CREATURES OF THE CORAL REEF
Objective: Understand the role plankton has in the coral reef ecosystem.
Vocabulary: non-living things, living things, plankton, phytoplankton,
zooplankton, producers, photosynthesis, consumers
Ocean waters contain many non-living and living things that are not visible to the
human eye. Some of these non-living things are dissolved substances called salt and
limestone. Tiny plants and animals that float in almost all bodies of water called plankton
are some of the many living things existing in the ocean that are small and
difficult to see. Despite their small size, plankton plays an extremely important role in
supplying food not only to the coral reef system but the entire ocean ecosystem.
Although there are many different kinds and species of plankton, they can easily
be grouped into two basic types: plants and animals. Plankton that are plants are called
algae, or phytoplankton. Plankton that are animals are called zooplankton.
Phytoplankton are producers. This means that in the process called photosynthesis,
they produce their own food using sunlight, water, carbon dioxide, and nutrients.
As animals, zooplankton are consumers and as a result must capture their food.
Look at the drawings above and notice that zooplankton have various food capturing devices
in the physical appearance whereas phytoplankton do not.
Using the process of photosynthesis, phytoplankton rely on the sunlight energy
that passes through the surface of the water to live in the ocean. For this reason
phytoplankton, or algae as its commonly called, lives within few meters of the surface of
the water where there is plenty of sunlight. Shallow ocean waters that are abundant in
algae are usually greenish in color.
There are many different species of phytoplankton algae that grow in the ocean and that
are eaten by small fish and other marine organisms. Certain species of algae called zooxanthellae,
that has a symbiotic relationship with corals as it lives inside the body of coral polyps
providing them with food and skeleton building capacities. Similar to other species that
float in the surrounding ocean water, zooxanthellae, uses sunlight and excess
nutrients from the coral polyps to grow.
Zooplankton capture the phytoplankton floating beside them in the water by using
various stinging and capturing techniques. Zooplankton are one of the important
foods of coral polyps.
Both phytoplankton and zooplankton are very important in both coral reef and ocean
ecosystems because they form the bottom of the food chain. This means that because
plankton are the food that small marine animals, fish, coral polyps and other marinelife
eat, they also support larger fish and other animals higher in the food chain. The larger
fish and other animals are often eaten by humans. In this way humans, who are at the top
of the food chain are dependent on plankton, which are on the bottom.