Midwater invertebrates in the deep ocean: Adaptations, interactions and impacts of stressors

The midwater, or deep open ocean, forms over 90% of the livable space on Earth and houses one of the largest animal communities alive. As such, midwater ecosystems form important links in oceanic food webs and play a crucial role in the regulation of our climate by keeping atmospheric carbon at depth. Yet despite their importance on a global scale, midwater ecosystems remain largely unexplored. My PhD thesis aims to investigate adaptations in midwater invertebrates, including their associations, evolution and responses to human-induced stressors. The focus was on gelatinous organisms and hyperiid amphipods, as both are highly abundant in the midwater and frequently interact. In my first chapter, I investigated the impacts of global warming and deep-sea mining induced sediment plumes on a midwater jellyfish, combining insights gained from physiology, gene expression and changes in associated microbiota. For my second chapter, I studied the interactions of hyperiid amphipods with gelatinous organisms to show how symbiotic behavior drives morphological adaptations in camouflage and eye complexity, using nearly 30 years of remotely operated vehicle observations. For my third chapter, I investigated the compound eyes in a family of closely related hyperiid amphipods (Oxycephalidae) using micro-computed tomography (micro-CT) to map their optics and model their vision. Here, I was able to show how fine-scale visual adaptations can elucidate visual ecology and provide insights into the evolutionary drivers of vision in midwater amphipods. All in all, my PhD emphasizes the importance of combining multiple methods to gain detailed insights into life in the largest, but least studied habitat on Earth

Identifying a sustainable operating window for seaweed aquaculture in the Global North: balancing expansion barriers and carrying capacity

Highlights: • Holistic framework for the sustainable window of production for seaweed aquaculture. • Interdisciplinary expert identified barriers to expansion and carrying capacity. • List of barriers and impacts with indicators and suggestions for thresholds. • We highlight the importance of socio-economic aspects for aquaculture sustainability. Seaweed 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. © 2025 The Author

EnvSeis

Shaking Boundaries: Environmental seismology across disciplines and method

Variable roles of oceanic transform faults in plume dispersion along segmented mid-ocean ridges

Highlights • Three interaction modes: on-ridge, off-ridge, and on-transform–fracture zone. • Transform faults act as barrier-, bridge-, or booster-like on plume dispersion. • Roles of transforms in plume dispersion depend on plume–ridge–transform geometry. Abstract Transform faults are integral to the mid-ocean ridge system, yet their role in modulating mantle plume dispersion along segmented ridges remains poorly understood. By compiling and analyzing the tectonic characteristics of 24 global plume–ridge–transform systems, we categorize them into three types: on-ridge, off-ridge, and on-transform–fracture zone interactions. Using 3D geodynamic models, we evaluate how transform fault length, plume–transform distance, plume–ridge distance, and spreading rate influence plume behavior. Our results reveal that transform faults can play three distinct roles in plume dispersion, depending on plume positioning relative to the ridge–transform system. Barrier-like behavior occurs when transform offset increases the separation between the plume and two ridge segments and plume material needs to cross the lithospheric discontinuity boundary along the transform fault to spread, thus strongly reducing along-ridge plume dispersion (e.g., on-ridge plumes and most off-ridge plumes beneath the outside corner of a ridge segment). Bridge-like behavior arises when plumes beneath fracture zones or near ridge–transform intersections bypass these discontinuities, enabling dispersion to both ridge segments with little reduction. Booster-like behavior emerges under certain geometries, such as inside-corner plumes or plumes beneath transform centers. In these scenarios, dispersion is enhanced by shorter plume–ridge distance, avoidance of lithospheric discontinuities, and localized strengthening of along-ridge mantle flow near the transform fault induced by strike-slip motion. These findings highlight the geometric controls on plume–ridge–transform interactions and underscore the complexity of transform fault influence in plume dynamics

Earth System responses to highly ambitious mitigation scenarios : Contributions from forcing and model uncertainties

Human activities have caused strong alterations to the climate system. International political efforts have attempted to avoid further impacts by limiting global warming levels. In this sense, highly ambitious emissions mitigation scenarios are a desirable future to be aimed for. Despite a clear necessity of reaching such scenarios, uncertainty remains on potential system responses as the importance of carbon forcing decreases. This thesis shows that varying aerosols spatial implementation allows for a considerable surface temperature variability, as well as variability in individual components’, such as land carbon uptake, contributions to the warming or cooling of the system. Triggered feedbacks due to aerosols implementations can have a crucial impact in assessing ambitious mitigation scenarios. Furthermore, the thesis introduces a new framework (FROT: Framework for Radiative cOntributions to Temperature responses), to comprehensively assess the temperature variability for different ambitious mitigation future scenarios, and to account for individual contributions from different climate components. The findings corroborate the need for including forcings and transient responses when assessing climate development. Finally, the thesis focused on techniques to remove carbon dioxide from the atmosphere. It finds that for centennial timescales dissolved ocean oxygen under cabon dioxide removal is unable to return to pre-industrial levels. This response is dependent on the region and depth considered. The findings indicate that apparent oxygen use dominates the simulated oxygen development, especially due to changes in circulation and ventilation. These findings widen the understanding of expected responses and components development under ambitious mitigation scenarios, either by reducing or by clarifying different uncertainties expected in the assessment, analysis and potential real-world outcomes of these scenarios

