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Structure and replication cycle of a virus infecting climate-modulating alga Emiliania huxleyi
No full textThe globally distributed marine alga Emiliania huxleyi has cooling effect on the Earth’s climate. The population density of E. huxleyi is restricted by Nucleocytoviricota viruses, including E. huxleyi virus 201 (EhV-201). Despite the impact of E. huxleyi viruses on the climate, there is limited information about their structure and replication. Here, we show that the dsDNA genome inside the EhV-201 virion is protected by an inner membrane, capsid, and outer membrane. EhV-201 virions infect E. huxleyi by using fivefold vertices to bind to and fuse the virus’ inner membrane with the cell plasma membrane. Progeny virions assemble in the cytoplasm at the surface of endoplasmic reticulum–derived membrane segments. Genome packaging initiates synchronously with the capsid assembly and completes through an aperture in the forming capsid. The genome-filled capsids acquire an outer membrane by budding into intracellular vesicles. EhV-201 infection induces a loss of surface protective layers from E. huxleyi cells, which enables the continuous release of virions by exocytosi
A biosensor monitoring approach for toxic algae: Construction of calibration curves to infer cell numbers in field material
No full textA variety of shellfish toxin-producing Harmful Algal Blooms (HABs) occur every year in coastal temperate waters worldwide. These toxic HABs may cause lengthy (months) harvesting bans of mussels and other suspension feeding bivalves exposed to their blooms. To safeguard public health and the shellfish industry, European Union regulations request periodic monitoring of potentially toxic microalgae in seawater and phycotoxins in live bivalve molluscs from shellfish production areas. Monitoring of other toxic microalgae, e.g., fish killers, is based solely on cell counts. Morphological identification and quantification of microalgal cells with light microscopy is time-consuming, requires a good expertise, and accurate identification to species level (e.g., Pseudo-nitzschia species) may require electron microscopy. Toxicity varies among morphologically similar species; there are toxic and non-toxic strains of the same species. Molecular techniques using ribosomal DNA sequences offer a possibility to identify and detect precisely the potentially toxic genus/species. In an earlier project (MIDTAL), specific probes against rRNA sequences of all HAB taxa, known at the time of the project, affecting shellfish areas worldwide were designed, and those affecting Europe were tested and calibrated against rRNA extracts of clonal cultures and field samples. Microarray technology was adopted to relate to cell numbers the fluorescence signal from the reaction of all target species probes spotted in the microarray slides with those present in a single sample extract. The EMERTOX project aimed to develop a more automatic “Lab on a chip” (LOC) technology, including a non- (cell) disruptive water concentration system and biosensors for HAB cells detection. Here, calibration curves are presented against toxic microalgae (cultures and field samples) causing endemic and emerging toxicity events in Galicia (NW Spain) and Portugal. Results here relating cell numbers to electrochemical signals will be used in an early warning biosensor for toxic alga
Drone imagery and deep learning for mapping the density of wild Pacific oysters to manage their expansion into protected areas
Get PDFThe recent expansion of wild Pacific oysters already had negative repercussions on sites in Europe and has raised
further concerns over their potential harmful impact on the balance of biomes within protected areas. Monitoring their colonisation, especially at early stages, has become an urgent ecological issue. Current efforts to monitor wild Pacific oysters rely on “walk-over” surveys that are highly laborious and often limited to specific areas of easy access. Remotely Piloted Aircraft Systems (RPAS), commonly known as drones, can provide an effective tool for surveying complex terrains and detect Pacific oysters. This study provides a novel workflow for automated detection, counting and mapping of individual Pacific oysters to estimate their density per square meter by using Convolutional Neural Networks (CNNs) applied to drone imagery. Drone photos were collected at low tides and altitudes of approximately 10 m across a variety of cases of rocky shore and mudflats scenarios. Using object detection, we compared how different Convolutional Neural Networks (CNNs) architectures including YOLOv5s, YOLOv5m, TPH-YOLOv5 and FR-CNN performed in the detection of Pacific oysters over the surveyed areas. We report the precision of our model at 88% with a difference in performance of 1% across the two sites. The workflow presented in this work proposes the use of grid maps to visualize the density of Pacific oysters per square meter towards ecological management and the creation of time series to identify trends
Magnesium hydroxide addition reduces aqueous carbon dioxide in wastewater discharged to the ocean
Get PDFOcean alkalinity enhancement (OAE) reduces the concentration of dissolved carbon dioxide (CO2) in seawater, leading to atmospheric carbon dioxide removal (CDR). Here we report laboratory experiments and a field-trial of alkalinity enhancement through addition of magnesium hydroxide to wastewater and its subsequent discharge to the coastal ocean. In wastewater, a 10% increase of average alkalinity (+0.56 mmol/kg) led to a 74% reduction in aqueous CO2 (−0.41 mmol/kg) and pH increase of 0.4 units to 7.78 (efficiency 0.73 molCO2/mol alkalinity). The alkalinization signal was limited to within a few metres of the ocean discharge, evident as 27.2 μatm reduction in CO2 partial pressure and 0.017 unit pH increase, and was consistent with rapid dilution of the alkali-treated wastewater. While this proof of concept field trial did not achieve CDR due to its small scale, it demonstrated the potential of magnesium hydroxide addition to wastewater as a CDR solution
