The cells of Osteropsis ovata have a diameter at their largest part, about 40 micro meters, which, if we compare it to the diameter of a cyanobacteria cell (2-3 micro meters), gives us an idea of its relative size. Ostreopsis, like many other harmful dinoflagellates, secretes a large amount of mucus to build extracellular matrices, macroscopically characterized by the presence of strands and filaments, in which oxygen bubbles resulting from photosynthesis are trapped. These matrices settle on any existing substrate, sand, rocks, glasses, etc., suffocating the existing micro fauna.This can be observed, for example, when the aggregates formed on the substratum are siphoned off, revealing areas of sand with a dark gray color, indicating anaerobic bacterial activity, resulting from the depletion of oxygen produced by the layer of dinoflagellates settled on top. The extracellular matrices also serve to immobilize potential predators such as amphipods and copepods.