The sea otter is the most likely to be a keystone species in the food web provided. Keystone species are typically predators that have a disproportionate impact on the ecosystem they inhabit. In this food web, the sea otter preys on sea urchins, which in turn feed on kelp. If the sea otter population were to decline, sea urchins would likely overgraze the kelp forests, leading to a cascade of negative effects on other species in the ecosystem. Therefore, the sea otter plays a crucial role in maintaining the balance of the ecosystem and is considered a keystone species.
