Fig. 2: Marine, freshwater, and terrestrial organisms differ in their fatty acid composition, especially in terms of the omega-3 PUFA ALA, EPA, and DHA. These ecosystem-based differences are most pronounced in (A-C) primary producers, but also occur among (E-F) higher order consumers. (A-C) Vascular terrestrial primary producers contain only the shorter-chain omega-3 PUFA ALA, while aquatic primary producers, as well as a few non-vascular terrestrial primary producers like Bryophytes, also contain the longer-chain omega-3 PUFA EPA and/or DHA. (D-F) Consumers contain more EPA and/or DHA than primary producers from the same ecosystem, but also exhibit differences based on both ecosystem (e.g., terrestrial versus marine mammals and terrestrial versus freshwater insects) and trophic position (e.g., fish versus insects or Cladocerans).