Dynamic sinking behaviour in marine phytoplankton: rapid changes in buoyancy may aid in nutrient uptake

Abstract

Phytoplankton sinking is an important property that can determine community composition in the photic zone and material loss to the deep ocean. To date, studies of diatom suspension have relied on bulk measurements with assumptions that bulk rates adequately capture the essential characteristics of diatom sinking. However, recent work has illustrated that individual diatom sinking rates vary considerably from the mean bulk rate. In this study, we apply high-resolution optical techniques, individual-based observations of diatom sinking and a recently developed method of flow visualization around freely sinking cells. The results show that in both field samples and laboratory cultures, some large species of centric diatoms are capable of a novel behaviour, whereby cells undergo bursts of rapid sinking that alternate with near-zero sinking rates on the timescales of seconds. We also demonstrate that this behaviour is under direct metabolic control of the cell. We discuss these results in the context of implications for nutrient flux to the cell surface. While nutrient flux in large diatoms increases during fast sinking, current mass transport models cannot incorporate the unsteady sinking behaviour observed in this study. However, large diatoms appear capable of benefiting from the enhanced nutrient flux to their surface during rapid sinking even during brief intervening periods of near-zero sinking rates.

Coupling Water Column and Sediment Biogeochemical Dynamics: Modeling Internal Phosphorus Loading, Climate Change Responses, and Mitigation Measures in Lake Vansjø, Norway

“…Although this version of MyLake adds NO 3 − and NH 4 + as state variables, it does not yet simulate N-limitation to algal growth or phytoplankton community dynamics, as is done in other models such as PROTECH (Reynolds et al, 2001); thus, community shifts due N recycling from the sediments, or to changing climate, are not captured. Other processes, such as cell buoyancy effects (Gemmell et al, 1840) and grazing by zooplankton (George & Reynolds, 1997), are also not included.…”

Bistability in oxidative stress response determines the migration behavior of phytoplankton in turbulence

“…To cope with turbulence, phytoplankton can regulate lipid content, release of infochemicals, or gene expression profiles (13). On faster timescales, phytoplankton are able to respond to the fluid mechanical cues associated with turbulence (14) by regulating buoyancy (15) or switching migratory direction (16). In particular, some dinoflagellates and raphidophytes alter their direction of vertical migration when exposed to the periodic changes of orientation relative to gravity caused by turbulent eddies, leading to the emergence of a downward-migrating subpopulation among cells originally migrating upward (16).…”

A computational continuum model of poroelastic beds

“…That is, we assume that the macroscale global Δ P relates to the characteristic Young's modulus of the solid skeleton as follows: $\frac{\mathrm{normal\Delta }P}{E}\le \mathcal{O}false(ϵfalse).$ This assumption holds in many engineering configurations, where elastic properties of materials are often of order MPa or GPa, while the pressure difference generated by moving fluids is commonly of order kPa (in wind tunnel experiments, for example). It also holds for many biological systems; the elasticity moduli are of order MPa or kPa [54–56], where biological materials are often exposed to much slower fluid flows [57] and consequently smaller fluid forces.…”