Otters vs. Climate Change – KQED/QUEST (2014)

Presence and absence of keystone species in a biological community has significant effects. To cite a few examples: Tropical fig trees form abundant food resources for many animals in times of scarcity. Bluechub fish in Eastern North American rivers construct rock nests which form a critical spawning area for many other fish in the same habitat. Beaver activity slows down hydrology and enhances water retention capacity of the ecosystems. Increased water table invigorates vegetation. At the same time reduced sun exposure of rivers allows cold water adapted fish to thrive. Cold waters in deeper layers of beaver ponds are particularly valuable rearing habitat for fish like Coho salmon. Wolves keep herbivore populations in check and allow trees to regenerate. Starfish prey on multiple grazers and prevent one type of consumer to take over the community. Removal of a keystone species from a community leads to a drastic decline.

The keystone species concept was articulated by the ecologist Robert Paine. He built the concept based on the trophic cascade idea developed by three ecologists Nelson Hairston, Frederick Smith and Lawrence Slobodkin (HSS hypothesis) in 1960. Trophic cascade is also known as the “Green World Hypothesis.”

Sea otters are another keystone species in the Pacific coast controlling sea urchin populations. Sea urchins graze on young kelp algae and prevent establishment of mature kelp forests. Kelp forests constitute a rich habitat for many marine organisms especially when they are young and vulnerable. Kelp forests are refuge habitats for juvenile fish. Additionally, Kelp forests are extremely productive ecosystems. Kelp forests sequester (absorb and capture) CO2 from the atmosphere through photosynthesis. Human activities have been releasing a lot of CO2 into the air and most of it has been dissolved in the ocean leading to ocean acidification.

If unchecked by predators, sea urchin populations can grow into underwater herds that graze across the ocean floor preventing entire stands of kelp from regenerating. Such areas are called as “urchin barrens.”

Fortunately, sea otters keep sea urchins in check, allowing the kelp to flourish and capture CO2. When otters are present, urchins hide in crevices and snack on kelp scraps. The kelp can flourish, providing habitat for many ocean organisms. Sea otters play a small role in mitigating global climate change, but their impact points to a larger lesson: wildlife conservation can save vegetation needed to reduce CO2.

 

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