Iconic Kelp Forests

a pink and white leathery seastar in a kelp forest — Leather stars (*Dermasterias imbricata*) can be found along the West Coast, including in kelp forest habitats such as this one in Hopkins Marine Life Refuge. Photo: Chad King/NOAA

Kelp forests are among the most productive natural habitats with global rates of net primary productivity similar to tropical rainforests and estuaries. They provide services valued at $500,000–1,000,000 per kilometer of coastline (Filbee-Dexter and Wernberg 2018). For example, kelp is a “blue carbon” sink that contributes to climate resiliency by capturing carbon from the atmosphere and exporting the carbon to deep-sea environments for the long term. Kelp may also serve to buffer local ocean acidification effects and help local species/fisheries affected by increasing pH levels. Kelp forests are designated as a habitat area of particular concern for Pacific groundfish and salmon, and are critical habitats for supporting active fisheries on the West Coast.

Kelp forests cover nearly 25% of the world’s coastlines, primarily in shallow subtidal (less than 30 meters) rocky habitats in temperate and arctic regions (Schiel and Foster 2015; Wernberg et al. 2019). On the U.S. West Coast, the two major kelp species are giant kelp (Macrocystis pyrifera) and bull kelp (Nereocystis luetkeana). Bull kelp is more common at northern latitudes while giant kelp is more common at southern latitudes.

Benefits of Kelp

Kelp is a keystone species—providing foraging grounds, refugia, and nurseries, for numerous fishes and invertebrates (Wernberg et al. 2019). This includes the use by sea otters, who wrap themselves or their pups in kelp to minimize drifting while sleeping. Kelp forests increase local biodiversity; not just where kelp grows but through spill-over of individuals to other habitat types. Kelps are ecosystem engineers and structure the local ecosystems by altering a number environmental factors (e.g., wave action, light, pH, water flow).

Kelp forests also provide recreation and tourism benefits, including offering a scenic location and wildlife viewing opportunities for scuba divers and kayakers, as well as a place for recreational fishermen to catch fish (within and near kelp forests).

Concerns

National marine sanctuary staff are concerned about the recent loss of kelp forest cover in California and a co-occurring increase in abundance of purple sea urchins, which contribute to overgrazing kelp forests. The recent combination of multiple marine heatwaves, a sea star wasting disease outbreak, and increased herbivory by sea urchins contributed to the decline of kelp forests and loss of critical ecosystem function throughout Central California sanctuaries (Greater Farallones and Monterey Bay national marine sanctuaries).

Sanctuary staff are reaching out to other agencies and to broader research and stakeholder communities to improve understanding of causes and seek solutions. Currently, partner organizations are working to restore kelp habitats on the north-central coast and in Monterey Bay by reducing urchin population density on a small scale at several targeted locations. All restoration efforts are either allowed through fishing regulations or through use of a permit.

References

Duggins, D.O., C.A Simenstad, and J.A. Estes. 1989. Magnification of Secondary Production by Kelp Detritus in Coastal Marine Ecosystems. Science 245(4914):170-173.
https://doi.org/10.1126/science.245.4914.170

Filbee-Dexter, K., and T. Wernberg. 2018. Rise of Turfs: A New Battlefront for Globally Declining Kelp Forests. BioScience 68(2):64–76. https://doi.org/10.1093/biosci/bix147

Ortega, A., N.R. Geraldi, I. Alam, A.A. Kamau, S.G. Acinas, R. Logares, J.M Gasol, R. Massana, D. Krausep-Jensen, and C.A. Duarte. 2019. Important contribution of macroalgae to oceanic carbon sequestration. Nature Geoscience 12:748–754.
https://doi.org/10.1038/s41561-019-0421-8

Schiel, D. R., and M. S. Foster. 2015. The biology and ecology of giant kelp forests. University of California Press, Berkeley, California.

Wernberg, T., K. Krumhansl, K. Filbee-Dexter, and M.F. Pedersen. 2019. Chapter 3 - Status and Trends for the World’s Kelp Forests. In: C. Sheppard (ed.), World Seas: An Environmental Evaluation (Second Edition). Volume III: Ecological Issues and Environmental Impacts. Academic Press. pp.27-78. https://doi.org/10.1016/B978-0-12-805052-1.00003-6.