Effects of episodic turbulence on diatom mortality and physiology, with a protocol for the use of Evans Blue stain for live-dead determinations

Short-lived, high-intensity turbulence in aquatic environments-or episodic turbulence-has been shown to cause mortality in zooplankton, but its effects on marine phytoplankton have rarely been investigated. Episodic turbulence derives from anthropogenic and natural causes such as boat propellers, strong winds, and breaking waves. This study focused on the effects of episodic turbulence on two diatoms: Thalassiosira weissflogii and Skeletonema costatum. 45 s exposure to turbulence intensities above 2.5 cm(2) s(-3) reduced diatom abundance by up to 32% and increased the number of intact dead cells by 22%. After exposure to 4.0 cm(2) s(-3), photosynthetic efficiency decreased by 25 and 9% in T. weissflogii and S. costatum, respectively. Turbulence also caused extracellular release of optically reactive DOM and biologically important trace metals such as iron. The turbulence levels tested are comparable to those under breaking surface waves and are substantially lower than those generated by boat propellers. An improved technique using the Evans Blue stain was developed to enable visual live/dead plankton cell determinations. When used in conjunction with preservation and flow cytometry, this staining method provides a way to study phytoplankton mortality due to turbulence and other environmental stresses.