G. carolinianus has tested positive for MTX using a human erythrocyte bioassay (Holland et al. 2013)
Holland, W.C., Litaker, R.W., Tomas, C.R., Kibler, S.R., Place, A.R., Davenport, E.D. & Tester, P.A. (2013). Differences in the toxicity of six <i>Gambierdiscus</i> (Dinophyceae) species measured using an <i>in vitro</i> human erythrocyte lysis essay. <em>Toxicon 65: 15-33.</em>