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

Scrippsiella rotunda and Scrippsiellatrochoidea var. aciculifera (orderPeridiniales, subfamily Calciodinelloideae) are autotrophicorthoperidinioid dinoflagellates producing calcareous resting cysts whichare at times abundant in coastal marine sediments. We have carried outlaboratory experiments to investigate features of cyst germination in thetwo species, including dormancy length, germination pattern and germinationsuccess, over an annual cycle and under different light and temperatureconditions. The maturation period for S. rotunda cystswas between 17 and 24 weeks, while that of S.trochoidea var. aciculifera was muchshorter, ranging between 2 and 5 weeks. Both species required exposure tolight for germination, while temperature shifts (from 14 to 20C) in the dark did not induce excystment of maturecysts. In both species, germination was not synchronous, but distributedover a variable time interval, suggesting a high physiological diversitywithin the cyst pool. Moreover, exposure to light of S.rotunda cysts that had not completed maturation impaired thegermination of a great percentage of the cysts. Differences in dormancylength may partially explain the distinct cyst production patterns observedfor the two species in the Gulf of Naples.