Life as we know it is based on the balance of energy and essential nutrients. Omega-3 and omega-6 polyunsaturated fatty acids (PUFA), found in insects and arachnids, play an important role in this balance.
These organisms are essential for birds, hedgehogs, and lizards, although the benefits depend largely on the type of insects and spiders consumed.
Insects with fatty acids
By now, you are probably surprised that aquatic insects like dragonflies or caddisflies contain higher concentrations of long-chain omega-3 PUFA as compared to their terrestrial equivalents.
This is a good example of fatty acids bioaccumulating through food chains. For example, whatever anybody eats, algae are on the bottom of aquatic food chains, eaten up by mayflies, which in turn are eaten by fish.
Mayflies are known to contain greater fatty acid content than the algae they consume; however, mayflies being consumed by fish do possess much more.
There is a wealth of research on this topic, in addition to exploring how plant or algae biodiversity affects biomass in ecosystems.
Biodiversity, Insects and Fatty Acids
Cornelia Twining is the director of the Institute for Food Web Ecophysiology at the Eawag Institute for Aquatic Studies and a professor at ETH Zurich.
“Unfortunately, knowledge about how insect and arachnid biodiversity can affect fatty acid availability in a food web is rather sparse,” Twining said. She, along with her colleagues, is working hard to fill this knowledge gap.
Land use and nutrient availability
Based on data from over half a million observations of approximately 7,600 insect and spider species across Switzerland, the research covered four hundred aquatic ecosystems and three hundred terrestrial ecosystems.
These ecosystems vary in terms of land use, from natural habitats such as meadows and forests to sites in city centers and agricultural areas.
“We have been interested in how land use determines the availability of energy and nutrients and whether or not there are key differences between aquatic and terrestrial ecosystems,” said Ryan Shipley, a researcher at the WSL Institute for Snow and Avalanche Research (SLF) and lead author of the study.
“Land use change is among the most pressing global issues, so understanding how human activities affect fundamental ecosystem characteristics is critical.”
Fatty acid content in insects
The data analysis showed that in the communities studied, a decrease in insect and spider biodiversity led to a decrease in biomass and content of key fatty acids.
“In terrestrial communities, we also see considerable variations depending on land use,” Twining said. Even if biodiversity is the same, insect and spider communities in an urban park typically offer less omega-3 LC-PUFA than those in a forested area.
“This is partly due to the unique species composition of these populations, and partly because biomass is lower in urban areas – there are also fewer predators such as spiders or giant beetles, which accumulate LC-PUFA on terrestrial structures,” Twining explained.
Land use and aquatic ecosystems
What surprised the scientists was that the impact of land use is much less reported in aquatic communities.
On land, the differences are more marked if predators such as spiders, which take up large amounts of important fatty acids, are removed from the atmosphere, the impact is wide-ranging. “However, this does not mean that the range of aquatic insects is not equally important,” Twining emphasizes.
Aquatic organisms are essential sources of fatty acids for terrestrial food webs. In urban regions, where insect and spider loss is high due to increasing pressure from human land use, aquatic insects become an excellent, critical additional source of vital fatty acids for birds, bats, or lizards.
But these essential “superfoods” are regularly contaminated by pollutants in streams, rivers, and lakes.
Importance of defensive biodiversity
“Our study suggests how important it is to protect biodiversity, especially in agricultural and urban regions, and to improve water to maintain food webs for ecosystem functioning,” Twining said.
The study contributes to the Blue-Green Biodiversity Research Initiative, an Eawag-WSL collaboration that focuses on biodiversity.