The
method is therefore suitable to ascertain the origin of palytoxin-like substances in toxic seafood. In
addition, our results confirm that mussels and other predators can actually ingest O. cf. ovata cells and act
as a vector for toxin transfer through both benthic and planktonic food webs.
