Written by Amy Barker
If you have an interest in marine conservation you are likely to have heard the story of the southern sea otter (Enhydra lutris nereis), the ‘keystone’ species that restored an entire ecosystem along the California coastline. For those of you who have not encountered this story before, or whose memory is a little patchy, I will recap the basics. The sea otter distinguishes itself from other marine mammals in its evolutionary strategy of extremely dense fur as opposed to blubber in order to survive in freezing ocean temperatures. With one million hairs per square inch they have the densest fur of any mammal, a distinction which sadly left the species highly sought after by hunters. They were left almost extinct by the 1920s, and the ecosystem within their former range was in turn left devastated by their decline. Sea otters are major predators of sea urchins and other invertebrates which feed on the giant kelp, which forms underwater ‘forests’ of vital habitat for a great abundance of biodiversity. These forests also share an important function with forests found on land – they absorb vast quantities of carbon dioxide, and unlike those on land, they also protect the coastline from storm surges. Without these top predators, numbers of kelp feeders grew exponentially, and the kelp forests quickly disappeared, along with the diversity of species that were dependent on it. Sea otter numbers are still not what they were, but along the California coast and particularly in the Monterey Bay, where a large proportion of the species resides, their numbers are now sufficient to maintain the forests that dominate the coastline once again. Their total population has grown from around 50 in 1911 (when the hunting ban began) to around 3000 today, although their range remains a fraction of what it was.
You may have heard of this story as one of the more striking examples of a keystone species at work, or you may know it better as one of the great conservation success stories. It seems to support a popular philosophy in conservation that put simply is ‘if you leave nature alone it is sure to bounce back’. Although it is astonishing how the kelp forests in Monterey Bay appeared to resurrect alongside the sea otter, it is important to remember that there is no guarantee of the continued persistence of either. Sea otters today face threats, both new and old to them, that are totally unrelated to the hunting ban. There is much more to this story, and extensive research has propelled our understanding of the species and informed further conservation efforts. We know more about their ecological role and the new threats that they face, and new strategies are being employed to ensure their continued success. So, here is a reprise therefore on the classic tale of the Southern Sea Otter, a species that is so much more than a ravenous urchin consumer (which is important too of course!).
read more The Sea Otter Story