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An Ecological Tipping Point
A case study: Kelp Forests
The sea otter (Enhydra lutris) is a keystone species in
the kelp forests of western California.
Removal of sea otters caused a population boom of the
purple sea urchin (Strongylocentrotus polyacanhus)
resulting in the decline of the highly productive kelp
forest ecosystem.
Macrocystis pyrifera
The kelp forest ecosystem
Nereocystis leutkeana
Kyle McBurnie
The sea otter (Enhydra lutris) as a keystone species
• Population - dramatically reduced due to hunting
for their dense fur
• The otters live, feed, rest and reproduce
within the kelp forests, and rarely
need to come to shore.
• When the otters population
declined due to predation from
Orca whales, this set in motion
a trophic cascade.
Urchin barrens
• With the reduction of otter
numbers the population of
urchins exploded.
• Sea urchins
Strongylocentrotus sp. are
capable of deforesting kelp
forests at a rate of 30 feet
per month.
Impacts & Consequences
for
biodiversity & ecosystems
services
Before:
• Kelp forests are similar to rain
forests in that they also absorb &
store C02 from the atmosphere.
• The huge range of forest
biodiversity acts as a focal point
for eco-tourism, with the forests
gone this income is lost.
After:
References/Images:
Seals/surface & otters2: The Alaska Wildlife Alliance, Anchorage, AK 99520-2022 ,Sea Otters and Kelp Forests, Available at:
http://akwildlife.org/wp-content/uploads/2013/02/sea_otters_and_kelp_forests_11-5.pdf
Seal/Forest: Rosenstiel School of Marine & Atmospheric Science, Miami, Fl, USA. Underwater Photography 2013 Winner, Kyle
McBurnie, California, Harbor seal (Phoca vitulina) in a kelp forest at Cortes bank, near San Diego, CA. Available at:
http://www.rsmas.miami.edu/outreach/underwater-photography/2013-winners/
Kelp/fish: National Marine Sanctuaries, Kelp Forests - a Description. Available at:
http://sanctuaries.noaa.gov/visit/ecosystems/kelpdesc.html
Otter eating: Biodiversity of the Central Coast, Sea otter (Enhydra lutra). Photos by Keith Holmes, Hakai Insitute Available at:
http://www.centralcoastbiodiversity.org/sea-otter-bull-enhydra-lutris.html
Otter collecting: Arkive.org, Sea otter collecting sea urchin photo by Jeff Foot. Available at: http://www.arkive.org/seaotter/enhydra-lutris/image-G24397.html
Urchin barren, Urchin cover: California Department of Fish and Wildlife, “Perfect Storm” Decimates Northern California
Kelp Forests, Photos by A. Maguire & A. Weltz Available at: https://cdfwmarine.wordpress.com/2016/03/30/perfect-stormdecimates-kelp/
Consequences before & after: Natural History Photography Blog, The Disappearing Kelp Forests of San Clemente, Photos by
Phillip Cotta. Available at: http://www.oceanlight.com/log/category/photography/aerial-photography
Narration by Stephen Gill