The image above is of a kelp bed. In ideal conditions, kelp can grow up to 18 inches per day. In stark contrast to the slow-growing corals, the giant kelp canopies tower above the ocean floor. Like trees in a forest, these giant algae provide food and shelter for thousands of fish, invertebrates, and marine mammal species. Storms and weather events, like El Niño, can tear and dislodge the kelp, leaving a tattered forest to begin its growth again each spring. Sea otters and sea urchins play critical roles in the stable equilibrium of this ecosystem. Sea urchins graze kelp and may reach population densities large enough to destroy kelp forests at the rate of 30 feet per month. Urchins move in herds, and enough urchins may remain in the location of a former kelp forest to stop any regrowth.

In the scenario above, identify the keystone and foundation species. Infer what might happen if the keystone species were greatly reduced.
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Keystone species is the sea otter. Sea otters, playing a critical role in containing the urchin populations, prey on urchins and thus control the numbers of kelp grazers to maintain the forest.

Keystone species is the kelp. If the kelp is reduced or destroyed the basis for the entire ecosystem is destroyed as is the ecosystem.

Keystone species is the kelp. It is the foundation for this ecosystem. If destroyed it would be replaced by another producer to establish a different ecosystem.

Keystone species is the sea urchin. If the sea urchin species is greatly reduced by an increase in the sea otter population, the kelp beds would continue to grow unchecked and other populations of herbivores would grow.