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Sea otters help fight climate change

A recent publication has revealed the importance sea otters have in maintaining healthy and balanced ecosystems.

American marine biologist James Estes has recently unveiled that sea otters, marine mammals native to the coasts of the North Pacific Ocean, contribute to saving our planet.

His research, recently published in the book Serendipity: An Ecologist’s Quest to Understand Nature, observes wildlife behaviour through the interactions of predators with prey populations. Such synergies, called trophic cascades, helped Estes reveal the importance of predators in preserving healthy ecological ecosystems.

Sea otter floating on a bed of kelp off the coast of Alaska © Betty Wiley / Getty Images
Sea otter floating on a bed of kelp off the coast of Alaska © Betty Wiley/Getty Images

The origins of the study

Estes spent most of his career in the Aleutian Islands, located in the North Pacific Ocean and stretching from Alaska to Russia. Thanks to their remoteness, these lands remained unspoilt until two hundred years ago, though this changed with the arrival of fur trappers.

Sea otters, at the time thriving in numbers across the islands, were hunted for their thick and dense pelt and became close to extinction by the turn of the 20th century. This fate was overturned by an international ban, which saved the mammal from eradication and recovered its populations, although unevenly, across the archipelago.

Always interested in food-chains, Estes was intrigued by the impact that the near extinction of sea otters might have had on local ecosystems. He began comparing coastal areas where sea otters had survived with those where they had disappeared, and found that their ecological benefits go far beyond local ones.

The sea otter: a keystone species

Sea otters feed on sea urchins, crabs and other shellfish, cracking them open with stones before eating them. To survive, an adult sea otter needs to eat up to 38 per cent of its body weight due to very high metabolic rates. It is estimated that these animals spend from 24 to 60 per cent of the day foraging.

Through his study, Estes discovered that where sea otters were lacking sea floors were filled with urchins, which had eaten all the kelp. On the contrary, where sea otters thrived, urchins lacked and kelp flourished.

Black spiny urchins (Diadema sp.) graze on algae on a sand and rubble seafloor in Indonesia. Urchins are often found in disturbed areas due to algae being prominent there © Ethan Daniels/Stocktrek Images
Black spiny urchins (Diadema sp.) graze on algae on a sand and rubble seafloor. Urchins are often found in disturbed areas due to algae being prominent there © Ethan Daniels / Stocktrek Images / Getty Images

Kelp forests have the capacity of absorbing huge levels of carbon dioxide, whose impact has been increasingly harming the sea as well as the atmosphere. “Our results were eye-opening,” Estes told the Guardian. “The difference in annual absorption of atmospheric carbon from kelp photosynthesis between a world with and a world without sea otters is somewhere between 13 and 43 billion kilos (13 and 43 teragrammes) of carbon,” he continued. “Every species in the coastal zone is influenced in one way or another by the ecological effects of sea otters”.

Thanks to the observation of this and other trophic cascades, Estes has contributed to highlight the huge impact that apex predators have on the shape and functioning of our ecosystems.

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