like other dinoflagellates, "alexandrium monilatum" has wide swings in population size. when concentrations rise, algal blooms occur and fish can be killed by the ichthyotoxin, goniodomin a identified in both "a. monilatum" and "a. pseudogoniaulax". secondary toxic substances produced by this species include saxitoxins and gonyautoxins. toxic red tides caused by this species have caused large fish kills off the coasts of texas, florida and venezuela. this dinoflagellate does not cause mortality in adult shellfish but does reduce nutritional uptake as well as increasing mortality in larvae.