Correct Option (D)
Statement 3 is correct. The passage explicitly defines a keystone species as one that influences "the flow of energy and materials through ecosystems." It then identifies the sea star Pisaster ochraceus as an example of a keystone species. Therefore, it is directly implied that sea stars constitute an important component in the energy flow within the intertidal ecosystem.
Incorrect Options:
Statement 1 is incorrect. The passage states that mussels (Mytilus californianus) are dominant competitors that "crowd out other competitors" for space in the intertidal zone. Sea stars, however, are described as predators of mussels, consuming them to create bare spaces. Their relationship is one of predation, not competition between mussels and sea stars themselves.
Statement 2 is incorrect. The passage focuses on the ecological role and impact of sea stars as a keystone species within their ecosystem. It does not provide any information or discussion regarding the evolutionary history, developmental stages, or "climax of evolution" of sea stars. This statement is an unsupported generalization outside the scope of the provided text.