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From biogeochemistry to the ecological genomics of pelagic fish stocks - a study across 4 trophic levels

English title From biogeochemistry to the ecological genomics of pelagic fish stocks - a study across 4 trophic levels
Applicant Wehrli Bernhard
Number 166589
Funding scheme Interdisciplinary projects
Research institution Abteilung Oberflächengewässer EAWAG
Institution of higher education Swiss Federal Institute of Aquatic Science and Technology - EAWAG
Main discipline Hydrology, Limnology, Glaciology
Start/End 01.04.2016 - 31.03.2020
Approved amount 773'016.00
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All Disciplines (4)

Hydrology, Limnology, Glaciology

Keywords (6)

pelagic fish; upwelling; local adaptation; nitrogen isoptopes; nutrients; sensors

Lay Summary (German)

Der Tanganyikasee ist der zweittiefste See der Erde und liegt südlich des Äquators in Ostafrika. Im Laufe von etwa 10 Millionen Jahren Evolutionsgeschichte hat sich im See eine grosse Artenvielfalt entwickelt. Für die Proteinversorgung in der Region hat die Fischerei eine grosse Bedeutung. Die lokalen Fischer fangen vor allem Sardinen aber auch Barsche. Über die Ökologie, Evolution und genetische Vielfalt dieser Fischarten ist allerdings nur wenig bekannt. Der 670 km lange Tanganyikasee wird im Norden und Süden durch unterschiedliche Nährstoffkreisläufe geprägt. Punktmessungen und Satellitendaten zeigen eine höhere Produktivität im Süden und eine stärkere Schichtung im Norden des Sees. Daraus ergeben sich unterschiedliche Raten der Stickstofffixierung, was sich in der Isotopensignatur der Aminosäuren von Plankton und Fischen niederschlagen müsste.
Lay summary

Das Projekt basiert auf einer interdisziplinären Zusammenarbeit zwischen Spezialisten für Fischökologie und –evolution, Biogeochemie sowie den Wissenschaftlern des Tansanian Fisheries Research Institute (TAFIRI). Mit biogeochemischen Ansätzen wird das Projekt (i) die unterschiedlichen Nährstoffkreisläufe und Stickstoff Fixierungsraten entlang des Sees quantifizieren (ii) die räumlich - zeitlichen Unterschiede in der Plankton Biomasse erfassen und (iii) Isotopensignaturen entlang der Nahrungskette bis zu den Fischen bestimmen. Mit fischökologischen und molekularbiologischen Methoden wird das Projekt (iv) die räumliche Ausdehnung von Fischpopulationen und ihre genetische Struktur analysieren, (v) die unterschiedlichen Nahrungsquellen und Muster für lokale Anpassung der Fischgemeinschaften erfassen, um damit (vi) die Veränderungen der Fischpopulationen besser zu verstehen.

Unsere Mitarbeiter werden mit Partnern des TAFIRI sowie mit dem internationalen CLEAT- Konsortium zusammenarbeiten, welche sich zum Ziel gesetzt haben, das Fischereimanagement am Tanganyikasee mit wissenschaftlichen Informationen zu unterstützen.
Direct link to Lay Summary Last update: 08.04.2016

Responsible applicant and co-applicants


Associated projects

Number Title Start Funding scheme
128707 High resolution in situ nutrient mapping of large rivers and reservoir systems 01.04.2010 R'EQUIP
157750 Cluster of sondes for the high-resolution analysis of aquatic ecosystems 01.12.2014 R'EQUIP
183566 20,000 years of evolution and ecosystem dynamics in the world’s largest tropical lake reconstructed from sediment cores, fossils and ancient DNA 01.03.2019 Sinergia


Lake Tanganyika harbors the world’s second largest freshwater system by volume. Situated south of the equator, the 670 km long lake extends over 6° of latitude. The tropical climate induces a permanent stratification, which separates the nutrient-rich deep water from the productive zone. The seasonal monsoon and differential cooling drive a complex current system with longitudinal water transfer and different upwelling regimes in the north and south basins. Comparative studies reported seasonal and spatial variation in redox conditions, nutrient supply and primary productivity. At 9-12 million years in age, the lake hosts a long history of evolution with a rich diversity of endemic species. The inland fishery on Lake Tanganyika is an important protein source for the riparian population and critically depends on three pelagic fish species. Strong fluctuations in fish catches have been a focus of several recent studies. Although genetic data are essential to infer geographic scales of population structure, spatial patterns of movement between regions, and to understand the degree to which local adaptation may exist within species, genetic work on these fish is largely nonexistent. Here we propose an interdisciplinary collaboration to elucidate the different biogeochemical drivers for the pelagic food webs along latitudinal gradients, and to analyze to what extent pelagic fish populations have adapted to these habitat gradients and to seasonal fluctuations along the lake. With the planned field campaigns we will-Better characterize the basin-scale circulation and upwelling using non-reactive tracers, high-resolution sensor profiles, and biogeochemical modeling-Test available evidence for different rates of nitrogen fixation and nutrient upwelling along the north-south gradient during the dry and wet seasons by sensor-driven high-resolution sampling and analysis-Characterize spatial and seasonal differences of plankton composition based on nitrogen isotope signatures as well as continuous on-ship monitoring of algal pigments along the lake.Together with these biogeochemical studies, we propose to conduct the first comprehensive population genomics and ecological analysis of pelagic fish in Lake Tanganyika in order to analyze to what extent the main pelagic fish species are genetically and ecologically structured, and to what extent phenotypic and genomic variation reflects adaptation to the habitat gradients in this large lake. Specifically, we will:-Estimate the levels of gene flow, geographic scales of population genetic structure, and genetic effective population sizes, among pelagic fish populations based on next-generation sequencing and newly developed spatial modeling approaches for genomic data.-Link genetic data to ecological data on fish diet (stomach contents, stable isotopes), and to patterns of local adaptation using information about feeding-related morphological traits (gill rakers, head and mouth shape). -Reconstruct historical genetic effective population sizes and fluctuations in the exploited Lates species by analyzing genomic data with Bayesian coalescent-based approaches, to place current population declines in a deep historical context. In a joint effort, we propose to work across 4 trophic levels by studying 15N transfer from phytoplankton assemblages to zooplankton. At the third trophic level we will apply compound-specific 15N isotope analysis on amino acids on Stolothrissa and Limnothrissa that both feed entirely on zooplankton. At the fourth level we will study Lates stappersi that feeds on the clupeids in some parts of the lake and on shrimps in other parts. The 15N analysis will be crucial to resolve extent and location of foraging grounds of these three dominant pelagic fish species. This new approach offers a link between advanced population genetic analysis and the biogeochemical analysis of nitrogen transfer over four trophic levels from dissolved nutrients to the commercially important pelagic fish in Lake Tanganyika.