Alexandrium catanella Cyst Dynamics in a Coastal Embayment: Temperature Dependence of Dormancy, Germination, and Bloom Initiation

Alexis Fischer, Ph.D., 2017
Donald Anderson, Advisor

Blooms of the dinoflagellate Alexandrium catenella cause paralytic shellfish poisoning syndrome and present an expanding public health threat. They are inoculated through the germination of benthic cysts, a process that is regulated by internal and environmental factors, most importantly temperature. This thesis characterizes the temperature-dependence of both dormancy and germination in natural A. catenella cyst populations from Nauset Marsh (Cape Cod, MA, USA), a small estuarine embayment, and relates these processes to bloom phenology there. Through laboratory germination assays, it is shown that dormant A. catenella cysts require a quantifiable amount of chilling to exit dormancy and attain quiescence (i.e. become germinable). A series of experiments demonstrates that in situ emergence rates of A. catenella increase linearly with temperature and are comparable to germination of quiescent cysts under constant laboratory conditions. Total emergence fluxes were much lower than expected, indicating that germination occurs in a much shallower layer of surface sediments than typically assumed. A final study develops a temperature-dependent model to examine the sensitivity of A. catenella bloom phenology to dormancy-breaking by winter chilling. Notably, the chilling-alleviated dormancy model accurately predicted the onset of quiescence (January) and variable bloom phenology from multiple blooms in Nauset. Ecologically, dormancy-breaking by a chilling threshold is advantageous because it prevents the mismatch between conditions that are favorable for germination but not for the formation of large blooms. The dormancy mechanism characterized here may be present in other cyst-forming dinoflagellates, but there is likely plasticity that reflects the temperature regime of each habitat.