Keystone species maintain order and uphold the balance in ecosystems. the shifting landscapes of Aleutian kelp forests suggest that keystone species may also help ecosystems cope with climate change.
Sea otters are renowned keystone species — by preying upon kelp-eating sea urchins, sea otters regulate urchin populations and protect the entire kelp forest ecosystem. When in the 18th and 19th centuries, sea urchins populations grew unchecked and decimated kelp forests. Kelp forests rebounded when sea otters were reintroduced, but sea otter populations are once again declining as the growing killer whale population — recovering from pre-industrial whaling — has added sea otters to their menu. In the absence of sea otters, sea urchin populations can once again flourish, jeopardizing kelp forest health.
The slow-growing, calcareous red algal species (Clathromorphum nereostratum) that builds the Aleutian kelp forests managed to survive destruction when sea otters were initially wiped out because its hard skeleton deterred sea urchin predators. But climate change has made the algae susceptible to over-grazing as warming water speeds up sea urchin metabolism and ocean acidification weakens the algae’s protective skeleton.
Aleutian kelp forests are rapidly declining due to combined effects from the restructuring of food webs and environmental changes. Based on models of sea otter abundance and sea urchin grazing rates on the red algae over the past 40 years, scientists suspect that kelp forest loss was initiated by the disappearance of sea otters and then worsened by environmental changes. If sea otters recovered, however, the researchers believe they would serve as a buffer — mitigating the detrimental effects of climate change on the kelp forest environment. It is possible that other keystone species could help lessen ecosystem changes in the face of rapidly changing environmental conditions.