Climate change is causing a worldwide decline in biodiversity, but it is also altering energy flow between trophic levels in both brackish waters and the subarctic region. In Lapland, changes in the biomass of small herbivores are rapidly reflected in the reproductive success of the larger animals that feed on them. A recently published longitudinal study conducted at the northernmost region of Finland shows how the biomass of moths, which are a vital food source to insectivorous birds, has changed over the past few decades.

Regime shifts in the Atlantic Ocean, which have subsequently affected the Baltic Sea, are also impacting moths in Lapland, according to a new study conducted at the University of Turku in Finland.

Researchers investigated how the populations of various moth species have fluctuated between 1972 and 2017, and which climate variables are linked to moth populations. The study was conducted at the Kevo Research Station located at Utsjoki in the northernmost part of Finland. The results show that the total moth biomass had moderately increased at Kevo in the past 45 years.

“In our study, we discovered that total moth biomass and biomass of different moth groups are clearly connected to the regime shifts in the Atlantic Ocean and the Baltic Sea,” says Postdoctoral Researcher Julia Fält-Nardmann from the University of Turku.

Regime shifts are changes in marine ecosystems where they shift from one stable state to another, for example, due to abrupt changes in salinity or temperature.

“Two regime shifts occurred during the four decades covered by our monitoring data. The same large-scale climate systems linked to the Atlantic Ocean regulate both the marine environment of the Baltic Sea and the terrestrial ecosystems of Lapland,” describes Principal Investigator Jari Hänninen from the University of Turku.

In addition, individual moth groups were affected by the minimum and maximum temperatures of different seasons and degree-day variables of the entire year.

“Local weather variables impact moths, for example, through the timing of budburst of their host plants and through overwintering conditions—larvae that overwinter in the ground, for instance, may suffer from repeated freezing and thawing of the soil,” Fält-Nardmann explains.

Different impacts of climate change are reflected on moths in Lapland

In Finland, the monitoring of moth populations using light traps has been a long-standing practice. The northernmost light traps were set up at the beginning of the 1970s at the Kevo Research Station of the University of Turku in Utsjoki, Lapland. These kinds of long-term monitoring data have now become an extremely valuable source of information for studying the impact of climate change on different living organisms.

Moths, and especially their larvae, play a key role in the fragile subarctic ecosystems. Many species exhibit cyclical patterns, meaning that during peak years their numbers can be thousands of times greater than during the periods between mass outbreaks. For mountain vegetation, this means widespread defoliation recurring roughly every ten years, while for insectivores, it means significant variations in food availability across different years and generations.

The results of the recently published study, which show an increase in the total moth biomass, clearly differ from the alarming global trends of declining insect populations. However, the total biomass is only part of the overall picture. In Lapland, as elsewhere in the world, insect populations that specialise in certain host plants have declined. At the same time, species that feed on a variety of host plants have become more common. Similarly, moths that overwinter as eggs, for example, fare better in a warming climate than species that overwinter as larvae.

The remote location of the Kevo Research Station can also partly explain the results.

“Elsewhere, the negative impact of human activities can obscure the results of corresponding studies. Kevo is far away from cultivated land and urban areas, which makes it an ideal place to study the impact of climate
change on organisms,” Fält-Nardmann highlights.

“Furthermore, the climate in polar regions has warmed much faster compared to other parts of the world.”

The research group from the University of Turku led by Jari Hänninen have earlier published a study where the same regime shifts were found to have an impact on the biomass of zooplankton in the Baltic Sea. However, unlike that of the moths, the biomass of these tiny marine arthropods has declined, which in turn affects the fish populations that eat them, such as the Baltic herring.