Which of the following are examples of hard coral?

The selection of elkhorn and staghorn corals as examples of hard corals is accurate because both types are classified under the scientific category of scleractinian corals, which are known for their hard calcium carbonate skeletons. This characteristic is what distinguishes hard corals from soft corals, as hard corals contribute to the structural integrity of coral reefs.

Elkhorn corals (Acropora palmata) and staghorn corals (Acropora cervicornis) are essential reef-building corals that create complex habitats for numerous marine species. Their rigid structures provide both protection and feeding grounds for various fish and invertebrates, making them vital for maintaining the ecosystem's health and biodiversity.

In contrast, options that include sea fans and brain corals are examples of soft coral and other coral types that do not have the same hard skeleton structure as hard corals. Thus, understanding the fundamental difference between hard corals like elkhorn and staghorn and other corals is crucial for identifying and appreciating marine ecosystems.