How viable are cysts of the harmful alga Alexandrium catenella from a “seed bed” in Puget Sound?

Alexandrium catenella is a single-celled harmful alga that can produce a range of potent neurotoxins when it blooms. Shellfish concentrate these toxins from the water during filter feeding, and consumption of contaminated shellfish can impact wildlife and can also cause a severe illness in humans called paralytic shellfish poisoning (PSP). The life cycle of A. catenella involves a benthic overwintering cyst stage and a planktonic motile stage. Areas with high concentrations of resting cysts on the seafloor are called “seed beds” and are potential bloom initiation sites. To develop predictive bloom models for local forecasting, a better understanding of A. catenella life history characteristics is necessary; specifically, the processes governing cyst germination and bloom initiation. Using the Most Probable Number (MPN) method, the percentage of viable cysts and the rate of germination were each determined at 14°C and 20°C for the Quartermaster Harbor “seed bed” in Puget Sound. The number of viable cysts in the 0-1 cm layer was compared to the total number of cysts determined by primuline-stained counts of cysts in the same sample. All of the cysts in the sediment sample were capable of germinating at 20°C whereas 15% of cysts were capable of germinating at 14°C. The rates at which cysts germinate were also found to be temperature dependent, with a faster germination rate as temperature increases. These data suggest that temperature may affect both cyst germination capability and rate. Understanding the relationship between cyst germination and temperature can facilitate more accurate analysis of existing benthic cyst distribution data, as well as improving the sourcing of blooms from “seed beds.