• Energy Research

AbstractIn the Western Tropical South Pacific, a hotspot of dinitrogen‐fixing organisms has been identified. The survival of these species depends on the availability of dissolved iron (DFe); however, the source of this DFe is still unclear. DFe was measured along a transect from 175°E to 166°W near 19–21°S. The distribution of DFe showed high spatial variability: low concentrations (∼0.2 nmol kg−1) in the South Pacific gyre and high concentrations (up to 50 nmol kg−1) in the west of the Tonga arc, indicating that this arc is a clear boundary between iron‐poor and iron‐rich waters. An optimal multiparameter analysis was used to distinguish the relative importance of physical transport relative to non‐conservative processes on the observed distribution. This analysis demonstrated that the shallow hydrothermal sources present along the Tonga‐Kermadec arc are responsible for the high concentrations observed in the photic layer. Nevertheless, in contrast to what has been observed for deep hydrothermal plumes, our results highlighted the rapid decrease in DFe concentrations near shallow hydrothermal sources. This is likely due to a shorter residence time of surface water masses combined with several biogeochemical processes at play (precipitation, scavenging, biological uptake, and photoreduction). This study clearly highlights the role of shallow hydrothermal sources on the DFe cycle within the Tonga‐Kermadec arc where a strong link to biological activity in surface waters can be assessed, despite the small but significant fraction of DFe ultimately stabilized. It also emphasizes the need to consider the impact of these sources for a better understanding of the global iron cycle.

Human-induced climate change and ocean acidification are global environmental phenomena with a common driver: anthropogenic emissions of carbon dioxide. Both processes potentially threaten the Mediterranean bivalve mollusc aquaculture sector, which is economically relevant to several regions and countries. Detrimental effects on bivalve mollusc species might arise from the associated increase in sea surface temperature, pH reduction, higher frequency of extreme climatic events, and possible synergies with other nonclimatic stressors, such as harmful algal blooms and mollusc diseases. This paper presents the results of a questionnaire-based study of Mediterranean bivalve mollusc producers from 12 coastal regions and six countries, the latter including those with the highest production share in the Mediterranean region. This study aims to assess knowledge and perception of threat of climatic and nonclimatic environmental stressors within the Mediterranean aquaculture industry. Furthermore, it collects information about the (geographical) impacts of summer heat waves and ocean acidification. The results suggest that ocean acidification is still a relatively unknown phenomenon and generally poorly understood.Moreover, it is considered a secondary threat compared with other pressures. Summer heat waves are presently perceived as the highest threat, having been observed in amajority of the studied production sites in past years,with effects on seed (spat), adultmortality, and byssus attachment.

11 pages, 6 figures Mediterranean Sea fisheries supply significant local and international markets, based largely on small pelagic fish, artisanal fisheries and aquaculture of finfish (mainly seabass and seabream) and shellfish (mussels and oysters). Fisheries and aquaculture contribute to the economy of countries bordering this sea and provide food and employment to coastal communities employing ca 600,000 people. Increasing temperatures and heat wave frequency are causing stress and mortality in marine organisms and ocean acidification is expected to worsen these effects, especially for bivalves and coralligenous systems. Recruitment and seed production present possible bottlenecks for shellfish aquaculture in the future since early life stages are vulnerable to acidification and warming. Although adult finfish seem able to withstand the projected increases in seawater CO, degradation of seabed habitats and increases in harmful blooms of algae and jellyfish might adversely affect fish stocks. Ocean acidification should therefore be factored into fisheries and aquaculture management plans. Rising CO levels are expected to reduce coastal biodiversity, altering ecosystem functioning and possibly impacting tourism being the Mediterranean the world's most visited region. We recommend that ocean acidification is monitored in key areas of the Mediterranean Sea, with regular assessments of the likely socio-economic impacts to build adaptive strategies for the Mediterranean countries concerned This study was conducted as part of the Centre Scientifique de Monaco research program, funded by the Government of the Principality of Monaco Peer Reviewed

Arctic marine ecosystems are experiencing rapid environmental change with respect to warming. This is leading to an increased frequency, duration, and intensity of marine heatwaves. The impact of these stochastic heatwave events have the potential to negatively effect temperature-sensitive, habitat forming, kelp, that exist in the lower Arctic region. We tested the potential impacts of two heatwave events on mixed kelp communities occurring in the lower Arctic by conducting a 1-month ex situ mesocosm experiment in Tromsø, Norway. Each mesocosm was stocked with ~ 2.5 kg fw (fresh weight) of kelp, 200 g fw of snails and mussels, and ~ 750 g of sea urchins. Three experimental conditions were tested: a constant high temperature which was + 1.76°C above a dynamic control, and two heatwave scenarios. Scenario 1 was a long duration at + 2.8°C above the control for 2 weeks, and scenario 2 was a high frequency and magnitude treatment with conditions + 3.8°C above the control. This occurred at two peaks that were one weak apart and returned to + 1.76°C in-between. Three-hour incubations were performed to examine net community productivity (NCP) for the mixed kelp communities. We identified that both heatwave scenarios diminished the total gross production over the experimental period compared to the control and between scenario 1 and scenario 2. Scenario 1 appeared to exhibit the lowest total gross community production over the experimental period.

Further descriptions:* Treatment is the assigned condition: C0, C1, C2, C3 with M0 - M2 as replicates * ID is the tag number assigned to every individual kelp

Arctic marine ecosystems are experiencing rapid environmental changes with respect to warming, ice melt, and terrestrial run-off. The effects of these perturbations can act as multi-stressors where warming sea seawater, in combination with freshening from ice melt, and increased turbidity from terrestrial run-off affect benthic community structure and function. To examine the effects of warming, freshening, and turbidity on habitat forming macroalgae, we conducted a 2-month long ex situ experiment on mixed Arctic kelp communities in Ny-Ålesund, Svalbard from 03/07/2021 - 26/08/2021. Three experimental conditions (with 3x replicates) were tested against a dynamic real-time control where temperature was increased by + 3.3 and + 5.3 °C, salinity was reduced by ~ 4 and ~ 5, and irradiance was statically attenuated by ~ 25 and 40 % in 2 treatments. The third treatment was only warmed by + 5.3 °C from the control. In each 1 m³ mesocosm, oxygen (% O2), temperature, salinity, and photosynthetically active radiation (PAR) were continuously monitored. Mixed kelp communities comprised a biomass of ~ 4 kg fw (fresh weight) and ~ 500 g fw of small fauna. Weekly incubations were performed to calculate net community productivity (NCP) and used to estimate kelp benthic metabolism. We determined non-significant differences across treatments and provide NCP rates for mixed kelp communities in the Arctic.