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Marine viruses and their role in marine ecosystems and carbon cycling
No full textMarine viral ecology emerged as a distinct discipline approximately 25 years ago. Despite significant progress, direct assessments of viral impacts on carbon flux remain scarce. Here, we integrate recent advances and knowledge gaps in marine viral ecology and a comprehensive conceptual viral-engine framework, highlighting the various ways in which viruses play a fundamental role in shaping marine ecosystem dynamics. Moreover, we present a meta-analysis of virus-mediated microbial mortality rates to examine the role of viruses in driving seasonal and global patterns in microbial biomass. We illustrate how viruses fundamentally shape marine ecosystem dynamics and serve as key drivers of microbial turnover, nutrient recycling, and global carbon cycling, positioning them as an engine driving oceanic biogeochemical processes.</span
Identifying a sustainable operating window for seaweed aquaculture in the Global North: balancing expansion barriers and carrying capacity
No full textSeaweed aquaculture is a growing blue sector that provides many benefits to society (e.g. biomass provision for food, feed and cosmetics) and the environment (e.g. eutrophication mitigation, carbon uptake and habitat provision). Successful and sustainable production expansion requires that these activities are operated within limits of acceptable change (LAC) i.e. align with ecological and social carrying capacity. Emerging from a three-round Delphi study, this work presents, from a Global North perspective, the most relevant 1) limiting variables from the socio-environmental spheres that influence the cultivation unit (inputs), such as high operating costs or underdeveloped markets or uncertain impacts from climate change, and 2) the negative impacts of aquaculture on environment and society (outputs), such as overhyped and unrealistic expectation for seaweed cultivation, conflicts with fisheries or pollution. Consolidated lists of these inputs and outputs are accompanied by specific thresholds beyond which unacceptable changes are likely to occur. These results are placed into a globally applicable holistic framework for a multidimensional assessment of seaweed aquaculture including barriers and carrying capacity, which has been outlined for the first time for seaweed cultivation. Our results emphasize the need to include socio-economic aspects into ecosystem approaches, like profitability or social license to operate – and the need for broad stakeholder participation. This study provides thus a directly useable lists of aspects to consider for cultivators and decision-makers. And as is as such a crucial contribution for the ongoing discourse on sustainable growth of this emerging blue sector.</span
Community guidelines to increase the reusability of marine microfossil assemblage data
No full textData on marine microfossil assemblage composition have multiple applications. Initially, they were primarily used for (chrono)stratigraphy and palaeoecology, but these data are now also widely used to study evolutionary and ecological processes, such as past biodiversity and its links with environmental dynamics, or to provide a basis for conservation efforts and biomonitoring. The large range of potential applications renders microfossil abundance data ideal for reuse. However, the complexity inherent in taxonomic data, which encompass extant and extinct species, coupled with the inherent intricacies of information on biological communities extracted from sedimentary archives, poses considerable hurdles in reusing marine microfossil data, even when they are publicly available. Here, we present guidelines derived from an online survey conducted within the marine micropalaeontological community, aimed at improving the reusability of microfossil assemblage data. These guidelines advocate for clarity and transparency in the documentation of the methods and the outcome, and we outline the data attributes required for effective reuse of micropalaeontological data. These guidelines are intended for researchers who generate microfossil abundance datasets and for reviewers, editors, and data curators at repositories.A total of 113 researchers evaluated the relevance of about 50 data attributes that might be needed to enable and maximise the reuse of marine microfossil abundance datasets. Each property is ranked based on the survey results. All information is, in principle, considered “desired”. Information that improves the reusability is ranked as “recommended”, and information that is required for reuse is ranked as “essential”. Analysis of a selection of datasets available online reveals a rather large gap between data properties deemed essential by survey participants and what is actually contained in publicly available microfossil assemblage datasets. While the survey indicates that the micropalaeontological community values good data stewardship, improving data reusability still requires new efforts to incorporate all the essential information. The guidelines presented here are intended as a step in that direction. Determining the optimal forms and formats for data sharing are obvious next steps the community needs to take
Diet of breeding Caspian Terns<i> Hydroprogne caspia</i> at Banc d\u27Arguin, Mauritania, is diverse and differs between an offshore and an inshore site
