MEPS 140:169-178 (1996)  -  doi:10.3354/meps140169

Contribution of benthic cysts to the population dynamics of Scrippsiella spp. (Dinophyceae) in Onagawa Bay, northeast Japan

Ishikawa A, Taniguchi A

In situ germination rate (cells m-2 d-1) and cyst deposition rate (cysts m-2 d-1) were monitored for Scrippsiella spp. dinoflagellates (mostly S. trochoidea) in Onagawa Bay on the northeastern Pacific coast of Japan, using a 'germinating cell trap/sampler' and sediment traps, respectively. Seasonal relationships of each rate to the abundance of vegetative cells in the water column were investigated. Germination of the cysts on the surface sediment occurred throughout the year, but the germination rate varied seasonally and was strongly correlated with temperatures of the bottom water and the sediment, indicating that temperature is a principal factor controlling germination. Blooms occurred prior to the increase in germination rate in July, indicating that bloom initiation is not necessarily a direct consequence of mass cyst germination. Seasonal changes in recruitment ratio (ratio of the germination rate to standing crops of the vegetative cell population in the water column) revealed that, compared to summer, a large part of the winter population of vegetative cells was contributed by cyst germination but increased germination during periods of warmer temperatures contributed little to the bloom population--on the contrary, spring and summer populations appeared to be largely derived from vegetative growth. Sexual reproduction and encystment of Scrippsiella spp. in natural populations seemed to be enhanced by serial, short-term depletion of nutrients during summer. Large encystment events appeared to result in bloom termination. These findings elucidate the population dynamics of Scrippsiella spp. in Onagawa Bay. An annual budget of seed population was also calculated.

Scrippsiella spp. · Cyst · Germination rate · Cyst deposition rate · Seed population

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