MECHANISMS OF FLUID SHEAR‐INDUCED INHIBITION OF POPULATION GROWTH IN A RED‐TIDE DINOFLAGELLATE¹

Abstract

Net population growth of some dinoflagellates is inhibited by fluid shear at shear stresses comparable with those generated during oceanic turbulence. Decreased net growth may occur through lowered cell division, increased mortality, or both. The dominant mechanism under various flow conditions was determined for the red-tide dinoflagellate Lingulodinium polyedrum (Stein) Dodge. Cell division and mortality were determined by direct observation of isolated cells in 0.5-mL cultures that were shaken to generate unquantified fluid shear. Larger volume cultures were exposed to quantified laminar shear in Couetteflow chambers (0.004-0.019 N и m Ϫ 2 shear stress) and to unquantified flow in shaken flasks. In these larger cultures, cell division frequency was calculated from flow cytometric measurements of DNA и cell Ϫ 1 . The mechanism by which shear inhibits net growth of L. polyedrum depends on shear stress level and growth conditions. Observations on the isolated cells showed that shaking inhibited growth by lowering cell division without increased mortality. Similar results were found for early exponential-phase cultures exposed to the lowest experimental shear stress in Couetteflow chambers. However, mortality occurred when a late exponential-phase culture was exposed to the same low shear stress and was inferred to occur in cultures exposed to higher shear stresses. Elevated mortality in those treatments was confirmed using behavioral, morphological, and physiological assays. The results predict that cell division in L. polyedrum populations will be inhibited by levels of oceanic turbulence common for near-surface waters. Shear-induced mortality is not expected unless shear-stress levels are unusually high or when cellular condition resembles late exponential/stationary phase cultures.

Improvement in growth and toxin production of Alexandrium tamarense by two-step culture method

“…In early growth phase with lower cell density, static and mild agitation methods were beneficial to growth, but continuous agitation or aeration had an adverse effect on cell growth to some extent. It seemed that cells in early growth phase were very sensitive to turbulence produced by bubbling, especially by continuous aeration (Juhl & Latz, 2002). Davies et al (1986) have demonstrated that the effect of flow shear produced by agitation on cell propagation was related to intermittent flow.…”

“…Dinoflagellates are more fragile and sensitive to shear stress than other microalgae. The adverse effects caused by excess turbulence on the growth of dinoflagellate species observed in several studies (Estrada & Berdalet, 1998;Juhl & Latz, 2002; presents a challenge to the culture and production of sensitive microalgae (Parker et al, 2002).…”

Motility and autotoxicity inKarenia mikimotoi(Dinophyceae)

“…Wind strength tends to be inversely related to bloom maintenance (Yamamoto & Seike 2003). Small scale physical-biological interactions may have different effects on dinoflagellates, including lowering the growth rate (Pollingher & Zemel 1981;Juhl & Latz 2002;Sullivan et al 2003), associated sometimes with increased mortality and changes in morphology (Berdalet 1992). However, the thresholds for the appearance of such negative effects are species specific (Sullivan et al 2003).…”

Bioluminescent response of individual dinoflagellate cells to hydrodynamic stress measured with millisecond resolution in a microfluidic device

“…The main species investigated was Lingulodinium polyedrum (Stein) Dodge 1989, one of the most well-studied dinoflagellates in terms of general biology (Lewis and Hallett, 1997) and flow responses (Latz et al, 1994;Juhl et al, 2000;Juhl and Latz, 2002;Latz et al, 2004a;Latz et al, 2004b). L. polyedrum is a coastal species, 35 μm in diameter (Kamykowski et al, 1992), that is responsible for extensive blooms (Harrison, 1976;Gregorio and Pieper, 2000) with dramatic nighttime displays of bioluminescence (Latz and Rohr, 2005 …”