Extinction of sea otters wrecks havoc on the entire ecosystem

it is very important to have a holistic view towards conservation of ecosystems. Losing a species may result in a domino-like effect, changing everything in that particular environment. For example, scientists are now looking at how the loss of sea predators, such as sea otters could devastate living reefs.

Sea otters help control populations of sea urchins that limit proliferation of corals. Image credit: Michael L. Baird via Wikimedia (CC BY 2.0)

For centuries Alaskan kelp forests were defined by living reefs. These magnificent limestone creations become home for so many different species. However, as reefs around the world are disappearing, Alaskan kelp forests are also suffering. They were here for centuries and now they are likely to collapse within several decades. And in part it is a result of changing composition of the entire ecosystem. The red alga Clathromorphum nereostratum, which basically underpins the Aleutian Islands’ kelp forest ecosystem, is being threatened by the growing population of sea urchins.

Sea urchins feed on red algae and generally are also a necessary part of every marine ecosystem. However, the problem is that their numbers are absolutely exploding out of proportion, because one of their main predators, Aleutian sea otters, became functionally extinct in the 1990’s. The population of sea urchins grew so much that these globular animals don’t have enough kelp to eat and, therefore, are now boring through the alga’s tough protective layer to eat the alga. This wouldn’t be so easy for them if not the climate change, which is causing ocean acidification, making corals easier to break down.

What happened to those sea otters? Oh nothing – they were hunted to near extinction during the maritime fur trade of the 1700s and 1800s. Their reduced populations survived for some time, but at the end of the last century sea otters were gone. Dr Nicholas Kamenos, one of the authors of the study, said: “Historic otter fur trading has led to previous reductions in otters and thus increases in urchin but the reef was not majorly affected. Things are different now due to the effects of climate change, and with a weakened skeleton, the urchins are having a large impact on the reef as otter numbers have lowered in recent years”.

Researchers analysed live Clathromorphum and urchins at the laboratory. Scientists found that lethal grazing under current conditions was about 35 to 60 % greater than in preindustrial conditions. Climate change and its effects on ocean acidification are also contributing to the rapid decline of coral reefs.

This just goes to show how huge human impact on various ecosystems can be. Removing sea otters encourages sea urchins to proliferate. They need to eat so they graze on the building blocks of coral reefs. Climate change makes it easier and soon enough thousands of species will lose their home that was full of life for centuries.


Source: University of Glasgow

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