Slide 10 of 17
Notes:
Corals obtain their food in three ways. One is through zooxanthellae photosynthesis.
Photosynthesis, as you may remember, is the process plants use to convert trapped sunlight energy, water and
carbon dioxide into oxygen and carbohydrates (sugar). The zooxanthellae take in carbon dioxide through
photosynthesis, and then give off oxygen as a by-product that is used by the host polyp. Both oxygen and
carbohydrates are essential elements in the energy production of corals. Algae ãleakä these elements into the polypâs
tissue where they are absorbed and used for energy production. Besides playing an important role in coral nutrition,
zooxanthellae are also essential in the process of skeleton deposition. The polyp, on the other hand, provides protection
Corals also obtain their food through more active means. They prey on different types of algae called zooplankton and
phytoplankton. These microscopic algae generally float in the water, although some are able to swim short distances,
migrating from the bottom of the reef during the day, and back up to the top at night. This is why feeding, for most marine
Organisms, is much more active at night.
The corals ãcome aliveä at night, eating by extending tentacles to capture their prey. The coral nematocysts
sting and immobilize their prey so that the tentacles can withdraw and bring the food down into digestive cavity
of the polyp. Polyps can also release mucus in the form of thin sheets over the whole colony or in strands or sheets into
the water. Plankton, bacteria and organic debris get stuck to mucus and, the cilia on the tentacles help to bring
the mucus back into the digestive cavity.
The third way corals obtain food is through the absorption of dissolved organic molecules (DOM), particulate organic
material (POM), and from sharing of food. For example, DOM such as glucose and certain amino acids can be absorbed
from water through the polyp's body wall by means of tiny fuzzy projections called "microvilli.ä These organic molecules
enter the water column from decomposing animals and plants. Particulate organic material, such as bacteria, decomposing
organic matter and fish fecal material (detritus), are directly ingested by the polyp. Food can also be shared in some species
of colonial corals whose digestive cavities are interconnected Thus, food obtained by one polyp can be transported throughout
it's own body or to other polyps.
