Dugong (Dugong dugon) feeding on seagrass, Northern Red Sea, Egypt
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An herbivore is an organism that feeds on plants. These organisms are referred to as herbivorous. An example of a marine herbivore is the manatee.

The opposite of an herbivore is a carnivore or 'meat-eater.'

Origin of the Term Herbivore

The word herbivorous comes from the Latin word herba (a plant) and vorare (devour, swallow), meaning "plant-eating."

Size Matters

Many marine herbivores are small because only a few organisms are adapted well enough to eat phytoplankton, which provides the bulk of the "plants" in the ocean. Terrestrial herbivores tend to be larger since most of the terrestrial plants are large and can sustain a large herbivore.

Two exceptions are manatees and dugongs, large marine mammals who survive primarily on aquatic plants. However, they live in relatively shallow areas, where light is not limited and plants can grow larger. 

Advantages and Disadvantages of Being An Herbivore

Plants such as phytoplankton are relatively abundant in ocean areas with access to sunlight, such as shallow waters, at the surface of the open ocean, and along the coast. So an advantage of being an herbivore is that food is pretty easy to find. Once it is found, it can't escape like a live animal could.

On the disadvantage side, plants are more difficult to digest and more may be needed to provide adequate energy for the herbivore.  

Examples of Marine Herbivores

Many marine animals are omnivores or carnivores. But there are some marine herbivores that are well-known. Examples of marine herbivores in various animal groups are listed below.

Herbivorous Marine Reptiles:

  • Green sea turtle (who are named for their green fat, which is green because of their plant-based diet)
  • Marine iguanas

Herbivorous Marine Mammals:

  • Manatees, as already mentioned above.
  • Dugongs

Herbivorous Fish

Many tropical reef fish are herbivores. Examples include: 

  • Parrotfish
  • Angelfish
  • Tangs
  • Blennies

These coral reef herbivores are important to maintaining a healthy balance in a reef ecosystem. Algae can dominate and smother a reef if herbivorous fish aren't present to help balance things out by grazing on the algae. Fish can break down the algae using a gizzard-like stomach, chemicals in their stomach and intestinal microbes.

Herbivorous Invertebrates

  • Some gastropods, such as limpets, periwinkles (e.g., the common periwinkle), and queen conchs.

Herbivorous Plankton

  • Some zooplankton species

Herbivores and Trophic Levels

Trophic levels are the levels at which animals feed. Within these levels, there are producers (autotrophs) and consumers (heterotrophs).  Autotrophs make their own food, while heterotrophs eat autotrophs or other heterotrophs. In a food chain or food pyramid, the first trophic level belongs to the autotrophs. Examples of autotrophs in the marine environment are marine algae and seagrasses. These organisms make their own food during photosynthesis, which uses energy from the sunlight.

Herbivores are found at the second level. These are heterotrophs because they eat the producers. After herbivores, carnivores and omnivores are at the next trophic level, since carnivores eat herbivores, and omnivores eat both herbivores and producers.

References and Further Information

  • Cornell University. Herbivory in Fish. Accessed October 31, 2015.
  • Harper, D. Herbivorous. Online Etymology Dictionary. Accessed October 1, 2015.
  • National Geographic. Autotroph. Accessed September 29, 2015.
  • Map of Life. Gut fermentation in herbivorous animals. Accessed October 31, 2015.
  • Morrissey, J.F. and J.L. Sumich. 2012. Introduction to the Biology of Marine Life. Jones & Bartlett Learning. 466pp.