The coral reef food chain
For a coral reef to stay healthy it needs inhabitants from each level of the food web. That starts with the photosynthetic organisms such as seaweed and zooxanthellae (algae). A reef that is overrun with algae is probably not healthy because the primary consumers of algae are missing. Crabs, sea urchins and sponges all feed on algae. So do some sea turtles, parrot fish and surgeon fish. Remove one of these creatures from a reef and algae growth can get out of control.
Next up the reef food chain are the carnivorous fish classified as secondary consumers. These include wrasse, butterfly fish, file fish, trigger fish and goat fish. These small fish eat corals as well as worms, sea snails and crustaceans. You will see these fish picking at a reef like a bird pecks at food. Or, like goat fish, rummaging in the sandy sea bed.
At the top of the reef food chain are the tertiary consumers, the bigger animals that feed on smaller fish and crustaceans. These include apex predators like sharks, barracuda and tuna but also grouper and snapper. These are the fish that are commercially fished at unsustainable levels. Without their presence on a reef the whole delicate ecosystem is in danger.
With fish stocks around the world close to collapse we need to reevaluate our own place in the marine food chain so that we can co exist with ocean inhabitants.