No full textStudying the breeding patterns and diet of conspicuous predators is a useful way to understand the structure of marine coastal food webs. The Banc d’Arguin, Mauritania, hosts a significant portion of the West African population of a widespread and conspicuous fish predator, the Caspian Tern Hydroprogne caspia. At two small islands, the relatively offshore Arel and the inshore Zira, in the Parc National du Banc d’Arguin, the size of the colonies and the timing of the first wave of breeding were measured during the breeding seasons 2015–2018. At Arel, the summed number of nests counted varied between 128 in 2015 to 306 in 2018 and at Zira between 375 in 2015 to 279 in 2018. Breeding at Arel commenced about a month later than at Zira. During the breeding season of 2016, the diet of Caspian Terns was assessed by the identification of hard items found in pellets collected near nests. All of these appeared to be parts of fish (e.g., otoliths, bones, vertebrae, scales, bullae and atlas). Despite the effort, for Arel 47% and for Zira 45% of the fish parts remained unidentified. Nevertheless, diet composition differed in interesting ways between the two colonies. At offshore Arel, the identifiable part of the diet consisted primarily of pelagic species, namely Hemiramphidae, while at inshore Zira, pellets consisted primarily of bentho-pelagic prey, namely Cichlids. Repeated sampling across years may show whether the evidence for earlier inshore breeding holds up and is consistently correlated with dietary differences.</span
Shallow water habitats provide high-quality foraging environments for the Spoon-billed Sandpiper at a critical staging site
No full textAbundant food supply is crucial for the survival of long-distance migratory birds. The continued population decline of the Spoon-billed Sandpiper (Calidris pygmeae), a critically endangered shorebird, is primarily attributed to habitat loss and degradation. However, significant gaps remain in research on their diet and foraging habitat selection, limiting effective conservation and restoration efforts. In this study, we investigated the composition of macrobenthic communities, analyzing habitat and prey selection at the main foraging area of SBS in Tiaozini, Jiangsu Province of eastern China—their most critical staging site during southward migration. Our findings revealed 25 species of macrobenthos in foraging areas, with mobile epibenthos comprising the largest group by biomass, accounting for 73%, and having higher density and biomass nearshore. Observations of foraging Spoon-billed Sandpiper individuals indicated that shallow water habitats were their preferred foraging environments, where mobile epibenthos, which thrive in these habitats after the tide recedes, made up 81% of their biomass intake. We propose that shallow water habitats in intertidal mudflats serve as essential refuges for mobile epibenthos after tidal retreat, thereby providing Spoon-billed Sandpipers with access to high-quality food resources. Habitat protection efforts should prioritize habitats harboring extensive microhabitats with shallow water, especially the nearshore area, and further research is needed to explore the mechanisms underlying the formation of these microhabitats, with the ultimate goal of restoring more high-quality habitats for the Spoon-billed Sandpiper.</span
Precession-driven variations in phosphorus cycling facilitated Earth’s oxygenation in the early Proterozoic
No full textOxygenic photosynthesis in the ocean of the early Proterozoic may have been limited by the nutrient phosphorus. If so, precession-driven variations in riverine phosphorus input may have enhanced oxygenic photosynthesis and thereby contributed to the rise of atmospheric oxygen. Here, we combine geochemical analyses of 2.46-billion-year-old deposits of the Joffre Member of the Brockman Iron Formation (Australia) and results of a reactive transport model to reconstruct pathways of organic matter degradation and phosphorus cycling in oceanic sediments over a precession cycle. Our results support a conceptual model in which increased phosphorus availability during precession maxima at southern paleolatitudes drove net oxygen production by inducing increased reductant burial in the sediment (mainly as pyrite, vivianite and magnetite). During precession minima, legacy benthic release of methane may have enhanced photolysis of atmospheric methane, thereby allowing for additional net oxygen production. Hence, precession-driven variations in coupled carbon–phosphorus–oxygen cycling may have acted as an accelerator towards the Great Oxidation Event.</span
Benthic deposition and burial of total mercury and methylmercury estimated using thorium isotopes in the high-latitude North Atlantic
