Effects of turbulence intermittency on growth inhibition of a red tide dinoflagellate, Gonyaulax polyedra Stein

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Abstract
Thomas and Gibson (1990a, b) quantified the rate of strain γ required to inhibit the growth of the red tide dinoflagellate Gonyaulax polyedra Stein in a Couette flow device that produces an effectively constant γ value to represent the small‐scale shear encountered by dinoflagellates in turbulent flow. A continuous γ value of about 8 rad s−1 was found to cause zero‐growth rates, >8 caused negative growth, and < 2 caused no effect. Measurements of the same organism in the same device with intermittent γ show that the daily average γ threshold for zero growth does not require continuous shear but decreases to values smaller than 0.09 rad s−1 with increasing intermittency (decreasing fraction of the time of shear application) up to a limiting minimum time period of 5–15 min. When γ values of 9 rad s−1 were applied for periods of only 2.5,1, and 0.25 hours during a day, increasingly negative growth rates were observed (although 5 min had no effect). Thus was reduced by 2 orders of magnitude by intermittency of the simulated turbulence. Because turbulence near the sea surface is intermittent, especially when waves are breaking, the effects on dinoflagellate growth inhibition will be larger and extend to much greater depths than might be expected from only the profile. Comparison with the lagged correlations of wind wave spectral components versus oceanic phytoplankton growth (Tynan, 1993), showing larger negative correlations between dinoflagellate concentration and waves than with winds, suggests a similar response exists between dinoflagellate growth inhibition in natural populations and turbulence intermittency and strength. Diatoms exhibit the opposite response, with growth enhancement.

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