In aquatic systems, why is assimilation efficiency higher?
Aquatic primary producers, especially phytoplankton, are often highly digestible because they contain little cellulose, lignin, or long-lived support tissue. Consumers can therefore absorb a large fraction of ingested material, producing higher assimilation efficiency than herbivores feeding on woody or fibrous terrestrial plants. The mechanism is food quality, not simply oxygen supply or species diversity. Aquatic detritus and heavily defended algae can be poorly assimilated, so the pattern is strongest when comparing zooplankton–phytoplankton links with terrestrial herbivory. Decomposition r
Ref: Fundamentals of Ecology, Odum & Barrett, 5th Ed., Ch. 3