No full textThe high-latitude oceans are regions of high mercury (Hg) bioaccumulation, especially in the form of methylmercury (MeHg), which is of great concern in terms of human and ecosystem health. In the high-latitude North Atlantic (60-80°N), the deep water entrains the Hg-enriched Arctic water southwards, consequently influencing global Hg cycling. Whilst Hg removal has been proposed en route from the Arctic Ocean to the Atlantic Ocean, the factors and the mechanism underpinning this loss are poorly studied. Here, we constrained Hg behavior at the sediment–water interface during the GEOTRACES process study GApr16 in 2021 using radionuclide approaches. Excess thorium isotopes (234Thex and 228Thex) in the sediment provided evidence of significant deposition of suspended particles on top of the shallow shelves and ridges due to the flowing waters with intense nepheloid layers. The benthic deposition and burial fluxes of Hg species were then evaluated based on the 234Thex and 228Thex, respectively. This analysis showed that most of the total Hg deposited from the bottom water was buried into the sediment. The net scavenging flux was 14.8 ± 7.0 Mg y-1, explaining half of the Hg removal proposed in previous studies. In comparison, the benthic scavenging flux of MeHg was 27 ± 10 kg y-1. Due to the lower particle activity, MeHg deposited from the bottom water was not retained well in the sediment, and over half was estimated to be released again, mainly by diffusion and advection, to the water column. This efflux might account for the elevated MeHg in the overflow waters during their advection. Overall, benthic scavenging dominated the Hg loss from the water column of the high-latitude North Atlantic with the shallow shelves and ridge regions being the primary deposition zones.</span
Migration of Crab Plovers <i>Dromas ardeola</i> Wintering at Barr Al Hikman, Oman
No full textCrab plovers Dromas ardeola are shorebirds endemic to the coasts of the Indo-West Pacific biogeographical area. Very little is known about the migration of this enigmatic bird. Here, we studied the migratory itineraries of six crab plovers tracked between their wintering grounds in Barr Al Hikman, Oman, and their breeding grounds on islands in the north-west of the Arabian/Persian Gulf in Iran and Kuwait. During spring migration, all tagged birds followed a similar route. On the first leg, birds flew north over desert and mountain areas. After reaching the Arabian/Persian Gulf, they followed the northern coastline, where most birds had several stops. Birds initiated spring migratory flight between February 28 and May 7, and it took 3–24 days to travel from the non-breeding to the breeding areas. The birds spent between 96 and 174 days at the breeding colonies. Autumn migratory flights were mostly along the eastern coast of the Arabian/Persian Gulf. Four birds followed a coastal route back to Barr Al Hikman, similar to spring migration. Two birds followed a southerly route and short-cut the last stretch of 500 km by crossing the Empty Quarter (Rub Al Khali) desert region. Autumn migratory flights occurred between July 19 and October 24, lasting 3–91 days. Most migratory flights occurred predominantly between 6 p.m. and 6 a.m. and were almost always less than 25 m altitude above the Earth\u27s surface. The maximum height of 1748 m above sea level was measured above the Oman Mountains. Crab plovers were able to cross potential barriers (i.e., the two desert areas and a mountain range) within a single night. We discuss our results with respect to the migratory connectivity known for this species.</span
Corrected values of turbulence generated by general geothermal convection in deep Mediterranean waters
No full textA correction by a reduction factor O(100) is proposed for previously calculated turbulence values on unresolved convection-overturns induced by general geothermal heating in the deep Western Mediterranean. The correction includes modified application of reordering method for calculating turbulence values in convection turbulence with and without stratification above or below. The result is improved correspondence between geophysical determined heat flow through the seafloor and turbulence kinetic energy dissipation rate determined from high-resolution temperature sensors moored over 109 m in the overlying waters, with an average mixing coefficient of 0.5.</span
Flow patterns, hotspots, and connectivity of land-derived substances at the sea surface of Curaçao in the southern Caribbean
No full textThe southern Caribbean Island of Curaçao is abundant in coral reef communities, but they are declining. Land-derived nutrients and pollutants are a potential contributing factor to this decline, since these substances, after entering the ocean, can be transported towards reef sites by ocean currents. To study the movement of the substances and their potential impact on coral reefs, we developed the model SCARIBOS (South CARIBbean Ocean System), with a resolution, covering the period from April 2020 to March 2024 (excluding spin-up time) to analyse flow patterns within that period in close proximity to Curaçao. SCARIBOS is used as hydrodynamic input for Lagrangian particle tracking analysis with the Parcels framework, where we assess the distribution of positively buoyant substances and explore connectivity within Curaçao\u27s coastlines as well as with the nearby regions of Aruba, Bonaire, the Venezuelan islands, and a portion of the Venezuelan mainland. Results reveal two dominant processes: the northwest-directed Caribbean Current and weaker cyclonic eddies moving in the opposite direction. These flow patterns influence hotspot locations, with higher accumulation of positively buoyant substances occurring during eddy events. Our analysis also highlights increased particle accumulation of land-derived substances in the northwest of Curaçao, corresponding to the prevailing currents. While the focus is on land-derived nutrients and pollutants, this methodology can be extended to study other particle types such as plastic debris and coral larvae, providing valuable insights for marine conservation efforts and environmental management.</span