You can tell that sea otters are a keystone species because their presence has a significant impact on the overall ecosystem. When sea otters were present in the ecosystem, the sea urchin population decreased, which allowed the kelp population to increase. When sea otters were removed from the ecosystem, the sea urchin population increased, leading to a decrease in the kelp population. This shows that the presence of sea otters has a cascading effect on the ecosystem, highlighting their importance as a keystone species.
