Report
Teaser, summary, work performed and final results
Periodic Reporting for period 1 - OTOLOG (Otoliths as metabolic loggers: Examining the physiological basis for climate resilience in wild populations of marine fish)
Teaser
Measurement of metabolic rates in the laboratory is the current approach to study the physiological ecology of fish, but this type of measurements does not capture fish performance within a complex natural environment. This major knowledge gap impedes progress in many...
Summary
Measurement of metabolic rates in the laboratory is the current approach to study the physiological ecology of fish, but this type of measurements does not capture fish performance within a complex natural environment. This major knowledge gap impedes progress in many fundamental areas of biology including fish behaviour, distribution and growth; all of which require explicit or implicit assumptions regarding the metabolic response of free-ranging individuals. In the OTOLOG project, we overcome this challenge by successfully reconstructing field metabolic rates of a teleost fish, the Atlantic cod (Gadus morhua), by using otolith carbon isotopes.
The work during the 24 months of the OTOLOG project developed a novel method to estimate the field metabolic rate (FMR) of fishes in the wild from carbon isotopic values of their otoliths. The methodology allows us to track ontogenetic variation of FMR in individual fish and assess environmental impacts on fish physiology with weekly resolution and removes a major obstacle to understanding and predicting the performance of free-ranging wild fish. The development includes (1) a lab-controlled experiment to establish a practical equation of transferring otolith metabolic proxy to oxygen consumption in Atlantic cod (Gadus morhua), (2) a validation of established otolith metabolic proxy in wild cod, and (3) an application of otolith metabolic proxy in different cod populations to answer fundamental ecological questions associated with metabolism. We achieved the aim of this project and the two main objectives:
Objective 1: Investigation of the δ13Coto proxy of fish metabolic rate in experimental fishes.
Objective 2: Exploring metabolic responses to temperature in free ranging fishes.
Work performed
The scientific importance and impact of this project is developing a novel analytical method to investigate the metabolic rate of fish in the wild performance. We delivered the general idea and potential of otolith metabolic proxy by publishing a review paper (Chung et al., 2019. Otolith δ13C values as a metabolic proxy: approaches and mechanical underpinnings. Marine and Freshwater Research, Online Early).
According to the two objectives, this project has two main outputs. The first one is successfully developing otolith metabolic proxy by a lab-controlled experiment. We transform geochemical signals to physiological parameters. The method has been published in the journal, Nature Communications Biology (Chung et al., 2019. Field metabolic rates of teleost fishes are recorded in otolith carbonate. Communications Biology 2, 24.) and reported in several scientific websites (Scientists discover natural fitness watch in fishes that records their activity levels, Science Daily. Otoliths -- the fish\'s black box -- also keeps an eye on the metabolism, EurekAlert.).
The second output is applying this method to wild cod populations. Our results reveal that the field metabolic rate of wild cod is shaped by the experienced temperature, locations, year, the types of food sources, genotypes and fishery activities. These results are in preparation for publications in the SCI journals.
Final results
The OTOLOG project provides the first high-resolution metabolic rate estimates for fish in the field. Moreover, our approach now allows researchers to make use of the large archives of otoliths systematically collected for more than 100 years in order to investigate historical and contemporary changes to fish physiology. In short, it will turn these collections into archives of fish performance.
In the OTOLOG project, we have demonstrated using otolith metabolic proxy to test ecological theory and hypotheses. In a short term, FMR response to temperature increases follows the prediction of metabolic theory. However, FMR may be altered by a long-term adaptation or continuous fishing activities. Otolith metabolic proxy provides a direct evidence to show the consequence of environmental and anthropogenic impacts on fish ecology, which cannot be detected and monitored by conventional methods. The novel method of otolith metabolic proxy would enhance the study of physiological ecology.