Description of the ecosystem: 

The multiple features of this ecosystem are that it's a haven for all kinds of sea creatures that provides shelter and food. It is referred to as the cities of the sea or rainforests of the sea with how one-quarter of all ocean species depend on reefs. The key characteristics of coral reefs are that they are related to sea anemones as they all share the same simple structure, the polyp which is their mouth used to eat surrounded by a ring of tentacles. Their tentacles have stinging cells which are called nematocysts, that allow them to capture small organisms that swim by them. Inside the polyps are digestive and reproductive tissues that help them eat and protect their internal organs. Also, Corals differ from sea anemones as their mineral skeleton is different. 

The mineral skeletons they have are made up of different materials depending on what species they are. But mostly it is calcium carbonate which is found in each polyp like on stony species such as the organ pipe corals, precious red corals, and blue corals. Others like sea fans, sea rods, rubbery soft corals, and black corals use more flexible materials or tiny stiff rods to build their skeletons. 

As for what shallow coral reefs in warmer waters eat, they have another advantage as well which is zooxanthellae. They are single-celled algae that photosynthesize in the coral polyps to pass some of the food they get from the energy of the sun to their hosts, the corals. The coral then exchanges with the algae by giving nutrients. It is a symbolic relationship that allows shallow water corals to grow at a rapid rate to build enormous structures that we call reefs. (Shown in the right picture below is a close-up of the algae). Also, a fun fact the zooxanthellae provide the coral colors we see such as green, brown, and reddish tones. The less common colors of purple, blue, and mauve are the ones that the coral makes itself.

(©UNEP World Conservation Monitoring Centre/Global 1KM Version 7.0 Dataset)

What are the key organisms that live in this community? Why are they important?  How have they adapted to live in this environment?

One of the organisms that live in this ecosystem is Parrotfish which eat the reef itself. As they break at the coral to get small algae like the zooxanthellae that live inside the coral polyps, then they grind them up with teeth in their throats and turn them into sand. Other species have a role of cleaning such as “Cleaner” fish and shrimp that keep other fish healthy by getting rid of parasites. As crabs and sea cucumbers crawl around to scavenge and clean up detritus on the reef and ocean floor like janitors. Also, snails and worms have an important role in coral reef ecosystems with snails grazing on the algae while worms filter the water from organic matter and sediments. Other species that filter the water include sea squirts, salps, and giant clams which sieve and eat the phytoplankton. Sea sponges are also important to reef health as they provide a habitat for crustaceans, marine worms, young fish, barnacles, and tiny mollusks in their intricate canals and help filter the water as well. So the filtering species are referred to as “recyclers”. Lastly, Sea anemones formed symbiotic and beneficial relationships with the fish and crabs in the coral reefs. They hide and protect them while the fish and crabs protect the anemones in return. 

What key inter-relationships exist between organisms (food web, predator-prey, producers)?

Each species in the coral reefs plays its own function in this ecosystem as the herbivore species specialize in eating different kinds of algae to keep corals from being smothered by other potentially deadly competitors. As for carnivores like sharks, groupers, and other predatory fish, they keep the populations of smaller fish and other organisms in balance so it doesn't overpopulate.