MudNut: Mudflat foraminifera as potential nutrient filters towards the shelf – A biogeochemical perspective

• Applicant: Dr. Nicolaas Glock
• Subject Area: Palaeontology ; Geology
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 572775769

Intertidal mudflats are highly productive habitats and an important sink for atmospheric CO2. Some species of benthic foraminifera thrive in these environments. They have diverse survival strategies to cope with the strong environmental gradients that can occur in mudflat sediments, such as variations in salinity and the oxygen penetration depth. Recently, it has been discovered that benthic foraminifera store large quantities of phosphate intracellularly. This intracellular phosphate storage most likely enables them to remain mobile during oxygen depletion and adjust their intracellular electrolyte concentrations in response to changes in osmotic pressure. Phosphate is an important macronutrient, which is widely used as fertilizer and can leak into the ocean. The phenomenon of intracellular phosphate storage is widespread among foraminifera, from intertidal mudflats to the deep sea and most likely buffers coastal eutrophication. The highest intracellular phosphate concentration has been found in the species Ammonia confertitesta. This species is abundant and invasive in European mudflats and is likely to influence the nutrient dynamics in these environments, due to its presence. The aim of this project is to monitor the seasonal population dynamics and intracellular phosphate concentrations of benthic foraminifera in the tidal mudflats of Friedrichskoog and Meldorf in the Wadden Sea, Germany. These results will be compared with oxygen and phosphate gradients within the pore water, as well as with the dynamics of different phosphorus phases in the sediments (e.g., phosphorus bound to iron oxyhydroxides, authigenic apatite, etc.). The resulting data will provide a thorough overview of the seasonal variability in the amount of phosphate, stored in foraminifera in this environment, compared to the total sedimentary phosphate fluxes, and will provide insight into whether mudflats can act as a 'nutrient filter' towards the shelf. Additionally, I intend to further characterize the phosphorus compounds in foraminifera. Intracellular phosphorus compounds will be extracted by cell lysis and analysed using nuclear magnetic resonance (NMR) spectrometry at Hamburg University and Orbitrap mass spectrometry (Orbitrap MS) at JAMSTEC in Japan. Furthermore, cryo-scanning electron microscopy coupled with energy dispersive X-ray spectrometry (cryo-SEM/EDS) will be employed to localize the intracellular phosphate storage within A. confertitesta. This will improve our understanding of the biological functions of A. confertitesta’s particular high intracellular phosphate concentrations of and whether this storage provides this invasive species with an advantage over endemic species in this environment. Additionally, empty (“dead”) foraminiferal tests will be analyzed using SEM/EDX to screen for potential apatite phases or precursors in the tests that might have been nucleated post-mortem by the high intracellular phosphate concentration of the foraminifera.

• DFG Programme: Research Grants
• International Connection: Japan
• Co-Investigator: Professor Dr. Gerhard Schmiedl
• Cooperation Partner: Dr. Hidetaka Nomaki