Both kelps and coral reefs are composed of algae that grow in the shallow parts of the ocean in warm and sunny waters. However, kelp forest grows in nutrient-rich waters while corals can develop in low nutrient waters.
Kelp forests are therefore common where warm and cold current meet in an up-welling. Coral reefs are borne of a symbiotic relationship between coral polyps and algae. The coral forms a rigid carbon skeleton of calcium carbonate while kelps are long flexible algae plants.