Seamounts of Cabo Verde: A review of their ecological and economic significance, anthropogenic impacts, and conservation needs

Highlights • Seamounts around Cabo Verde are severely understudied in all aspects of their marine ecosystem. • Faunal communities (benthic, pelagic, mobile megafauna) are abundant and diverse, with potential for endemism. • Cabo Verde seamounts deliver extensive ecosystem services, particularly food provision through fisheries. • Expected future increases in anthropogenic impacts necessitate urgent development of a conservation plan. • Effective conservation will need dialogue, strong laws, and resources for enforcement, management, and monitoring. Abstract The deep-sea areas of the Cabo Verde Archipelago remain largely unexplored, with seamounts standing out as the most prominent and abundant geomorphological features. The ecological significance of these underwater structures is well-documented in various regions of the planet, as they often serve as biodiversity hotspots, stepping stones for species connectivity and, in some cases, areas with high levels of endemism. However, the biology and ecology of the seamounts around Cabo Verde are still largely unknown. Preliminary studies of the geomorphology, oceanographic characteristics and ecology of specific features suggest that the Cabo Verde seamount network — comprising 14 known conspicuous seamounts as well as smaller elevations less than 1000 m — harbours high biological diversity. That biodiversity associated with the Cabo Verde seamounts spans a wide range of forms, from microscopic organisms to cetaceans, encompassing both pelagic and benthic communities. Commercial activities associated with seamounts, in particular fishing, are a critical aspect to consider for ecosystem management. Evaluating their current uses, future prospects, and the existing and potential threats the Cabo Verde seamounts face is essential for effective and sustainable marine spatial planning. This study reviews and synthesises the current knowledge on the Cabo Verde seamounts within its Exclusive Economic Zone (EEZ), focusing on their environmental and biological aspects, including geology, oceanography, and associated biological communities. Key topics include primary production, zooplankton communities, benthic organisms, large vertebrates such as elasmobranchs, sea turtles, seabirds, and cetaceans, as well as microbes and trophic linkages. Additionally, this review explores the socio-economic dimensions linked to seamounts, highlighting their importance to the local economy and emphasizing the need for effective marine spatial management plans. These considerations are crucial for balancing conservation efforts with sustainable use, ensuring the long-term health of these vital underwater ecosystems

Trace elements in rivers draining tropical peat swamp forests

Tropical peat swamp forests are wetland ecosystems characterized by peat accumulation from partially decomposing organic matter in lowland areas. In southeast Asia, tropical peat swamps account for about 11-14% of the carbon stored in all peatlands. However, converting these ecosystems for agricultural activities has potential implications for releasing materials, including trace elements. This study explores the interplay of anthropogenic activities and trace element export to the estuaries and coastal waters. The result indicated the role of pH, salinity, dissolved organic carbon (DOC), and iron (Fe) and manganese (Mn) oxides in regulating the global biogeochemical cycling of trace elements. Seasonal variabilities contribute to trace element fluxes, especially during the wet season (December), with implications for material supplies to the coastal waters. The NICA- Donnan model was used to investigate the combined impact of DOC and pH on the formation of solid iron hydroxide (Fe(OH)3(s)). The Maludam River was predicted to be supersaturated for Fe hydroxides, and the field results affirmed our model prediction. The output showed Fe and Cu had a strong affinity for DOC and, to a lesser extent, Al and Ni in the conditions prevailing at the study sites. Furthermore, the concentration of DOC (12000 μmol L−1) in the natural peat increased, while the concentration of trace elements increased in the disturbed peat. Porewater samples from the disturbed and natural peat also indicated enhanced trace element concentrations in the disturbed peat compared to the natural peat. The observed increase in trace element concentrations reflects the impact of peat conversion on agricultural activities and catchment chemistry

Eddy Hunter: A Data Mining System for High-Resolution Eddy Signals, Leveraging Spatio-Temporal Similarities in the SWOT Satellite Data

The SWOT mission opened a new chapter in understanding ocean dynamics, yielding constantly growing amounts of high-resolution Sea Surface Height (SSH) observations. However, this extremely valuable data source is still not fully exploited by researchers, due to technical reasons and novelty. In particular, long orbit cycles and KaRIn altimeter’s limited spatial coverage impose challenges for eddy detection and tracking using SWOT. Conversely, traditional satellite altimeters served as the backbone of mesoscale research for over 30 years, providing wide spatio-temporal coverage. The integration of such satellites and SWOT could offer possible solutions to some of the aforementioned challenges. We aim to provide a system capable of overcoming the limitations of KaRIn altimetry data, leveraging the integration between SWOT and conventional SSH altimetry. Adopting an information retrieval approach, we identify and index high-resolution eddy signals similar to a low-resolution counterpart. To do so, the Eddy Hunter System (EHS) integrates the Mesoscale Eddy Trajectory Atlas (META) and SWOT Level-3 products, by leveraging the spatio-temporal similarities in the SSH signals. The EHS extracts a spatio-temporal Region Of Interest (ROI) from every eddy observation present in the META and computes the SWOT passages that could possibly contain related signals. The introduction of “Marine Data Science” topics in the similarity-search community can provide new problems and challenges regarding information retrieval and data mining. The deployment of our system could foster advancements both in oceanographic and applied ML/AI research, providing a powerful data mining tool to build high-resolution eddy repositories and unveil previously unseen ocean phenomena