looks like large cell amphidinium dinoflagellates, but i don't see the characteristic "beak" in that picture, although, it is a bit blurry. UV would also not help this form of dino's as they tend to live in the sandbed and not in the water column.
looks like large cell amphidinium dinoflagellates, but i don't see the characteristic "beak" in that picture, although, it is a bit blurry. UV would also not help this form of dino's as they tend to live in the sandbed and not in the water column.