Carbon export from seaweed forests to deep ocean sinks
Get PDFThe coastal ocean represents an important global carbon sink and is a focus for interventions to mitigate climate change and meet the Paris Agreement targets while supporting biodiversity and other ecosystem functions. However, the fate of the flux of carbon exported from seaweed forests—the world’s largest coastal vegetated ecosystem—is a key unknown in marine carbon budgets. Here we provide national and global estimates for seaweed-derived particulate carbon export below 200 m depth, which totalled 3–4% of the ocean carbon sink capacity. We characterized export using models of seaweed forest extent, production and decomposition, as well as shelf–open ocean water exchange. On average, 15% of seaweed production is estimated to be exported across the continental shelf, which equates to 56 TgC yr−1 (range: 10–170 TgC yr−1). Using modelled sequestration timescales below 200 m depth, we estimated that each year, 4–44 Tg seaweed-derived carbon could be sequestered for 100 years. Determining the full extent of seaweed carbon sequestration remains challenging, but critical to guide efforts to conserve seaweed forests, which are in decline globally. Our estimate does not include shelf burial and dissolved and refractory carbon pathways; still it highlights a relevant potential contribution of seaweed to natural carbon sinks
Model exploration of microplastic effects on zooplankton grazing reveal potential impacts on the global carbon cycle
Get PDFAmongst the increasing number of anthropogenic stress factors threatening ocean equilibrium, microplastics (MP; <5 mm) have emerged as particularly worrisome. In situ observations have
shown that MP accumulate in large areas at the surface ocean where it may threaten the functioning marine species. In particular, experimental evidence has shown that the grazing rates of several zooplankton species may be significantly altered by MP. These direct impacts on zooplankton may
alter nutrient and carbon cycling. However, how these laboratory results may translate into impacts on the global ocean is yet unknown. Here, we use a global coupled physical-biogeochemical model including MP (NEMO/PISCES-PLASTIC) to investigate the impacts of MP exposure on zooplankton grazing rates. Drawing from experimental results, we use varying water
contamination impact thresholds to explore the biogeochemical consequences of MP impacts on short (10 years) and long timescales (100 years). Our simulations show that the geographical extent of MP impacts on zooplankton remains restricted to about 10% of the global ocean surface, even
after 100 years of constant MP contamination. However, in the most contaminated regions (e.g. the sub-tropical gyres), [MP] has surged from a few mg m−3 to >50 mg m−3 . Despite their
oligotrophic nature and limited contribution to the overall ocean carbon cycle, MP impacts on zooplankton grazing could disrupt carbon cycling in these highly contaminated regions (up to 50% reduction in yearly primary production, carbon export fluxes and organic matter remineralisation after 100 years). Our research suggests that persistent MP pollution in the ocean could diminish primary production by 4%. In spite of the large sensitivity of our results to the water contamination impact threshold, we suggest MP impacts on zooplankton grazing may cause an annual loss of 1 Gt yr−1 of exported carbon after 100 years, if MP inputs remain constant globally
Collapse of a giant iceberg in a dynamic Southern Ocean marine ecosystem: In situ observations of A-68A at South Georgia
Get PDFLarge icebergs (>20 km long) are responsible for most of the freshwater discharged into the Southern Ocean. We report on in situ and satellite observations made during the break-up phase around South Georgia of the giant tabular iceberg A-68A. The in situ measurements were obtained during a 4-day visit by a research vessel in February 2021, where physical, chemical and biological measurements were made at a range of distances away
from the main and subsidiary icebergs. These results were compared to a far-field station 133 km away. Up�stream of the iceberg field, water column structure was similar to ambient water although there was evidence of iceberg-associated phytoplankton as a likely remnant of the passage of the icebergs. Nevertheless, enhancement of primary productivity along the path of the icebergs was not resolved in either in situ or monthly mean satellite observations. There was a considerable brash-ice field moving ahead of the icebergs which limited the number of downstream sampling stations. One downstream station within 2 km of iceberg A-68P showed several ice-melt influenced features that distinguished it from most other stations. Firstly, there was a strong stratified meltwater influenced layer that reached to around 120 m. This had the effect of deepening underlying water masses, with
the core of the temperature minimum layer around 50 m deeper than elsewhere. Secondly, there was evidence of rapid downward displacement of both particulate material and certain phytoplankton taxa that may be a further result of this water mass deepening. Thirdly, macronutrient profiles were altered, with concentrations of nitrate, silicic acid and phosphate characteristic of deeper layers being found closer to the surface and a dilution of the ambient nutrient pool just above the iceberg draft that we ascribe to meltwater released from basal melting. Meanwhile, nutrient recycling processes associated with organic matter remineralisation were also modified by the physical restructuring of the water column and biotic components. Finally, the ice-associated phytoplankton
