Herbivory in Tropical Reef Fish
Herbivores are essential in maintaining ecosystem health, particularly in tropical reef systems. Coral reefs are facing many challenges (global warming, coral diseases and predation, etc.) that may upset the natural balance of these ecosystems. Therefore it is important for us to understand the dynamics of these systems, even down to the fundamental level of intestinal microbes and their role in digestion in herbivores. A thorough knowledge of these complex interactions may help us identify and control critical factors that threaten these ecosystems.

Herbivory on Coral Reefs
Herbivores are an important part of coral reef ecosystems. They help to maintain the balance between corals and macroalgae on reefs. Macroalgae are extraordinarily fast growers and are generally less sensitive to changes in environmental factors, such as temperature and sedimentation, than coral species. For these reasons macroalgae have the potential to out-compete corals. However, consumption of macroalgae by herbivores limits their density, thus maintaining a healthy competition between the two groups. Reefs that lack the appropriate number of herbivores suffer greatly due to an overgrowth of algae. One of the most well known cases of overgrowth occurred in the Caribbean after a previously unseen disease virtually killed off the herbivorous sea urchin Diadema antillarum[i]. The mass decimation of this urchin caused an ecological collapse of Caribbean reefs, with macroalgae becoming dominant over coral species. This ecological shift has had a negative effect on the diversity and composition of Caribbean reef assemblages. This unfortunate event in the Caribbean demonstrates that herbivores and their ecological function are extremely important to the health of coral reefs around the globe. 

On coral reefs, there are both invertebrate and vertebrate herbivores. Invertebrate herbivores include urchins (see above), crabs, limpets, chitons, and polychaete worms. Prominent vertebrate herbivores can be reef fishes, sea turtles, and dugongs[ii].

[i] Knowlton, N. 2001. Sea urchin recovery from mass mortality: New hope for Caribbean coral reefs? Proceedings of the National Academy of Sciences 98(9): 4822-48244
[ii] Hay, M.E. 1997. The ecology and evolution of seaweed-herbivore interactions on coral reefs. Coral Reefs 16(Supp.1): S67-S76

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