Final answer:
The killer whale is the organism that sits at the top of an energy pyramid, as it is an apex predator with no natural predators. It preys on other marine animals and represents a tertiary consumer in an oceanic food chain, above producers like algae, primary consumers like krill, and secondary consumers like leopard seals.
Step-by-step explanation:
The organism that would be found at the top of an energy pyramid is the one that is the apex predator within the ecosystem, meaning it has no natural predators and is at the end of the food chain. Among the options given, the killer whale (option 4) is the apex predator and would occupy the top of an energy pyramid, as it is known to prey on a wide range of species, including large mammals like seals. The energy pyramid illustrates how energy is passed up the food chain through different trophic levels: from producers to herbivores, then to various levels of carnivores, with each step resulting in a loss of energy.
At the base of the pyramid are the producers, such as algae, followed by primary consumers like krill, which are herbivores or omnivores. The next levels are occupied by secondary and tertiary consumers like the leopard seal, which predates on organisms like krill. However, the killer whale preys upon the leopard seal and other large organisms, positioning it at the apex of the food chain.
Important to note is that each trophic level consumes energy and only a fraction of the energy is transferred to the next level, which is why top predators like the killer whale are fewer in number compared to the organisms at the lower trophic levels.