Seaweeds and Sea Otters

Seaweeds and Sea Otters

Seaweeds and sea otters have a symbiotic relationship as evidenced by the rafts of sea otters (Enhydrus lutra), numbering in the hundreds, bobbing amongst the kelp beds just north of Tofino in Kyuquot Sound, Vancouver Island. These furry creatures are closely intertwined with the life cycle and recovery of kelp forests from urchin predation. Once an endangered mammal and hunted for their fur to the brink of extinction, they have made remarkable recoveries since reintroduction between 1969 and 1972; eighty-nine otters from Alaska were reintroduced to Checleset Bay (Gregr, 2016)(Groc, 2018) and now seven thousand reside there (Ogden, 2020). Some are even seen as far south as Point No Point and Victoria. However, First Nations were never consulted in this process, and the sea otter return sparks controversy over the decline of sea urchin, Dungeness crab and shellfish fisheries (Gregr, 2016).

seaweeds and sea otters, rafts of sea otters
Rafts of sea otters

Sea otters are a keystone specie

Sea otters are a keystone specie and their resiliency result from their diversity of prey and ability to learn in a social network (Ogden, 2020).  They prey predominately on sea urchin which then releases kelp forests from sea urchin predation (Gregr, 2016). This then triggers a trophic cascade of growth for kelp forest ecosystems including reef fish, shore birds, and coastal wolves. Kelp forests encourage organism growth through creation of complex habitats, modifying nearshore currents and providing nutrient pumps for all (Markel, 2006). The other beneficial factor is that kelp forests provide carbon sequestration and thus, mitigate climate crisis.

Sea otters and Perennial Kelp

seaweed and sea otters, macrokelp
Perennial kelp such as macrocystis grown back when sea otters return

When sea otters return to an environment, more robust species of kelp including perennial kelps such as macrocystis return where annual kelps such as nereocystis once grew (Watson, 2011). Also, certain species of birds such as oyster catchers and harlequin ducks benefit  from sea otter return. The oyster catchers prey on invertebrates that grow on mussel patches pried off by sea otters. Whereas, the harlequin ducks benefit from the urchin scraps left behind by sea otters. This allows them to not only eat prey that otherwise lies too deep for them to forage but also survive the winter with the nutrition provided by sea urchins (Groc, 2018).

Opponents to sea otters

However, opponents to sea otter reintroduction argue that sea urchin, Dungeness crab and shellfish fisheries have all declined since their return (Gregr, 2016)(Groc, 2018). Sea otters primarily prey on sea urchin and as sea urchin abundance declines, they then eat bivalves, snails, chitons, crabs, sea stars, and in some cases even fish (Gregr, 2016). Although 33% of geoduck grounds were closed in 2012 because of sea otter predation, this seems to be site specific (Gregr, 2016). Furthermore, data suggests that sea otters dive to only 50 metres to hunt their prey leaving the larger Dungeness crabs to grow at deeper depths (Gregr, 2016). There is a trade off for the loss of sea urchin and shellfish fishery with the gain in rockfish fishery, focus on eco-tourism and carbon sequestration (Gregr, 2016) (Gregr. et al., 2020). One model predicts that a sea otter-dominated system will produce between 30 and 90 million dollars per year more than one dominated by sea urchins, crabs and geoducks (Gregr, 2016). In fact, with fewer urchins grazing, underwater kelp forests have grown twenty-fold, providing new habitat for a range of fish from rockfish to salmon. Stocks of ling cod have tripled, and the overall amount of life in the water has increased by 37 per cent, which has created new fisheries worth nearly $10 million. Furthermore, more carbon sequestration can be worth about $2 million at current carbon prices (Gregr et al., 2020).

Eco-tourism for sea otters

Eco-tourism, particularly focused on sea otters, has increased in the past 20 years (Groc, 2018). This could translate to a 7.4% increase in tourists and an estimated $9.5 million per year in potential revenue for tourism operators (Groc, 2018). To date, tourists have spent a total of about $42 million for the privilege of seeing the otters raft and play (Gregr et al., 2020). However, efforts also should be made to encourage Indigenous communities as stewards for sea otter preservation. This may be difficult given that a whole generation has watched their shellfish stocks decline when sea otters were reintroduced (Groc, 2018).

Indigenous Shared Learning about sea otters

In fact, Anne Salomon, a socio-ecological systems researcher at Simon Fraser University in 2014 organized workshops bringing together archaeologists, scientists, leaders and representatives from 19 First Nations across British Columbia and Alaska to discuss otter, shellfish, kelp and human interactions. Together, they brainstormed coexistent solutions such as valuing indigenous knowledge, increasing indigenous authority and governance, and shared learning between indigenous communities around resource decision-making (Ogden, 2020).

In summary, kelp forests and sea otters are closely intertwined. Although colonial reintroduction of sea otters has resulted in regrowth of kelp forests and the ecosystems they support, the trade-off is the decline of sea urchin, Dungeness crab and geoduck fisheries. Despite this, there could be gain economically from rockfish fishery, eco-tourism and carbon sequestration. Furthermore, there must be recognition of the importance of the First Nations who have lived alongside otters for millennia and are threads intertwined into the rich fabric of Pacific coastal ecosystems.

References

Gregr, E.; Villy, C.; Nichol, L.; Martone, R.; Markel, R.; Watson, J.; Harley, C.; Pakhomov, E.; Shurin, J.; Chan, K. (June 12, 2020). Cascading social-ecological costs and benefits triggered by a recovering keystone predator. Science,368: 1243-1247. DOI: 10.1126/science.aay5342

Gregr, E. (Aug. 2016). Sea Otters, Kelp Forests, and Ecosystems: modelling habitats, uncertainties, and trade-offs. Doctor of Philosophy dissertation in UBC Dept. of Postdoctoral studies.

Groc, I. Visit Sea Otter Country (June 8, 2018). BC Magazine. Retrieved on 2018/07/05 from https://www.bcmag.ca/visit-sea-otter-country/

Markel RW (2006). Sea otter and Kelp Forest Recovery: implications for nearshore ecosystems, fishes and fisheries. Vancouver, British Columbia: Parks Canada. Report no. 5P429‐05‐007

Ogen, D. ( Aug. 2020). The Sea Otter Rescue Plan that Worked too Well. BBC Future Planet [online]. Retrieved 2020-12-23 from https://www.bbc.com/future/article/20200818-the-canadian-sea-otter-rescue-plan-that-worked-too-well

Watson, J. and Estes, J. A. (2011). Stability, Resilience, and Phase Shifts in Rocky Subtidal Communities along the West Coast of Vancouver Island, Canada. Ecological Monographs, 81: 215-239. doi:10.1890/10-0262.1