The sea otter is most likely to be a keystone species in the provided food web. Keystone species play a crucial role in maintaining the structure and functioning of an ecosystem. In this food web, the sea otter preys on sea urchins, which helps control the sea urchin population. This, in turn, prevents the overgrazing of kelp forests by sea urchins, allowing other species in the food web to thrive. Therefore, the sea otter is a keystone species in this ecosystem.
