Sea otters are keystone predators that maintain the dense, productive forests of kelp in coastal Alaska. Kelp forests are habitat for many invertebrates that are food for over 20 species of fish; these forests also provide spawning habitat for herring and Atka mackerel as well as nursery areas for salmon fry. Many birds, such as sea ducks, use them for resting and feeding. The forests of giant algal fronds protect the coastline from severe wave action and, like our land-based forests, absorb carbon dioxide from the atmosphere, helping to reduce global warming.