Study of dinoflagellate life cycle and its role in population dynamics.

摘要

Scrippsiella narragansettensis sp. nov. from Greenwich Cove, Narragansett Bay, USA is described with light and scanning electron microscopy. A small orthoperidiniod dinoflagellate, it is lacrimiform and photosynthetic with a plate formula: Po, x, {dollar}rm 4prime, 3a, 7primeprime, 6c, 5s, 5primeprimeprime, 2primeprimeprimeprime.{dollar} Its right sulcal plate bears a large triangular list covering the sulcal area. Its spherical cyst has long slender capitate spines, which are made partly of calcareous material. Three other Scrippsiella species are also examined.; Scrippsiella narragansettensis, S. spinifera and S. trochoidea have been studied in culture at various temperature and nutrient levels. They each have their specific temperature range to grow optimally and produce cysts. Nitrogen deficiency is most efficient in inducing cyst formation in all three species, followed by phosphorus deficiency. Cysts of S. narragansettensis and S. trochoidea both have a short mandatory dormancy period of less than two weeks. Cysts of S. narragansettensis genninate better and more quickly at low temperatures than at high temperatures. Cysts of S. trochoidea germinate better and more quickly at high temperatures than at low temperatures. Temperature, light, and length of incubation might play a similar and complementary role in the cyst maturation of S. narragansettensis and S. trochoidea. Their species-specific responses to variations in water temperature and nutrient levels might explain their seasonality observed in Greenwich Cove.; A two-year investigation with weekly samplings in Greenwich Cove shows that S. narragansettensis, S. cf. rotunda, S. spinifera, S. trochoidea, Polykrikos schwartzii, Protoperidinium leonis, Protoperidinum oblongum, and Preperidinium meunieri were the major cyst-forming dinoflagellates. Cysts were commonly produced in situ, sometimes in significant numbers, in late spring and summer. There was little difference in the spatial and temporal (1995 vs. 1996) pattern in cyst production. However, the magnitude of cyst production varied. Time-series analysis shows that in most cases, in situ cyst production was correlated with their respective motile population with a lag of one week. It is suggested that the seasonal variation in cyst production was primarily correlated with abundance of motile cells. Dinoflagellates in the water column were affected by other factors such as water temperature and nutrient concentration.