Program

Many HABs are caused by species that form resting cysts that facilitate survival through environmental extremes such as cold winters or nutrient-limitation, with the transitions between life stages determining timing and duration of blooms. Predictions of the response of cyst-forming species to climate change are difficult given complex internal and external regulatory mechanisms for encystment and excystment. One way to address these complexities is through natural weather perturbations and oceanographic anomalies that mimic potential climate change scenarios. Here we describe the response of Alexandrium fundyense to two such anomalies. One was a shift in water mass properties in the Gulf of Maine (2010), leading to surface waters that were warmer, fresher, more stratified, and with lower than normal nutrients. There was no bloom because cysts (controlled by an internal clock) germinated into waters that were not supportive of growth and bloom development. The second example is from a shallow estuarine system where the winter and spring of one year (2012) was several degrees warmer than those of other years. Such warming has been hypothesized to increase the duration of the “window” of permissive temperatures, promoting earlier and long-lasting blooms. Indeed, the bloom began one month early, but it terminated one month earlier as well; the total duration was not different from other years. Together, these results suggest that the mechanisms by which some cyst-forming species regulate encystment and excystment may be so finely tuned to their habitats that the effects of warming are less straightforward than simply an expanded bloom window.  This also highlights the difficulties in predicting an organism’s response to future climate change scenarios within complex ecological and hydrodynamic systems.