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AbstractOverfishing, excess nutrient load, and invasion of Mnemiopsis leidyi acted on the Black Sea from 1960s to 1990s. Under the effect of these drivers, the ecosystem underwent several transformations that culminated in the shift from a planktonic food chain to a network with most of the energy diverted to jellyfish. The interplay between multiple stressors and the intricate web of trophic interactions make it difficult to understand which causative mechanisms linked the sources of change to the observed variations. To study such interplay, we focused on the structure of the trophic interactions and applied loop analysis to qualitatively predict the response of variables to stressors. Significant variations in biomass trends were identified with statistical analysis and considered as benchmark to validate loop analysis predictions. The results of the comparisons were used to select the most influential trophic interactions that explain the changes observed between 1960 and 1990. The models were applied to test (1) the importance of various environmental drivers and (2) the mechanisms that produced the observed changes. The results suggested that the changes observed before M. leidyi invasion were strongly influenced by the excess nutrient addition, an outcome that challenges the relevance of the trophic cascade as described in literature. The concurrent effect of overfishing, climate, and nutrient enrichment likely triggered the outburst of M. leidyi in the late 1980s. Our work shows the potential of loop analysis to grasp the causal relationships between the drivers, the structure of the interactions, and the responses of the variables.

AbstractRecreational fisheries contribute substantially to the sociocultural and economic well‐being of coastal and riparian regions worldwide, but climate change threatens their sustainability. Fishery managers require information on how climate change will impact key recreational species; however, the absence of a global assessment hinders both directed and widespread conservation efforts. In this study, we present the first global climate change vulnerability assessment of recreationally targeted fish species from marine and freshwater environments (including diadromous fishes). We use climate change projections and data on species’ physiological and ecological traits to quantify and map global climate vulnerability and analyze these patterns alongside the indices of socioeconomic value and conservation effort to determine where efforts are sufficient and where they might fall short. We found that over 20% of recreationally targeted fishes are vulnerable to climate change under a high emission scenario. Overall, marine fishes had the highest number of vulnerable species, concentrated in regions with sensitive habitat types (e.g., coral reefs). However, freshwater fishes had higher proportions of species at risk from climate change, with concentrations in northern Europe, Australia, and southern Africa. Mismatches in conservation effort and vulnerability were found within all regions and life‐history groups. A key pattern was that current conservation effort focused primarily on marine fishes of high socioeconomic value rather than on the freshwater and diadromous fishes that were predicted to be proportionately more vulnerable. While several marine regions were notably lacking in protection (e.g., Caribbean Sea, Banda Sea), only 19% of vulnerable marine species were without conservation effort. By contrast, 72% of freshwater fishes and 33% of diadromous fishes had no measures in place, despite their high vulnerability and cultural value. The spatial and taxonomic analyses presented here provide guidance for the future conservation and management of recreational fisheries as climate change progresses.

Abstract This study analyzed the potential effects of gas hydrate (GH) exploitation on the geomechanical properties of hydrate-bearing sediment (HBS) by examining the combined effects of depressurization and CO2 injection using triaxial compression tests. The stress-strain behavior of the initial CH4 HBS showed strong hardening-softening characteristics and high peak strength, whereas milder hardening-softening behavior and reduced peak strength were observed after partial (20, 40, 60, and 80%) or complete GH dissociation (100%), indicating that the mechanical behavior clearly depended on dissociation ratios and GH saturations. In response to CO2 injection in partially dissociated HBS, subsequent CH4–CO2 hydrate exchange, and secondary CO2 hydrate formation, the mechanical strength of the replaced HBS recovered significantly, and stress-strain characteristics were similar to that of the 20% dissociated CH4 HBS. Although total CH4 recovery was increased by the combination of depressurization and replacement, optimum recovery was found at a dissociation ratio of 20% followed by replacement because production by replacement decreased as the dissociation ratio increased. These results contribute to the understanding of how depressurization and CO2 injection schemes may be combined to optimize energy recovery and CO2 sequestration. In particular, this research demonstrates that CH4–CO2 hydrate exchange and secondary GH formation are suitable methods for controlling and maintaining the mechanical stability of HBSs.

The persistent massive blooms of gelatinous zooplankton recorded during recent decades may be indicative of marine ecosystem changes. In this study, we investigated the potential influence of the North Atlantic climate (NAO) variability on decadal abundance changes of gelatinous carnivore zooplankton in the Mondego estuary, Portugal, over the period 2003-2013. During the 11-year study, the community of gelatinous carnivores encompassed a larger diversity of hydromedusae than siphonophores; the former dominated by Obelia spp., Lizzia blondina, Clythia hemisphaerica, Liriope tetraphylla and Solmaris corona, while the latter dominated by Muggiaea atlantica. Gelatinous carnivore zooplankton displayed marked interannual variability and mounting species richness over the period examined. Their pattern of abundance shifted towards larger abundances ca. 2007 and significant phenological changes. The latter included a shift in the mean annual pattern (from unimodal to bimodal peak, prior and after 2007 respectively) and an earlier timing of the first annual peak concurrent with enhanced temperatures. These changes were concurrent with the climate-driven environmental variability mainly controlled by the NAO, which displayed larger variance after 2007 along with an enhanced upwelling activity. Structural equation modelling allowed depicting cascading effects derived from the NAO influence on regional climate and upwelling variability further shaping water temperature. Such cascading effect percolated the structure and dynamics of the community of gelatinous carnivore zooplankton in the Mondego estuary.