Differences in the toxicity of six Gambierdiscus (Dinophyceae) species measured using an in vitro human erythrocyte lysis assay

► Gambierdiscus species exhibit significant hemolytic activity (HA). ► HA was caused by maitotoxins and differs significantly among species. ► HA varied geographically and with growth phase. ► Intraspecies isolates obtained from the same region exhibited similar HA. ► HA (maitotoxin) was constitutively produced and under strong genetic control.