On the fate of sinking diatoms: the transport of active buoyancy-regulating cells in the ocean.

Diatoms are one of the most abundant, diverse and ecologically relevant phytoplanktonic group, contributing enormously to global biogeochemical processes like the carbon and silica cycles. This large success has been partly attributed to the mechanical and optical properties of the silica shell (the frustule) that envelops their body. But since they lack motility it is difficult to conceive how they cope with the fast-fluctuating environment they live in and where distributions of resources are very heterogeneous and dynamical. This pinpoints an important but yet poorly understood feature of diatoms physiology: buoyancy regulation that helps them controlling their sinking speed and position in the water column. While buoyancy regulation by light and nutrients availability has been well studied, the effect of hydromechanical stress via fluid shear has been rather overlooked when considering diatoms dynamics. Here, we aim to start filling this gap by first presenting direct experimental evidences for buoyancy control in response to hydro-mechanical stress and then review recent theoretical models where simple couplings between local shear and buoyancy control always result in heterogeneous cell distributions, specific accumulation regions within complex flows and increased sedimentation times to the depths, features of direct ecological relevance. We conclude by suggesting future experiments aiming to unveil such coupling and therefore gain better understanding on the fate of these fascinating microorganisms in their natural habitat. This article is part of the theme issue 'Stokes at 200 (part 2)'.

Nurses and Voluntary Assisted Dying: How the Australian Capital Territory's Law Could Change the Australian Regulatory Landscape.

On June 5, 2024, the Australian Capital Territory passed a law to permit voluntary assisted dying ("VAD"). The Australian Capital Territory became the first Australian jurisdiction to permit nurse practitioners to assess eligibility for VAD. Given evidence of access barriers to VAD in Australia, including difficulty finding a doctor willing to assist, the Australian Capital Territory's approach should prompt consideration of whether the role of nurses in VAD should be expanded in other Australian jurisdictions. Drawing on lessons from Canada, which currently permits nurse practitioners to assess patient eligibility, we argue that the time has come for Australian jurisdictions to expand the role of nurses in VAD systems. This would be an important step in ensuring access to VAD for patients in practice. Attention, however, must also be paid to ensuring adequate remuneration of nurses (and doctors) if this goal of promoting access is to be achieved in practice.