In southern California, giant kelp beds were common until the 1950s. Changes in water conditions and the near extinction of the southern sea otter due to over-harvest resulted in a population explosion of the purple sea urchin. The size and number of local kelp beds were reduced severely for several years. After they eat all the kelp in an area, they can live for decades with little food there.
To replace the otter’s role in the ecosystem, volunteer scuba divers have systematically, by hand, relocated thousands of urchin from the coastal waters to areas further out. With less predators eating it, plumes of giant kelp have thrived. With the kelp, other life has flourished off of Palos Verdes. Kelp bass, rock fish, giant kelp fish and many species of invertebrates have made a visible comeback. Due to restoration efforts, kelp forests have recovered along Palos Verdes.
Disappearing vast areas of kelp forests in the sea otters range (including Northern Japan, Alaska and Western North America) has been directly linked to the removal of sea otters. This in turn led to a sea urchin bloom once their main predator was removed. The sea otter is a keystone species in these kelp forests – a species that is crucial in controlling the food web. There have been similar kelp forest declines when other top predators such as fish and lobsters were removed.
Whilst the giant kelp forests of Tasmania’s east coast have now been listed by the Federal Government as an “endangered ecological community”, the listing offers no real help for the kelp whose demise is largely due to temperature and nutrients. It is an unfortunate example of how small changes can have a massive impact on the balance of our complex ecosystems.
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