This species is capable of diel vertical migration in the water column (Olli 1999).
Heterocapsa rotundata is a dinoflagellate commonly found in estuarine waters.
H. rotundata is known to be transported around the world in ballast water (Pertola et al. 2006).
H. rotundata has a largely global distribution in coastal environments.
Like many small, dinoflagellates capable of photosynthesis, H. rotundata often blooms after the spring diatom bloom. The slower growth rates and higher nutrient half-saturation constants of phototrophic dinoflagellates contributes to the lag of the dinoflagellate bloom behind the diatom bloom. In addition, the nutrients released from the dying diatom bloom can fuel the subsequent dinoflagellate bloom. Blooms of H. rotundata are not known to be toxic, but can discolor the water with a reddish tint.
H. rotundata is a small, unarmoured, gymnodinoid dinoflagellate. It is easily identified by its "mushroom" shape (epitheca is twice as large as the hypotheca).
H. rotundata is usually found in the water column in estuarine environments.
Heterocapsa rotundata is a known mixotroph, capable of photosynthesis and heterotrophic feeding. It has been observed feeding on Skeletonema costatum in the laboratory at the rate of 0.007 ng C per cell per day at a prey concentration of 259 cells per mL (Yeong et al. 2009) and Synechococcus (Jeong et al. 2005). This species can also feed on bacteria and has been observed doing so in the field at rates that rival heterotrophic nanoflagellates (Seong et al. 2006). During blooms, H. rotundata can have a significant impact on marine bacteria populations.
H. rotundata is preyed upon by other mixotrophic dinoflagellates, such as Pfiesteria piscicida (Jeong et al. 2006) and ciliates, such as Mesodinium pulex (Jakobsen et al. 2006).
