Young sea otter being cleaned by its mother, Ucluelet, British Columbia, Canada – Kieran Wood, Unsplash
Sea otters, like other apex predators such as wolves, function at the top of the food chain, causing trophic cascades that affect the flow and storage of atmospheric carbon. One of their main prey species is the sea urchin – a spiky, globular echinoderm that can rapidly sweep across the seabed and consume entire forests of kelp. By keeping urchin populations in check, sea otters allow such forests to flourish and lock up more carbon.
Kelp forests guarded by sea otters can absorb 12 times more CO2 than unguarded forests
Michael Steinman, Unsplash
Protecting sea otters in coastal kelp forests between southern British Columbia and the Aleutian Islands can sequester 5.2 MtCO2 per year. That’s 8% of the total greenhouse gas emissions by British Colombia in 2021 (62 MtCO2e) ¹
Researchers estimate that coastal ecosystems, rich with marine plants such as mangroves and seagrass, sequester as much as 20 times more carbon per hectare than forests. Using carbon from the atmosphere to grow leafy structures underwater, kelp forests are indeed one of the most efficient absorbers of atmospheric CO2.
But unlike mangroves and seagrass, kelp usually grows near the shore in rocky and eroding conditions, where plant material cannot get buried. Instead, pieces of kelp are eventually transported to the deep sea, where the carbon can be sequestered in marine sediment, far removed from the atmosphere.
A 2012 study on North American sea otters found that kelp forests guarded by sea otters can absorb 12 times more CO2 than unguarded forests, with the marine mammals supporting the storage of up to 8.7 million tonnes of carbon by kelp every year. This roughly equates to the annual CO2 emissions of 4 million passenger cars, and means North American sea otters perform a carbon capture service worth up to US$400 million a year.
The results of the sea otter study suggest that predators can strongly influence the carbon cycle through top down forcing and trophic cascades. The extent to which these effects can be extrapolated across species and global ecosystems is yet to be fully determined, but it is clear that the restoration of predator populations has the potential to significantly influence the concentration of atmospheric CO2.
Moreover, the role of the sea otter in mitigating climate change demonstrates how easily the benefits that humans derive from healthy ecosystems – such as carbon sequestration – can diminish as our own actions negatively impact biodiversity. Hunted to near extinction in the eighteenth and nineteenth centuries, sea otters are currently endangered across their range, with pollution and habitat loss major factors in their decline. A decline that impairs our own ability to address the climate crisis.
The global decline in predators – and wildlife populations in general – is worrying. Yet their critical role in governing the global carbon cycle also offers hope. The very significance of animals in the cycle means that protecting, restoring and managing biodiversity is a feasible, immediate and potentially game-changing way of managing the global carbon budget and addressing our climate emergency.
Otter infographic based on oroginal design by GRID-Arendal
How do the sea otters help store carbon?
- Control Sea Urchin Populations: Sea otters prey on sea urchins, preventing them from overgrazing kelp forests, which helps maintain healthy kelp ecosystems.
- Promote Kelp Growth: With fewer sea urchins, kelp forests can thrive, growing larger and absorbing significantly more atmospheric carbon.
- Increase Carbon Sequestration: Kelp forests guarded by sea otters can absorb up to 12 times more CO2 than unguarded areas, storing carbon in their biomass.
- Support Long-Term Carbon Storage: Kelp that breaks away from coastal forests is transported to the deep sea, where carbon can be sequestered in marine sediment.
Current situation – what we need to do
The decline of sea otter populations has negatively impacted coastal ecosystems, reducing the carbon-sequestration capacity of kelp forests. To address this, we must focus on protecting and restoring sea otter populations, particularly in regions where kelp forests play a significant role in carbon storage. This includes addressing habitat loss, pollution, and other human impacts, as well as recognising the broader ecological and climate benefits that sea otters provide.
Protecting sea otters can be a crucial step in using natural ecosystems to combat the climate crisis.
Kelp – Shane Stagner, Unsplash
(1)Note: These species data are from Table 1 and the Supplementary Appendix 1 of Schmitz, O.J., Sylvén, M., Atwood, T.B. et al. Trophic rewilding can expand natural climate solutions.
Nat. Clim. Chang. 13, 324–333 (2023). https://doi.org/10.1038/s41558-023-01631-6
Next steps
- Return to the main Climate Heroes page.
- Read all the original Climate Hero case studies in ‘Animating the Carbon Cycle: Supercharging Ecosystem Carbon Sinks to Meet the 1.5°C Climate Target’. Download the pdf here.
- Curious to learn more? Watch the video from the UN Climate Change Side Events at COP28: Bringing elephants into the room – why UNFCCC needs to put animals on the table.