Herbivorous fishes are fishes that eat plant material.Surgeonfish and parrotfish are two familiar MAR examples, often seen browsing and scraping on reef algae.

Herbivory is one of the most important processes in maintaining ecological balance on the Mesoamerican Reef. There, the primary herbivores are Diadema sea urchins (F12) and large (>30 cm) plant-eating fish. By grazing on non-encrusting algae,these herbivores help keep the algae in check, which in turn helps slow-growing corals to compete for limited reef space.

A change in herbivory rates—due to, for example,a decline in herbivore abundance—can rapidly lead to dramatic changes in reef appearance and function. If algae-eaters are too few in number, reefs once dominated by colorful corals can be quickly overgrown by fast-growing,fuzzy algae.

The abundance of herbivorous fishes depends in
part on the abundance and effectiveness of their predators. For some species, like the largest parrotfish (rainbow parrotfish), their abundance depends also on the availability of mangroves (S12) for critical nursery habitat.

One strong point of this indicator is that it is responsive to management action. For example ,if fishing pressure (one form of predation pressure) decreases,an increase in fish abundance will be observed (all else being equal).

We recommend tracking the fish component of herbivory by counting parrotfish and surgeonfish. Measuring herbivory rates directly is less practical,so
the next best thing is counting the fish.

A promising sign of Benchmark reef recovery would be a regional biomass of 2500 g/m2 for parrotfish and surgeonfish combined. In 1999-2000:9

• The regional average was 2110 g/m2 (33% of the
  Caribbean average).
• In Mexico,the mix was (in terms of biomass)
  50% parrotfish and 50% surgeonfish; in Belize,70%
  parrotfish and 30% surgeonfish