Effect of growth conditions on flow‐induced inhibition of population growth of a red‐tide dinoflagellate

Abstract

The population growth of some dinoflagellates is known to be reduced by exposure to fluid flow. The red‐tide dinoflagellate Lingulodinium polyedrum was used to examine the effect of growth conditions on flow‐induced inhibition of population growth. Three factors were tested: time of exposure relative to the light:dark (LD) cycle, illumination level, and culture growth phase (early vs. late exponential phase). Cultures maintained on a 12:12 h LD cycle were exposed to one of two flow conditions: quantified laminar shear produced by Couette flow or unquantified flow generated in shaken flasks. The duration of exposure to flow was 1 h d−1 for 5–8 d in all experiments; the shear stress in Couette shear experiments was 0.004 N m−2. There were many qualitative similarities in the pattern of response to flow in the two hydrodynamic conditions. In both cases, exposure to flow in the last hour of the dark phase resulted in greater reduction of net growth than exposure during the light phase. Cultures grown under lower illumination had proportionally greater reductions in net growth than cultures under higher light. Finally, late exponential phase cultures exhibited much greater reductions in net growth following a given flow exposure than early exponential phase cultures. The higher sensitivity of late exponential phase cultures did not appear to be linked to nutrient limitation or changes in pH of the medium; it may be partially attributed to exudates from late exponential phase cells. These results suggest that the response of red‐tide dinoflagellate population growth to in situ turbulence may depend on both environmental conditions and the physiological state of the cells.