I walked up to the renowned three-story display of the kelp forest in the Monterey Bay Aquarium and stared. Despite the crowds and clatter of people around me, this beautiful floating forest with a diverse array of fish darting through the swaying stalks and leaves was mesmerizing. At the front of the crowd, an employee of the aquarium stood describing how kelp forests provide nursery grounds and habitat to a large number of fish species.
Pictures of a kelp forest. Source
Being a native to the east coast, I had never before had the opportunity to see a kelp forest. As I stood watching the display, I could hear my undergraduate ecology professor in my head describing how kelp forests held one of the most common examples of a key stone species, the sea otter, and top-down control of an ecosystem. I also remembered that kelp are the fastest growing plant in the world (20in/day); nearly double the growth rate of bamboo.
Ecological interactions connect an array of species at a range of spatial scales and include biological processes such as predation, competition, mutualism, and physicochemical processes such as influencing water temperatures, nutrients levels, and pollution affects.
For example, the number of people impacted by malaria near freshwater systems has been linked with the population of predatory fishes because these predators prey on smaller fish that eat mosquito larvae. On an even broader scale, the absence of top predatory fishes can alter phytoplankton density, affecting the rate of primary production and uptake of carbon dioxide, changing the carbon flux between lakes and the atmosphere.
The authors call this phenomemon of removing large apex predators and the resultant cascading affects on our ecosystems trophic downgrading. The difficulty with identifying a system with top-down control (and the potential for trophic cascades) is that the affects are often not seen until after the apex predator has been removed, at which point our ability to restore top-down control is very limited if not lost entirely.
The authors of this article also provide numerous examples of how worldwide trophic downgrading has altered and is still changing human and wildlife diseases, carbon sequestration, invasive species, and biogeochemical cycles. A serious problem considering scientists suggest we are currently in the early to mid-stages of the sixth mass extinction of our planet; a mass extinction largely caused by humans.
Leave a comment about your own experience with trophic downgrading below.
Also be sure to read about how we are giving away a free fishing rod and reel!
Estes JA, et al. 2011. Trophic downgrading of planet earth. Science. 333:301-306.
Raup DM, Sepkoski Jr. JJ. 1982. Mass extinctions in the marine fossil record. Science 215:1501.
Ray J, Redford KH, Steneck R, Berger J, Eds. 2005. Large Carnivores and the Conservation of Biodiversity, Island, Washington, DC.
Wake DB, Vredenburg VT. 2008. Are we in the midst of the sixth mass extinction? A view from the world of amphibians. PNAS. 105:11466.