Abstract: Climate change induced alterations of oceanic conditions will lead to the ecological niches of some marine phytoplankton species disappearing, at least regionally. How will such losses affect the ecosystem and the coupled biogeochemical cycles?

Here, we couch this question in terms of ecological redundancy (will other species be able to fill the ecological roles of the extinct species) and biogeochemical redundancy (can other species replace their biogeochemical roles). Prior laboratory and field studies point to a spectrum in the degree of redundancy. We use a global three-dimensional computer model with diverse planktonic communities to explore these questions further. The model includes 35 phytoplankton types that differ in size, biogeochemical function and trophic strategy. We run two series of experiments in which single phytoplankton types are either partially or fully eliminated.

The niches of the targeted types were not completely reoccupied, often with a reduction in the transfer of matter from autotrophs to heterotrophs. Primary production was often decreased, but sometimes increased due to reduction in grazing pressure. Complex trophic interactions (such as a decrease in the stocks of a predator’s grazer) led to unexpected reshuffling of the community structure. Alterations in resource utilization may cause impacts beyond the regions where the type went extinct.

Our results suggest a lack of redundancy, especially in the ‘knock on’ effects on higher trophic levels. Redundancy appeared lowest for types on the edges of trait space (e.g. smallest) or with unique competitive strategies. Though highly idealized, our modelling findings suggest that the results from laboratory or field studies often do not adequately capture the ramifications of functional redundancy. The modelled, often counterintuitive, responses - via complex foodweb interactions and bottom-up versus top-down controls - indicate that changes in planktonic community will be key determinants of future ocean global change ecology and biogeochemistry. 

Abstract: The net balance between photosynthesis and respiration in the surface ocean is a key regulator of ocean‐atmosphere CO₂ partitioning, and by extension, Earth's climate. The slight excess of photosynthesis over community respiration in sunlit waters, known as net community production (NCP), sets the upper bound on the sequestration of carbon via biological pump export. Prevailing paradigms suggest a high/low binary where net primary production (NPP), NCP, and export are highest in ecosystems characterized by microplankton (>20 μm) and lowest in ecosystems dominated by picoplankton (<2 μm). This bifurcation model neglects the potential importance of nanoplankton (2‐20 μm) – i.e. the “middle” size class – toward global biological pump functioning.

Here, we show a relationship between the biomass of nanoplankton and oxygen‐based estimates of NCP across natural ecological gradients in the North Pacific Ocean. Using a suite of high‐resolution optical imaging approaches including SeaFlow, Imaging FlowCytobot, and laser‐based scattering, nanoplankton dynamics are observed to dominate the particle size distribution throughout a ~1000 km transition between the subtropical and subpolar North Pacific, where NCP rates are 3 to 5‐fold higher than subtropical values.

Based on ecological theory applied to the Darwin size‐based ecosystem model, we hypothesize that intermediate size‐class organisms are capable of high rates of production via an optimization of bottom‐up and top‐down control inherent to the ‘middle class’. More broadly, the model indicates the global importance of nanoplankton for ocean biological production.

Summary: ​An interdisciplinary analysis of human interactions with mercury through history that sheds light on efforts to promote and achieve sustainability.

In Mercury Stories, Henrik Selin and Noelle Eckley Selin examine sustainability through analyzing human interactions with mercury over thousands of years. They explore how people have made beneficial use of this volatile element, how they have been harmed by its toxic properties, and how they have tried to protect themselves and the environment from its damaging effects. Taking a systems approach, they develop and apply an analytical framework that can inform other efforts to evaluate and promote sustainability.

After introducing the framework, which uses the lens of a human-technical environmental system and a matrix-based approach to analyze mercury use and exposure, the authors examine five topical mercury systems that each illustrate important issues in mercury science and governance: global cycling of mercury through the atmosphere, land, oceans, and societies; mercury's dangers to human health, including from occupational, medical, and dietary exposure; mercury emissions to the atmosphere from industrial sources; mercury in commercial products and production processes; and mercury use in artisanal and small-scale gold mining. Finally, looking across the five mercury systems, they distill insights for sustainability analysis more broadly, and draw lessons for researchers, decision-makers, and concerned citizens.