Toxin content of Ostreopsis cf. ovata depends on bloom phases, depth and macroalgal substrate in the NW Mediterranean Sea.

•Ostreopsis cf. ovata bloomed from late June to August 2017 at Villefranche-sur-Mer, France, Mediterranean Sea.•Ovatoxins contents were higher during the exponential and stationary growth phases.•Highest abundance was on Dictyota spp. but highest toxin quota on Halopteris scoparia.•Ovatoxin profile was not affected by the bloom phase, the depth or the macroalgae.