Do Fish Eat Coral? The Complex Relationship Between Reef Fish and Corals

Coral reefs are some of the most biodiverse ecosystems on Earth, home to thousands of species of fish, invertebrates, and other marine life. At the foundation of these reefs are the corals themselves, which provide food, shelter, and nursery grounds for many reef inhabitants But with so many hungry mouths to feed on the reef, an important question arises do fish eat coral? The answer is complex, highlighting the intricate interdependencies that exist between corals and reef fish

Some Fish Do Indeed Eat Coral

While not all reef fish eat coral, some species definitely do. Parrotfish and butterflyfish are two groups well known for their corallivorous habits. Parrotfish like the bumphead parrotfish use their beak-like jaws to take bites of coral, ingesting both the coral polyps and the calcium carbonate skeleton. They then grind up and excrete the calcium carbonate as fine sand, helping shape the physical structure of the reef.

Butterflyfish are pickier eaters, nipping off coral polyps but generally avoiding the skeleton By selectively feeding on fast-growing corals, butterflyfish prevent these competitive corals from overrunning slower-growing species, thus maintaining high coral diversity. Species like the orbiculate batfish even feed exclusively on Acropora corals

Other, less specialized fish like some angelfish, tangs, triggerfish, and pufferfish may occasionally nip at coral but generally aren’t reliant on it. Nonetheless, these fish can still inflict damage, especially on branching corals. Experts estimate that parrotfish alone are responsible for 5–10% of annual coral loss on Caribbean reefs.

Why Do Fish Eat Coral?

Coral polyps are nutritious, containing proteins, fats, and carbohydrates. For some fish, they may be the main diet. But there are other reasons fish feed on coral:

• Source of Calcium: Coral skeletons are made of calcium carbonate. Fish like parrotfish ingest this material likely as a calcium supplement.

• Dental Hygiene: The calcium carbonate may help clean parrotfish teeth and strengthen jaws.

• Gain Access to Prey: Butterflyfish nip at coral to expose tasty shrimp and other invertebrates living inside.

• Control Algal Growth: By reducing coral cover, parrotfish prevent fast-growing coral species from overtaking algae-eating zones.

So in some cases, eating coral provides nutrition, while in others it serves a secondary role. Nonetheless, unchecked coral predation can damage reefs.

Coral Loss Harms Reef Fish

When corals die off due to bleaching, disease, storms, or other disturbances, the reef ecosystem suffers—reef fish included. Corals support the ecosystem in the following ways:

• Shelter: Corals provide small spaces for fish to hide from predators and lay eggs. Some fish even secrete mucus cocoons for protection while resting in corals overnight.

• Food: Reef fish graze on the plankton caught by corals and feast on invertebrates living on corals. Some juveniles start life feeding on coral mucus and polyps.

• Recruitment: Many fish larvae seek out coral reefs to settle because corals signify plentiful food. Without living corals, the cues for larvae to settle go away.

On degraded reefs lacking coral structure, fish diversity and abundance declines. Juvenile fish disappear without nursery habitats. Predation risk goes up with fewer hiding spots. Food sources dwindle as corals die. Entire reef fish assemblages shift to smaller bodied, shorter-lived species.

Balance is Key in the Coral-Fish Relationship

Corals and coral reef fishes clearly rely on each other, exhibiting a delicate balance of give and take. Corals provide food and shelter to fish but can only withstand limited predation. Fish obtain nutrition from corals but depend on live coral for their survival.

To maintain equilibrium, herbivorous and corallivorous fish must feed at sustainable levels. A diverse reef fish community with ample algae grazers also prevents seaweed from smothering recovering corals after disturbances. Removing top piscivorous predators like sharks can disrupt this balance by causing mesopredator fish to overpopulate and decimate their coral prey.

By understanding these complex interrelationships, researchers can better predict how reef ecosystems will fare in the face of growing human impacts. If we wish to conserve coral reefs for future generations, maintaining healthy fish populations and their connections to coral will be key. Corals and fish sustain each other—lose one, and the entire ecosystem suffers.