Revealing physiological stress from climate change in Baltic Sea cod using a new metabolic index based on otolith stable carbon isotope analysis

The Baltic Sea has the largest anthropogenically induced hypoxic area in the world, and climate change is rapid here. This has consequences for the physiological performance and biogeographical distribution of aquatic organisms.

To quantify the effects of changing environmental conditions on fish metabolism, I will develop a new metabolic index based on estimates of the field metabolic rate (FMR), using Baltic Sea cod (Gadus morhua) as a case study.

FMR is the sum of all energy expenses of an organism in the wild and thus a relevant ecophysiological metric gauging the impact of the environmental stress in the metabolic performance of fishes.

To determine how FMR vary over different oxygen concentrations, I will obtain otoliths (ear stones) from cod caught across different oxygen concentrations along the Swedish Baltic Sea coast.

The carbon isotope composition of otoliths will be measured and FMR calculated using a newly established relationship between the proportion of metabolic carbon in the otolith and metabolic rates.

The FMR data will then be incorporated into a new metabolic index, and related to the body condition of cod, and their spatial distribution, using advanced geostatistical models. The models will be used to project the spatial distribution of cod in future environmental conditions.

Understanding how FMR shapes the condition, productivity, and distribution of fishes is important for their conservation and sustainable management under environmental change.