Cyst-forming dinoflagellates in a warming climate

• Published in: Harmful algae 2020-01, Vol.91, p.101728-101728, Article 101728
• Main Authors: Brosnahan, Michael L., Fischer, Alexis D., Lopez, Cary B., Moore, Stephanie K., Anderson, Donald M.
• Format: Article
• Language: English
• Subjects: Climate change; Cysts; Dinoflagellida; Harmful Algal Bloom; Humans; Microbial life cycles; Resting cyst dormancy; Shellfish Poisoning; Temperature
• ISSN: 1568-9883; 1878-1470
• DOI: 10.1016/j.hal.2019.101728

•Temperature controls dormancy cycling in dinoflagellate resting cysts.•Dormancy-climate interactions can explain HAB biogeography and phenology.•Temperature seasonality promotes resilience of resting cyst populations to warming.•Cell density dependent encystment triggers can limit bloom intensification.•Longer HABs in response to warming will reflect prolonged cyst bed quiescence. Many phytoplankton species, including many harmful algal bloom (HAB) species, survive long periods between blooms through formation of benthic resting stages. Because they are crucial to the persistence of these species and the initiation of new blooms, the physiology of benthic stages must be considered to accurately predict responses to climate warming and associated environmental changes. The benthic stages of dinoflagellates, called resting cysts, germinate in response to the combination of favorable temperature, oxygen-availability, and release from dormancy. The latter is a mechanism that prevents germination even when oxygen and temperature conditions are favorable. Here, evidence of temperature-mediated control of dormancy duration from the dinoflagellates Alexandrium catenella and Pyrodinium bahamense—two HAB species that cause paralytic shellfish poisoning (PSP)—is reviewed and presented alongside new evidence of complementary, temperature-based control of cyst quiescence (the state in which cysts germinate on exposure to favorable conditions). Interaction of the two temperature-based mechanisms with climate is explored through a simple model parameterized using results from recent experiments with A. catenella. Simulations demonstrate the importance of seasonal temperature cycles for the synchronization of cysts’ release from dormancy and are consistent with biogeography-based inferences that A. catenella is more tolerant of warming in habitats that experience a larger range of seasonal temperature variation (i.e., have higher temperature seasonality). Temperature seasonality is much greater in shallow, long-residence time habitats than in deep, open-water ones. As warming shifts species’ ranges, cyst beds may persist longer in more seasonally variable, shallow inshore habitats than in deep offshore ones, promoting HABs that are more localized and commence earlier each year. Recent field investigations of A. catenella also point to the importance of new cyst formation as a factor triggering bloom termination through mass sexual induction. In areas where temperature se