First record of Ostreopsis cf. ovata bloom and its ovatoxins in Libyan Mediterranean coastal waters

Ostreopsis cf. ovata is a benthic dinoflagellate, which is largely distributed in marine environment worldwide, including Mediterranean Sea coastal areas. Its blooms are frequently linked to noxious effects on human health and marine organisms due to the production of potent toxins termed ovatoxins. This study reports the presence of Ostreopsis cf. ovata bloom for the first time in Libyan Mediterranean coastal waters. The cell density of O. cf. ovata in Tajoura waters was 1.7 × 10³ cells L⁻¹ before the bloom event, and sharply increased and formed an intense bloom (1.6 × 10⁵ cells L⁻¹) on September 19, 2023. The bloom lasted four days and suddenly collapsed, most likely as a result of a change in environmental conditions, leaving no O. cf. ovata cells in the seawater. The occurrence of O. cf. ovata bloom positively correlated with water temperature (r = 0.9), salinity (r = 0.8) and nutrient concentrations (nitrogen and phosphorus; r = 0.8–0.9) in Tajoura waters. Furthermore, bloom field samples and a cultured strain of O. cf. ovata produced a toxin profile of palytoxin analogues dominated by ovatoxin-a (39.7 pg cell⁻¹) ovatoxin-b (8.1 pg cell⁻¹). The study identified a new health risk in the area and suggested the occurrence of more toxic dinoflagellates in the future, most likely as a result of climate change. Therefore, harmful algal species should be regularly monitored along the whole Mediterranean coast of Libya. Additionally, it is imperative to evaluate the levels of ovatoxins in locally harvested seafood to protect the public from consuming such potent toxins.