Beyond equilibrium climate sensitivity

ISSN:1752-0908ISSN:1752-089

Harmful algal blooms mitigation using clay/soil/sand modified with xanthan and calcium hydroxide

A method was studied for marine harmful algal blooms (HABs) mitigation using clay, soil, or sand modified with xanthan and calcium hydroxide. Results showed that xanthan could trap and wrap Amphidinium carterae cells via bridging and netting interactions due to its superior salt compatibility in seawater. The maximum cell removal efficiency was 55% when xanthan was used alone. The removal effect of xanthan was enhanced by the addition of appropriate calcium hydroxide that decreased the repulsive interaction between anionic xanthan and negatively charged algal cells. Three kinds of minerals (clays, soils, and sands) were ineffective in removing algal cells before treatment. When xanthan and calcium hydroxide were used together as modifiers, the removal efficiency increased to 83-89% within 30 min using 300 mg L-1 clays, soils, or sands modified with 20 mg L-1 xanthan and 100 mg L-1 calcium hydroxide. After several hours, 95-98% cell removal was achieved and there was no significant difference in the removal efficiencies among clays, soils, and sands after being modified with xanthan and calcium hydroxide. Thus, the method would provide an alternative modification approach to suppress and mitigate HABs using local soils/sands and polymers in marine systems

Global distribution and vertical patterns of a prymnesiophyte–cyanobacteria obligate symbiosis

A marine symbiosis has been recently discovered between prymnesiophyte species and the unicellular diazotrophic cyanobacterium UCYN-A. At least two different UCYN-A phylotypes exist, the clade UCYN-A1 in symbiosis with an uncultured small prymnesiophyte and the clade UCYN-A2 in symbiosis with the larger Braarudosphaera bigelowii. We targeted the prymnesiophyte–UCYN-A1 symbiosis by double CARD-FISH (catalyzed reporter deposition-fluorescence in situ hybridization) and analyzed its abundance in surface samples from the MALASPINA circumnavigation expedition. Our use of a specific probe for the prymnesiophyte partner allowed us to verify that this algal species virtually always carried the UCYN-A symbiont, indicating that the association was also obligate for the host. The prymnesiophyte–UCYN-A1 symbiosis was detected in all ocean basins, displaying a patchy distribution with abundances (up to 500 cells ml− 1) that could vary orders of magnitude. Additional vertical profiles taken at the NE Atlantic showed that this symbiosis occupied the upper water column and disappeared towards the Deep Chlorophyll Maximum, where the biomass of the prymnesiophyte assemblage peaked. Moreover, sequences of both prymnesiophyte partners were searched within a large 18S rDNA metabarcoding data set from the Tara-Oceans expedition around the world. This sequence-based analysis supported the patchy distribution of the UCYN-A1 host observed by CARD-FISH and highlighted an unexpected homogeneous distribution (at low relative abundance) of B. bigelowii in the open ocean. Our results demonstrate that partners are always in symbiosis in nature and show contrasted ecological patterns of the two related lineages.Versión del editor8,951

Strategies among phytoplankton in response to alleviation of nutrient stress in a subtropical gyre

Despite generally low primary productivity and diatom abundances in oligotrophic subtropical gyres, the North Atlantic Subtropical Gyre (NASG) exhibits significant diatom-driven carbon export on an annual basis. Subsurface pulses of nutrients likely fuel brief episodes of diatom growth, but the exact mechanisms utilized by diatoms in response to these nutrient injections remain understudied within near-natural settings. Here we simulated delivery of subsurface nutrients and compare the response among eukaryotic phytoplankton using a combination of physiological techniques and metatranscriptomics. We show that eukaryotic phytoplankton groups exhibit differing levels of transcriptional responsiveness and expression of orthologous genes in response to release from nutrient limitation. In particular, strategies for use of newly delivered nutrients are distinct among phytoplankton groups. Diatoms channel new nitrate to growth-related strategies while physiological measurements and gene expression patterns of other groups suggest alternative strategies. The gene expression patterns displayed here provide insights into the cellular mechanisms that underlie diatom subsistence during chronic nitrogen-depleted conditions and growth upon nutrient delivery that can enhance carbon export from the surface ocean