Microscale Patches of Nonmotile Phytoplankton

Abstract

Phytoplankton cells have evolved sophisticated strategies for actively responding to environmental signals, most notably to mechanical stresses of hydrodynamic origin. A largely unanswered question, however, is the significance of these cellular responses for the largely heterogeneous spatial distribution of cells found in the oceans. Motivated by the physiological regulation of buoyancy prevalent in nonmotile phytoplankton species, we solve here a minimal model for "active" sinking that incorporates these cellular responses. Within this model, we show how buoyancy regulation leads to intense patchiness for nonmotile species as compared to passive tracers, resulting in important variations in settling speeds and, as a consequence, determining escape rates to the deep ocean.

Dynamics of phytoplankton blooms in turbulent vortex cells

“…More recent work suggests that such trapping is only possible if more complex flow structures are considered [48]. Nevertheless, even if sedimentation of cells occurs continuously, the persistence of a viable population ultimately depends on relation of phytoplankton growth and sedimentation [7], an argument that is supported by model studies [18,49].…”

“…Under these conditions phytoplankton concentrations are homogeneous in the horizontal dimension and the highest concentrations are either found at the surface or at the bottom of the domain. It is worth noting, however, that we only considered passively sinking cells at a constant rate, while mobile phytoplankton, in particular gyrotaxis [11], as well as variable sinking rates [49], have been shown to influence spatial distribution and intensive patchiness. In fact, phytoplankton cells have been shown to react to turbulent cues by altering their swimming direction in order to avoid exposure to highly turbulent layers [51].…”

Phototaxis beyond turning: persistent accumulation and response acclimation of the microalga Chlamydomonas reinhardtii

“…The fitness of microorganisms depends critically on their ability to sense dynamic physico-chemical clues from the environment, elaborate the information and respond effectively. Environmental responses range from changes in gene expression [1] (typical timescale ∼ 10 min); to the activation/deactivation of biochemical processes like chloroplast photoprotection [2] (∼ 1 min); to fast movement regulation (∼ 1 s), either active [3,4] or passive [5]. The best characterised motile response is currently chemotaxis of run-and-tumble bacteria like E. coli [6], a strategy based on the modulation of tumbling frequency [7].…”

Physical and ecological processes at a moving ice edge in the Fram Strait as observed with an AUV

“…Accumulation of plankton at frontal systems is a known feature which, besides physical processes, is also affected by the ability of growing phytoplankton to stay positively or neutrally buoyant (e.g. Smayda, 1970;Franks, 1992;Acuña et al, 2010;McManus and Woodson, 2012;Prairie et al, 2012;Arrieta et al, 2015). As a consequence, phytoplankton is not purely advected like a passive tracer, as positively buoyant organisms withstand the flow of water to a certain degree.…”