taxa Pseudo-nitszchia/Nitszchia, found in both upstream and downstream locations, were abundant at this < 2 km-distant station through melting out from the iceberg and subsequent rapid growth. Overall, we resolved alterations to water column structure, nutrient profiles and phytoplankton community composition at fine to medium scales around the iceberg field. Nevertheless, although there may have been longer term and larger scale impacts, the dynamic oceanographic environment, including the presence of a strong oceanographic front and
shelf-edge processes, dominated during the collapse of A-68A
Gathering users and developers to shape together the next-generation ocean reanalyses: Ocean reanalyses workshop of the European Copernicus Marine Service
No full textOcean reanalyses are reconstructions of the past ocean state combining ocean numerical models and earth observations through data assimilation techniques. As a result of their temporal and spatial consistency and continuity compared to earth observations only, and their high accuracy and quality compared to pure numerical model simulations, ocean reanalysis data are widely used in the scientific community (e.g., ocean and climate process studies) and private sectors (e.g., operational planning, shipping, and fisheries). For almost a decade, the Copernicus Marine Service has provided users with high-quality, regularly extended global and regional ocean reanalyses. The objective of this workshop was to gather the international community to (1) understand the users’ needs for ocean reanalyses, (2) identify the strengths and weaknesses of current ocean reanalyses, and (3) establish the way forward toward the
next generation of ocean reanalyses by improving different aspects of these products to meet users' needs and science ambitions (4) improve collaborations within the
community. The three-day workshop was held in Toulouse (France) and brought together ocean reanalysis users, producers from European Copernicus services and beyond, and
scientific experts on different aspects (data assimilation, ocean models, and observations). The workshop’s hybrid format (online and in person) enabled us to
welcome around 60 people in person and 1400 registrations online, with 700 unique connections on day one, 350 on day two, and 250 on day three. The key findings of each objective are given in the following sections; the last section highlights the next steps the ocean reanalyses community will carry out
Linking ecosystem pressures and marine macroinvertebrate ecosystem services in mangroves and seagrasses
No full textOcean warming and acidification, decreases in dissolved oxygen concentrations, and changes in primary production are causing an unprecedented global redistribution of marine life. The identification of underlying ecological processes underpinning marine species turnover, particularly the prevalence of increases of warm-water species or declines of cold-water species, has been recently debated in the context of ocean warming. Here, we track changes in the mean thermal affinity of marine communities across European seas by calculating the Community Temperature Index for 65 biodiversity time series collected over four decades and containing 1,817 species from different communities (zooplankton, coastal benthos, pelagic and demersal invertebrates and fish). We show that most communities and sites have clearly responded to ongoing ocean warming via abundance increases of warm-water species (tropicalization, 54%) and decreases of cold-water species (deborealization, 18%). Tropicalization dominated Atlantic sites compared to semi-enclosed basins such as the Mediterranean and Baltic Seas, probably due to physical barrier constraints to connectivity and species colonization. Semi-enclosed basins appeared to be particularly vulnerable to ocean warming, experiencing the fastest rates of warming and biodiversity loss through deborealization
Steeper size spectra with decreasing phytoplankton biomass indicate strong trophic amplification and future fish declines
Get PDFUnder climate change, model ensembles suggest that declines in phyto�plankton biomass amplify into greater reductions at higher trophic levels, with
serious implications for fisheries and carbon storage. However, the extent and
mechanisms of this trophic amplification vary greatly among models, and
validation is problematic. In situ size spectra offer a novel alternative, com�paring biomass of small and larger organisms to quantify the net efficiency of
energy transfer through natural food webs that are already challenged with
multiple climate change stressors. Our global compilation of pelagic size
spectrum slopes supports trophic amplification empirically, independently
from model simulations. Thus, even a modest (16%) decline in phytoplankton
this century would magnify into a 38% decline in supportable biomass of fish
within the intensively-fished mid-latitude ocean. We also show that this
amplification stems not from thermal controls on consumers, but mainly from
temperature or nutrient controls that structure the phytoplankton baseline of
the food web. The lack of evidence for direct thermal effects on size structure
contrasts with most current thinking, based often on more acute stress
experiments or shorter-timescale responses. Our synthesis of size spectra
integrates these short-term dynamics, revealing the net efficiency of food
webs acclimating and adapting to climatic stressor