Effects of phytoplankton physiology on export flux

Abstract

Estimates of phytoplankton sticking efficiency (α) were made in the laboratory within a 1500 l annular flume mesocosm over the initiation, maintenance and senescence phases of a bloom of the diatom Thalassiosira pseudonana. The spatially weighted mean turbulence kinetic energy dissipation rate in the annular flume was comparable to values found at the ocean's surface on a calm day. The α of T. pseudonana varied as a result of physiological state, and ranged from 0 ± 0.08 during the bloom initiation to 0.26 and 0.73 ± 0.16, respectively, during bloom maintenance and senescence phases. During the periods of high α, physiological changes included (1) diminished phytoplankton photosynthetic quantum efficiency, (2) an increase in super-oxide dismutase protein expression, reflecting oxidative stress, and (3) the induction of a biochemical cascade initiating autocatalytic programmed cell death. Additionally, during the period of high physiological stress on the diatoms, there was an increase in the presence of transparent exopolymer particles and bacteria. Applying a variable α to a 1-dimensional export flux model shows that carbon export can be increased by at least 2-fold compared to simulations assuming a typically modeled value of α = 1 (100% sticking efficiency). The model using a physiologically dependent α had a low initial sticking efficiency that allowed a significant increase in the critical concentration of algal cells. Such an increase in the number of cells during bloom initiation followed by an increase in α during the maintenance and senescence phases resulted in enhanced export fluxes during the latter, 'stickier', stages of the bloom.

Abundance and size distribution of transparent exopolymer particles (TEP) in a coccolithophorid bloom in the northern Bay of Biscay

“…Several studies have shown that the balance between TEP and solid particles, such as cells, co-determines the efficiency of particle coagulation and formation of macroscopic aggregates (Logan et al, 1995;Engel, 2000;Kahl et al, 2008). Particle aggregates are a major vehicle for organic matter export to the deep ocean.…”

Can Hydrodynamics Change Phosphorus Strategies of Diatoms?—Nutrient Levels and Diatom Blooms in Lotic and Lentic Ecosystems

“…Thus, the mechanisms behind diatom dominance in lentic and lotic water might not be identical because hydrodynamic conditions may differ between these types of systems. Thus, the flow regime should be considered as a prerequisite inducement for diatom blooms in natural water bodies [13,28].…”

Diatom-associated bacteria are required for aggregation of Thalassiosira weissflogii

“…Release of exudates by diatoms is species-specific and depends on environmental conditions (Myklestad, 1995;Kahl et al, 2008). In laboratory experiments, three different types of aggregation behavior were distinguishable: (i) non-aggregating species that produce very little TEP (for example, Thalassiosira weissflogii), (ii) aggregating species that generate a cell coating of sticky TEP-like material but produce no free TEP (for example, Nitschia angularis) and (iii) species that generate copious amounts of TEP and form TEP-rich aggregates (for example, Chaetoceros sp.)…”