Climate change is reducing the size and survival of aquatic insects, according to a study.

Seville, July 10 (EFE).- An international study led by the Doñana Biological Station-CSIC has revealed that the reduced availability of oxygen in warm waters due to high temperatures associated with climate change reduces the size of aquatic insects, compromising their survival.

According to a report by the Spanish National Research Council (CSIC) on Thursday, this situation increases the risk of deterioration of aquatic ecosystems, which would translate into a reduced availability of fish due to significant impacts on the food web.

The global rise in temperatures is leading to greater warming of marine and continental waters, with effects such as a decrease in oxygen solubility.

This lower concentration of oxygen in the water affects fish, aquatic insects, and microorganisms that need it to breathe.

"The decline in size is another aspect of the general decline in insects, associated with rising temperatures. Not only are there fewer insects, but they may also be smaller," said Viktor Baranov, a researcher at the Doñana Biological Station and first author of the study. This dual effect on the size and number of aquatic insects would be reducing their capacity to maintain crucial ecosystem functions.

Experiment on temperature, oxygen and size

To conduct this study, the team designed an experiment to evaluate the relationships between water temperature, oxygen concentration, and the size of a species of fly of the genus Chironomidae (Chironomus riparius), whose larvae are aquatic.

The size and survival of the insects were compared in six different scenarios: three at a temperature of 20 degrees, with high, medium, and low oxygen concentrations, and another three at 30 degrees, with the same three oxygen concentration levels.

The results were robust and echo those obtained in another study published in 2021, in which Baranov also participated, which found that the size of flies of this genus and temperature were related.

The commonly known as non-biting midges or 'chironomid' midges are so named because of their resemblance to common mosquitoes (Culicidae), but they have important differences, especially the fact that they do not bite or feed on blood.

Its genome has been sequenced and is used as a model to assess environmental stress and the impact of pollutants on aquatic ecosystems.

In the new study, larvae that developed in warm waters with low oxygen concentrations were 10% smaller than those that developed in the other five scenarios. These conditions also caused faster growth and higher mortality in the insects.

Growth problems

"Since climate change is causing temperatures to rise, and oxygen is less soluble in warmer waters, the larvae of these animals are having trouble growing. This is because respiration is essentially a driver of animal growth," the researcher explained.

Aquatic insects are essential for the purification of aquatic pollution and the assessment of water quality, as well as for the proper functioning of the food web, since they are food for many other species.

As adults, these insects also perform other functions, such as crop pollination, and some also have recreational functions for humans, as is the case with dragonflies, which have an important aesthetic and cultural component.

"Due to their prominent role, the negative effects of climate change on these organisms are extremely significant," Baranov emphasized.

The work is a starting point for a broader study of the effects of climate change on animal functional traits, such as size, and is in addition to the widely documented decline in insect numbers.

It also opens the door to research into how the decline in animal size affects the ecosystems they comprise.

This study, published in the journal Ecological Entomology, was carried out in collaboration with the Slovak Academy of Sciences and the University of Granada. EFE