Assertion: Aquatic herbivores are usually more productive as compared to terrestrial herbivores.
Reason: Phytoplanktons achieve faster grwoth rate and more nutritous to heterotrophs than their terrestril counterparts due to their small size and lack of structural tissues.

Answer: ASolution: Most plant material is not consumed or is not digested by terrestrial herbivores, because plants have so much structural material. Most algal material (phytoplanktons) is consumed and digested by aquatic herbivores, because algae have very little structural material. Moreover, phytoplanktons turn over much more rapidly than terrestrial plants, so biomass at any given time is low as compared to the productivity. Phytoplanktons grow and reproduce rapidly, so a small mass can have a faster rate of primary production. In contrast, terrestrial primary producers grow and reproduce slowly. Thus, terrestrial herbivores are less productive than aquatic herbivores.