Specialists from the Institute of Industrial Ecology of the North of the Kola Scientific Center of the Russian Academy of Sciences, together with colleagues from the Zoological Institute of the Russian Academy of Sciences and the Severtsov Institute of Ecology and Evolution of the Russian Academy of Sciences, conducted an ichthyological study in Lake Imandra, the largest body of water in the Murmansk Region, and found out how climate change is changing the food competition of fish in the northern lakes.
Global climate change entails a change in the structure of ecosystems, especially in high latitudes. An increase in water temperature, a shortening of the ice age and a change in the productivity of reservoirs create new conditions for freshwater inhabitants. Cold-loving species, such as whitefish or grouse, are under threat, while more unpretentious and heat-loving species, such as perch, are expanding their range to the north. Scientists assumed that this expansion could lead to the direct displacement of native species through food competition. However, until recently, the mechanisms of this interaction in subarctic conditions remained insufficiently studied.
The authors chose Lake Imandra, the largest body of water in the Murmansk region, as the object of the study. It is an important source of water supply and a fishing facility for whitefish, grouse and smelt. To obtain the primary data, the scientists used two complementary methods: the analysis of fish stomach contents and the analysis of stable carbon and nitrogen isotopes in muscle tissues.
Isotopic analysis reflects nutrition not over the last hours, but over weeks and months, since the isotopic composition of muscle tissue is updated gradually. This compensates for the limitations of the stomach contents analysis, which captures only a short-term diet. The combination of both methods gives a complete picture.: taxonomic detail and integrated assessment of trophic relationships.
In addition, the δ13C isotopic coefficient serves as an indicator of the energy source: for example, pelagic (associated with the water column) and benthic (bottom) food chains have distinct carbon signatures. The Δ1⁵n index allows us to assess the position of an organism in the food chain: the higher the value of Δ1⁵n, the higher the level in the trophic chain.
The results of the study confirmed the existence of serious food competition between whitefish, which traditionally lives in northern latitudes, and perch, which is expanding its range to the north due to warming. An analysis of the stomach contents showed that the diet of whitefish and perch coincided by 48%. Both species occupy similar trophic positions, which corresponds to the level of predators of the first order. The data obtained help to explain the reasons for the decrease in whitefish numbers in subarctic lakes. The food plasticity of perch, combined with climate warming, creates conditions favorable for the growth of its population and increases competitive pressure on cold-loving species such as whitefish.
Other fish species have occupied other niches. For example, grouse, smelt, and burbot rely more heavily on pelagic food sources, while ruff is a specialist in feeding chironomid larvae.
The authors of the work indicate that their study mainly included adults. In their opinion, it is advisable to direct further research to the study of trophic interactions in the early stages of fish development. Competition for plankton resources can be especially intense during the juvenile period, which critically affects the survival of generations.
