Effects of Small‐scale Turbulence on Net Growth Rate and Size of Ten Species of Marine Dinoflagellates1

Field observations and results from previous laboratory studies on the effects of turbulence on dinoflagellates have led to a paradigm in phytoplankton ecology that dinoflagellate growth is negatively affected by turbulence. To test the paradigm, 10 species of autotrophic dinoflagellates were exposed to quantified three‐dimensional turbulence generated by vertically oscillating cylindrical rods in 20‐L rectangular culture tanks. Turbulence was quantified in the tanks (as the turbulent energy dissipation rate,ε) using an acoustic Doppler velocimeter. Dinoflagellates were exposed to two turbulence treatments: high turbulence (ε∼ 10−4m2·s−3), low turbulence (ε∼ 10−8m2·s−3), and an unstirred control. In accord with the paradigm,Ceratium fusus(Ehrenberg) Dujardin had lower net growth rates in high turbulence, whereasPyrocystis noctilucaMurray ex Haeckel andCeratium tripos(O. F. Müller) Nitzsch did not increase their numbers in high turbulence. However,Alexandrium tamarense(Lebour) Balech,Pyrocystis fusiformisWyville‐Thomson ex Murray,Alexandrium catenella(Whedon and Kofoid) Balech, and aGyrodiniumsp. Kofoid and Swezy were apparently unaffected by turbulence and had the same net growth rates across all turbulence treatments. Contradicting the paradigm,Lingulodinium polyedrum(Stein) Dodge (=Gonyaulax polyedra),Gymnodinium catenatumGraham, andAlexandrium fundyenseBalech had increased net growth rates in high turbulence treatments. Cross‐sectional area (CSA) varied little across turbulence treatments for 8 of 10 dinoflagellate species tested, CSA inC. fususincreased when net growth rate decreased in high turbulence, and, conversely, CSA decreased inL. polyedrumwhen net growth rate increased in high turbulence.