Different excystment patterns in two calcareous cyst-producing species of the dinoflagellate genus Scrippsiella

Abstract

Scrippsiella rotunda and Scrippsiella trochoidea var. aciculifera (order Peridiniales, subfamily Calciodinelloideae) are autotrophic orthoperidinioid dinoflagellates producing calcareous resting cysts, which are at times abundant in coastal marine sediments. We have carried out laboratory experiments to investigate features of cyst germination in the two species, including dormancy length, germination pattern and germination success, over an annual cycle and under different light and temperature conditions. The maturation period for S.rotunda cysts was between 17 and 24 weeks, while that of S. trochoidea var. aciculifera was much shorter, ranging between 2 and 5 weeks. Both species required exposure to light for germination, while temperature shifts (from 14 to 20°C) in the dark did not induce excystment of mature cysts. In both species, germination was not synchronous, but distributed over a variable time interval, suggesting a high physiological diversity within the cyst pool. Moreover, exposure to light of S.rotunda cysts that had not completed maturation impaired the germination of a great percentage of the cysts. Differences in dormancy length may partially explain the distinct cyst production patterns observed for the two species in the Gulf of Naples.