The Rainforests of the Sea: Coral Reef Ecosystems

By: Ashley Gustafson


Every organism has an important role when it comes to making an ecosystem successful. Since coral reefs have achieved the prestigious title of “Rainforests of the Sea” they are known for their successful ecosystems and thus diversity earning them their nickname. Ecosystems are delicate structures that require a strong foundation of energy and interactions between different organisms. These relationships between organisms can range from just a handful of different organisms to hundreds of organisms like exhibited with coral reefs and rainforest ecosystems. One of the reasons coral reefs are so successful and thus so diverse is their high productivity. In order to understand this success it is important to understand how energy flows in ecosystems and how to interpret a food chain diagram.

How does a coral reef ecosystem work?

Ecosystems are simply defined as diverse groups of different species that interact with each other and share a physical environment. Coral reef Ecosystems have a variety of plants, animals, and bacteria that all live in harmony with each other. These wide varieties of organisms have specific roles in the ecosystem as a unit. Food chains or food webs are diagrams that sc

ientists can use to help visualize the relationships of these organisms and the energy flow within an ecosystem. Food chains consist of a variety of herbivores, carnivores, omnivores, and detritovores that exhibit producer, decomposer, and consumer relationships as well as predator/prey relationships. These relationships are connected through arrows which also convey the direction of energy flow through the ecosystem.

To organize these relationships, scientists have named these different types of organisms into trophic levels or positions in the food chain. The higher trophic level organisms feed on the lower trophic level organisms. The producers are the lowest trophic level in a coral reef ecosystem and are photosynthetic organisms like plants. An example of a coral reef plant is the seaweed species limu. While the consumers in a coral reef ecosystem are omnivores, carnivores, and herbivores. Consumers vary in trophic level with top predator carnivores being higher than herbivores and omnivores. Finally, the detritovores in a coral reef ecosystem are the scavengers and decomposers which specially digest decaying matter. Bacteria are important decomposers because by breaking down decaying matter they help recycle nutrients like nitrogen, carbon, and phosphates back into the coral reef environment.

Where does the energy flow in ecosystems come from?

Figure 1. Coral Reef food web

It is a widely well-known fact that all living organisms require energy to live and survive. This includes simple involuntary tasks such as breathing to voluntary, complicated motor skills like running or jumping. Organisms require energy to grow, move, and reproduce. The major energy source for the majority of ecosystems around the world is the sun. This is why coral reefs flourish and nearly always exist in shallow water where the producers can get the light they need to photosynthesize. Photosynthetic organisms, like coral reef plants, are the pivotal producers that provide the foundation of energy that flows through the rest of the ecosystem. This is why you don’t see many plants in deep water where photons, or light particles, can’t transcend. Other examples of producer organisms can be phytoplankton and algae which are also photosynthetic and able to convert sunlight directly to energy. On the other hand, consumers are not able to make their own energy so they must obtain it by consuming other organisms with energy. Primary consumers consume producers directly. Secondary consumers will consume primary consumers and/or producers. Tertiary consumers will consume primary or secondary consumers and/or producers. As you can imagine, many consumers don’t consume only one other organism so that is why many food chains or many arrows create a food web and show many relationships and many energy paths within an ecosystem. Thus, the more organisms there are in an ecosystem, the more complicated the food web. As one can imagine, an entire, detailed food web for a coral reef ecosystem can get quite complicated. It is also completely possible for an organism to portray more than one role. For example, a queen conch can be both a detritivore (decomposer) and a consumer. Consumers that eat only plants are called herbivores while consumers that eat only other animals are called carnivores because their consumption of carrion or flesh. Consumers that have combination diets and will consume both plant and animal matter are called omnivores.

As the law of the conservation of energy states, energy can neither be created nor destroyed. This is an important concept for energy flow withinany ecosystem. Since an organism uses roughly 90% of its energy for its own survival and only allows about 10% to return to the animal consuming it, the higher the trophic level the fewer organisms. To put this in practice, you can think of trophic levels as a pyramid. The bottom of a pyramid is wide and likewise the producers are the most plentiful in a healthy ecosystem. On the other hand, the top is narrow and supports only a few top level predators thus, in a healthy ecosystem the least plentiful organism is the apex predator. It is important when looking at trophic levels as a pyramid that the energy or arrows always travel up until returned to detritovores who recycle nutrients and energy back into the system. It is often easier to see this in action; reference the food chain diagram or figure 1. Scavengers and decomposers, while often an afterthought to many people, are an incredibly important part to the health of an ecosystem. As I previously stated they are vital for nutrient recycling. They also are good indicators of ecosystem health since they consume decaying matter. Usually when something is going wrong in an ecosystem, taking a look at the health of the detritovores is a good start to diagnosing a problem. The main decomposers in coral reef systems are bacteria. Coral reef ecosystems lacking these bacteria do not flourish and often the whole entire system crashes. Other examples of detritovores or scavengers in a coral reef ecosystem include gastropods like snails, crabs, sea cucumbers, and bristle worms.

Now I did not include algae as a decomposer which brings me to the question: Is algae a decomposer? It is a common misconception that algae is a decomposer within coral reef ecosystem. Algae is considered a producer in a coral reef ecosystem because they convert sunlight to energy, or they photosynthesize. Algae species are not consuming dead matter and recycling nutrients so they are not considered decomposers. Algae is a very important primary consumer as it is often the sole energy source for many primary consumers.

Coral Reef Video

Coral reef ecosystems are extremely complex, diverse, and magnificent ecosystems if balanced and efficient. It is no wonder that hundreds of species of organisms call its shelter home. A representative from nearly every type of marine organism you can imagine finds some sort of refuge in coral reef ecosystems. From phytoplankton to sea turtles coral reefs have a rich diversity unparallelled in other types of ecosystems. To conclude, enjoy this coral reef video as a summary and colorful adventure into the world of coral reef ecosystems.