Production, distribution, and abundance of long-chain omega-3 polyunsaturated fatty acids: a fundamental dichotomy between freshwater and terrestrial ecosystems

Abstract

Long-chain polyunsaturated fatty acids (LC-PUFA) are critical for the health of aquatic and terrestrial organisms; therefore, understanding the production, distribution, and abundance of these compounds is very important. Although the dynamics of LC-PUFA production and distribution in aquatic environments has been well documented, a systematic and comprehensive comparison to LC-PUFA in terrestrial environments has not been rigorously investigated. Here we use a data synthesis approach to compare and contrast fatty acid profiles of 369 aquatic and terrestrial organisms. Habitat and trophic level were interacting factors that determined the proportion of individual omega-3 (n-3) or omega-6 (n-6) PUFA in aquatic and terrestrial organisms. Higher total n-3 content compared with n-6 PUFA and a strong prevalence of the n-3 PUFA eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) characterized aquatic versus terrestrial organisms. Conversely, terrestrial organisms had higher linoleic acid (LNA) and alpha-linolenic acid (ALA) contents than aquatic organisms; however, the ratio of ALA:LNA was higher in aquatic organisms. The EPA + DHA content was higher in aquatic animals than terrestrial organisms, and increased from algae to invertebrates to vertebrates in the aquatic environment. An analysis of covariance revealed that fatty acid composition was highly dependent on the interaction between habitat and trophic level. We conclude that freshwater ecosystems provide an essential service through the production of n-3 LC-PUFA that are required to maintain the health of terrestrial organisms including humans.

Omega-3 long-chain polyunsaturated fatty acids support aerial insectivore performance more than food quantity

“…In the wild, aerial insectivores consume a combination of terrestrial and aquatic insects (18), which differ in their FA composition (19). Aquatic insects contain much higher levels of LCPUFA than do terrestrial insects, a difference driven by differences in the FA composition of aquatic and terrestrial primary producers (19,20).…”

“…Aquatic insects contain much higher levels of LCPUFA than do terrestrial insects, a difference driven by differences in the FA composition of aquatic and terrestrial primary producers (19,20). Aquatic primary producers, such as diatoms and dinoflagellates, are rich in EPA and DHA (21), which can be incorporated into aquatic insect tissue (22).…”

“…Aquatic primary producers, such as diatoms and dinoflagellates, are rich in EPA and DHA (21), which can be incorporated into aquatic insect tissue (22). In contrast, vascular terrestrial plants contain little to no LCPUFA but do contain their molecular precursor ALA (14), which can be either incorporated into tissue or converted to LCPUFA to a minor degree by terrestrial insects (19). As a consequence, from the perspective of LCPUFA content, aquatic insects may constitute a higher-quality food for aerial insectivores than do terrestrial insects.…”

“…However, because both aquatic and terrestrial insects contain ALA, the relative value of aquatic insects depends on the capacity of aerial insectivores to convert ALA into LCPUFA (19). The ability to elongate ALA into LCPUFA varies greatly across taxa: Strict carnivores, such as cats (23,24), and animals from environments rich in LCPUFA, including most marine fish (25), have lost the ability to elongate ALA into LCPUFA and must obtain them directly from diet.…”

Browning reduces the availability—but not the transfer—of essential fatty acids in temperate lakes

“…Allochthonous DOM is enriched in long-chain saturated fatty acids (LC-SFA), fatty acids without double bonds and with 20 or more C atoms in their chains, but its PUFA content is restricted to mostly ω-6 (n-6) PUFA (Hixson, Sharma, Kainz, Wacker, & Arts, 2015;Taipale et al, 2014). In contrast, phytoplankton synthesise higher amounts of both n-3 and n-6 PUFA, although there are exceptions among taxa .…”