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

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

On the importance of Mongolian cyclones to East Asian dust storms

In East Asia, dust storms typically occur in spring with adverse impacts on socio-economic activities, loss of life, and climate. Mongolian cyclones that form downstream of the Altai-Sayan Mountain have been known for some time as drivers of spring dust storms in East Asia. The passage of Mongolian cyclones primarily induces dust-emitting winds in the Gobi Desert, leading to dust emissions and favoring the subsequent transport of dust aerosols across Northern China. Herein, the relative contributions of Mongolian cyclones to dust emissions in the Gobi Desert and subsequent dust storm activity in Northern China are assessed from a climatological perspective for the first time in this dissertation. Furthermore, this study provides the first evidence that dust activity in the Taklamakan Desert, which is located in the west of the Gobi Desert, is also supported by Mongolian cyclones. This assessment aims to illustrate the importance of Mongolian cyclones in generating spring dust storms across East Asia

High trophic plasticity in the mixotrophic Mastigias papua-Symbiodiniaceae holobiont: implications for the ecology of zooxanthellate jellyfishes

The trophic ecology of mixotrophic, zooxanthellate jellyfishes potentially spans a wide spectrum between autotrophy and heterotrophy. However, their degree of trophic plasticity along this spectrum is not well known. To better characterize their trophic ecology, we sampled the zooxanthellate medusa Mastigias papua in contrasting environments and sizes in Palau (Micronesia). We characterized their trophic ecology using isotopic (bulk δ13C and δ15N), elemental (C:N ratios), and fatty acid compositions. The different trophic indicators were correlated or anti-correlated as expected (Pearson’s correlation coefficient, rP > 0.5 or < -0.5 in 91.1% of cases, p < 0.05), indicating good agreement. The sampled M. papua were ordered in a trophic spectrum between autotrophy and heterotrophy (supported by decreasing δ13C, C:N, proportion of neutral lipid fatty acids (NLFA:TLFA), n-3:n-6 and increasing δ15N, eicosapentaenoic acid to docosahexaenoic acid ratio (EPA:DHA)). This trophic spectrum was mostly driven by sampling location with little influence of medusa size. Moreover, previous observations have shown that in a given location, the trophic ecology of M. papua can change over time. Thus, the positions on the trophic spectrum of the populations sampled here are not fixed, suggesting high trophic plasticity in M. papua. The heterotrophic end of the trophic spectrum was occupied by non-symbiotic M. papua, whereas the literature indicates that the autotrophic end of the spectrum corresponds to dominant autotrophy, where more than 100% of the carbon requirement is obtained by photosynthesis. Such high trophic plasticity has critical implications for the trophic ecology and blooming ability of zooxanthellate jellyfishe

Ecology of Moroteuthopsis longimana at the sub-Antarctic Prince Edward Islands, revealed through stable isotope analysis of squid beaks

Understanding the underlying ecological factors that affect the distribution patterns of organisms is vital for their conservation. Cephalopods such as giant warty squids Moroteuthopsis longimana are important in the diets of marine predators, including grey-headed albatrosses Thalassarche chrysostoma, yet our understanding of their habitat and trophic ecology remains limited. We investigated the habitat and trophic niche utilised by M. longimana through the delta C-13 and delta N-15 profiles captured in their beaks. M. longimana beaks were collected around grey-headed albatross nests at the Prince Edward Islands during 2004 and 2013 (n = 40 beaks). The results showed distinctly Antarctic distributions (delta C-13 = -24.0 +/- 1.0 parts per thousand, mean +/- SD) for M. longimana, consistent with albatrosses foraging at the Southwest Indian Ridge, as opposed to broader foraging zones utilised by albatrosses from Iles Crozet and Iles Kerguelen. Slightly lower delta N-15 values (5.4 +/- 0.7 parts per thousand) were found compared to other islands in the Indian Sector of the Southern Ocean, which may indicate more crustaceans in the squid diets. Sequential sampling along the lateral walls of individual beaks (n = 4) revealed ontogenetic shifts in delta C-13 and delta N-15 values, but individual variation in these shifts requires further investigation

Moderately thermophilic nitrifying bacteria from a hot spring of the Baikal rift zone

Samples from three hot springs (Alla, Seya and Garga) located in the northeastern part of Baikal rift zone (Buryat Republic, Russia) were screened for the presence of thermophilic nitrifying bacteria. Enrichment cultures were obtained solely from the Garga spring characterized by slightly alkaline water (pH 7.9) and an outlet temperature of 75°C. The enrichment cultures of the ammonia- and nitrite oxidizers grew at temperature ranges of 27–55 and 40–60°C, respectively. The temperature optimum was approximately 50°C for both groups and thus they can be designated as moderate thermophiles. Ammonia oxidizers were identified with classical and immunological techniques. Representatives of the genus Nitrosomonas and Nitrosospira-like bacteria with characteristic vibroid morphology were detected. The latter were characterized by an enlarged periplasmic space, which has not been previously observed in ammonia oxidizers. Electron microscopy, denaturing gradient gel electrophoresis analyses and partial 16S rRNA gene sequencing provided evidence that the nitrite oxidizers were members of the genus Nitrospira

New species in Galeommatoidea (Bivalvia) from Namibia

Four new species in the superfamily Galeommatoidea (Bivalvia) were found in sediment samples from the continental shelf and upper bathyal slope off Namibia, SW Africa: Kurtiella namibiensis n. sp., Bornia walvisensis n. sp., Scacchia aartseni n. sp. and Scacchia huberi n. sp. One live specimen of Bornia walvisensis n. sp. was brooding. A commensal relationship is likely between Bornia walvisensis n. sp. and the decapod host Kraussillichirus kraussi (Stebbing, 1900)

Neodymium and Hafnium Isotope and Rare Earth Element Geochemical Cycling and Fluxes from the Amazon to the tropical western Atlantic

Continental margins are a dynamic interface linking the terrestrial lithosphere and oceanic hydrosphere, thus controlling fluxes of terrigenous materials from land to ocean. In particular, estuaries are places channeling vast amounts of minerals, nutrients, organic matter and trace elements (TEs) in dissolved and particulate forms into the oceans. As many TEs are essential nutrients for phytoplankton growth, their concentrations ([TEs]) together with macronutrients in surface waters influence marine primary productivity, thereby impacting ocean ecosystems and carbon cycling. However, before entering the oceans, terrigenous TEs are modified at continental margins by various processes including removal, release and recycling. Consequently, studying geochemical cycling of TEs at continental margins is crucial for discerning their sources and processes that determine TE fluxes to oceans. Radiogenic neodymium (Nd) and hafnium (Hf) isotopic compositions, expressed as εNd and εHf, respectively are sensitive tracers of the origin and mixing of water masses and seawater-particle interactions at the continent-ocean interface. In this thesis a detailed investigation of the distributions of radiogenic Nd and Hf isotopes as well as rare earth elements and yttrium (REY) is performed across the Amazon freshwater plume, the Amazonian mangrove belt and the Amazon shelf and slope as part of the GEOTRACES GApr11 cruise. The objective is to investigate the sources and processes influencing the TE supplies, Nd and Hf isotope distributions and their fluxes to the western Atlantic Ocean