Diel vertical migration of Peridiniopsis niei, Liu et al., a new species of dinoflagellates in an eutrophic bay of Three-Gorge Reservoir, China Yaoyang Xu • Qinghua Cai • Lan Wang • Linghui Kong • Daofeng Li Received: 9 January 2009 / Accepted: 9 November 2009 / Published online: 27 November 2009 Ó Springer Science+Business Media B.V. 2009 Abstract In spring, a typical dinoflagellate (Peridini- opsis niei Liu et al.) constitutes most of the phytoplankton biomass in most of eutrophic bay of Three-Gorge Reservoir (TGR, China). There are few field observa- tions on vertical migration of the members of the genus Peridiniopsis. We studied diel vertical migration of the new species (Peridiniopsis niei) at sampling stations A and B in an eutrophic bay (Xiangxi Bay) of TGR during both day and night in March 2007. The present study suggests that vertical migration by Peridiniopsis niei is similar in nature to the migration patterns observed for other dinoflagellates. Solar irradiance incident was an important factor regulating the ascent and descent of Peridiniopsis niei. The vertical descent of Peridiniop- sis niei during nighttime was restricted when the thermocline (Temperature gradient [ 1°Cm -1 ) was present in the station B. Keywords Diel vertical migration  Dinoflagellate  Thermocline  Incident solar radiation  Nutrient  Stratification Introduction Dinoflagellates are a diverse group of unicellular or colonial eukaryotic microorganisms, which are char- acterized by regulated motility combined with an ability to photosynthesize (Clegg et al. 2007). As an important functional component of the phytoplankton community, most of the dinoflagellates are capable of using their weak swimming abilities to perform diel vertical migration (DVM), which is a widespread phenomenon in both marine and freshwater habitats, and it has been the focus of most migration studies (Salonen and Rosenberg 2000; Beckmann and Hense 2004; Townsend et al. 2005; Doblin et al. 2006; Yamamoto and Nakahara 2006). In general, DVM behavior is known to facilitate the cells acquiring both high light and high nutrient levels, by maintain- ing near surface distributions by day and near pycnocline and nutricline depths by night (Ralston et al. 2007; Ross and Sharples 2008). Advantages of DVM behavior can be used to explain the dominance of dinoflagellates in marine and freshwater ecosystem (Salonen and Rosenberg 2000; Clegg et al. 2004; Townsend et al. 2005; Doblin et al. 2006). Most of dinoflagellates with high light and high nutrient affinities frequently become the principal contributor to harmful algal blooms and red tides (Erga et al. 2003; Bearon et al. 2006). Knowledge of DVM is of fundamental importance in explaining dinoflagellates bloom in marine and freshwater habitats and under- standing the ecology of dinoflagellates. Y. Xu  Q. Cai (&)  L. Wang  L. Kong  D. Li State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, 430072 Wuhan, People’s Republic of China e-mail: qhcai@ihb.ac.cn Y. Xu  L. Wang  L. Kong Graduate University of Chinese Academy of Sciences, 100049 Beijing, People’s Republic of China 123 Aquat Ecol (2010) 44:387–395 DOI 10.1007/s10452-009-9298-8