[2] The bloom in 2006 off Sant Andreu de Llavaneres in northeastern Spain, was described as "a conspicuous, thick, brownish mucilage layer covering benthic macroalgae".

[6] It is now postulated that the substance is synthesized by the dinoflagellates and is subsequently incorporated into the zoanthid tissues; it may be a symbiotic arrangement, and it is possible that bacteria are involved in the transfer.

[7] Species of Ostreopsis have been implicated in outbreaks of ill health in countries to the immediate north of the Mediterranean Sea, particularly Spain, Italy and Greece.

[8] These symptoms have been shown to be the result of aerosols containing the dinoflagellates, which had been whipped off the surface of the water by winds, and carried ashore to the detriment of public health.

[4][9] In a separate incident, a mass mortality of the sea urchin Evechinus chloroticus occurred in New Zealand in 2004, associated with a bloom of O. siamensis, although in this instance there were no human casualties.