Harmful microalgae can produce potent toxins that cause acute mortality in humans and aquatic animals. Because the occurrence of toxic or harmful algal blooms (HABs) tends to be acute and results quickly in shellfish poisoning events or mass mortalities of aquatic organisms, emphasis has been on studying their short-term effects. The chronic harm from biotoxins produced by planktonic or benthic microalgae to aquatic animals or humans is relatively unknown. Some microalgal biotoxins have been experimentally demonstrated to act as tumor promoters in mammals. The prevalence of tumors in aquatic animals has steadily been increasing on a worldwide basis for the last 30 years, yet biotoxins are rarely considered as potential tumorigenic agents. Because there is no information on the fate and effects of natural tumor-promoting compounds in aquatic systems there has been little focus in this area.

Fibropapillomatosis (FP) in green turtles Chelonia mydas is a debilitating, neoplastic disease that has reached worldwide epizootic levels. FP has been reported principally from tropical areas in the Atlantic Ocean, the Indo-Pacific Region, the Pacific Ocean, and the Caribbean Sea. The etiology of FP is unknown but has been linked to oncogenic viruses. Toxic benthic dinoflagellates (Prorocentrum spp.) are not typically considered tumorigenic agents, yet they have a worldwide distribution, principally tropical, and produce a tumor promoter, okadaic acid (OA). Prorocentrum spp. are epiphytic on macroalgae and seagrasses that are normal components of green turtle diets. In the Hawaiian Islands, we recently demonstrated that green turtles consume substrates with Prorocentrum, and that high-risk FP areas are associated with areas where P. lima and P. concavum are both highly prevalent and abundant. The presence of presumptive OA in the tissues of Hawaiian green turtles further suggests exposure and a potential role for OA in the etiology of FP.