Nitrate uptake by Karenia brevis. I. Influences of prior environmental exposure and biochemical state on diel uptake of nitrate

Abstract

) and nitrate-replete conditions (~20 μM NO 3 -) prior to the experiment. Cells exposed to nitrate-depleted environments for 12 h prior to the experiment enhanced nocturnal uptake compared to cells continuously exposed to nitrate-replete conditions. Changes in cell physiology may contribute to nitrate acquisition after descent from oligotrophic environments to areas with elevated nitrate concentrations. KEY WORDS: Karenia brevis · Dinoflagellate · Physiology · Nocturnal uptake · Vertical migrationResale or republication not permitted without written consent of the publisher

Individual-based modelling of the development and transport of a Karenia mikimotoi bloom on the North-west European continental shelf

“…10 Row 2). Observations suggest that K. mikimotoi do display vertical swimming over a limited depth range (Gentien 1998), and other Karenia species have been found to migrate to much greater depths (Liu et al, 2001;Sinclair et al, 2006). Conversely, the inclusion of depth-limited downward swimming activity made little difference to the model results.…”

“…cells can access nutrients through vertically migrating to deep shelf water (e.g. Liu et al, 2001;Sinclair et al, 2006); this mechanism is cited as the reason for high bloom densities observed in oligotrophic coastal waters (Stumpf et al, 2008). Nutrient concentrations may not, therefore, be a limiting factor in population growth, provided sufficient nutrients are available somewhere within the water column.…”

Deep-water seed populations for red tide blooms in the Gulf of Mexico

“…obs.). Another factor that may contribute to persistence of K. brevis under severe nutrient limitation is that it can also enhance its dark uptake of N to nearly daylight rates subsequent to low-nutrient exposure (Sinclair et al 2006a). Furthermore, when a K. brevis cell near the benthos receives less (Sinclair & Kamykowski 2006) than the compensation irradiance of 0.3% surface PAR (Shanley 1985, Shanley & Vargo 1993, it may become phagotrophic.…”

“…brevis is motile, performing diel vertical migrations (DVM) (van Dolah & Leighfield 1999), and adapted for both low-light (Shanley & Vargo 1993, Magaña & Villareal 2006 and low-nutrient conditions (Sinclair et al 2006a(Sinclair et al ,b, 2009, such as would be expected in offshore near-bottom water along the oligotrophic shelf of the GOM. Bloom formation has previously been assessed using surface sampling, but if these photosynthetic dinoflagellates migrate down to utilize a benthic nutrient source and bottom depth is >15 m, they are unlikely to reach the surface during their upward migration for light.…”

“…Even though the majority of the water column along the shelf of the GOM is typically oligotrophic in the upper water column (< 0.1 µmol N), and growth rates of marine plankton are typically nitrogen limited (Hecky & Kilham 1988), blooms of >10 4 cells l −1 appear to form at the surface 18 to 24 km offshore (Steidinger 1975, Tester & Steidinger 1997. K. brevis is efficient at nitrogen accumulation in low concentration conditions, indicated by its low half-saturation rate of nitrogen uptake, K s = 0.06 to 1.07 µmol N (Steidinger et al 1998, Bronk et al 2004, and can further enhance accumulation efficiency by increasing uptake rates after prior low-nutrient exposure (Sinclair et al 2006a). A variety of nitrogen forms present in porewater along the WFS and subsequently fluxing from the sediment could sustain a diffuse K. brevis population (Sinclair et al 2006b).…”