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New Study Reiterates Sea Otter’s Importance to Coastal Ecosystem

August 3, 2011

A new study published in the journal Science describes how important apex predators, including sea otters, are to certain ecosystems.

The study, titled “Trophic Downgrading of Planet Earth”, explains how sea otters play an important role in promoting healthy coastal kelp ecosystems by “limiting herbivorous sea urchins” (who feed on kelp) through their rapacious diet. On average, sea otters consume 25-30% of their body weight each day.

Healthy kelp forests, the study explains, then promote robust kelp forest fish populations as well as filter-feeding mussels due to increased particulate organic carbon in coastal waters. Increased fish populations as a result of the kelp forests means birds such as gulls and bald eagles will diversify their diet to include more fish and small mammals and rely less on other birds and macroinvertebrates as part of their overall diet.

The study goes on to describe how physical properties of ecosystems, including forest cover, fire management, and water clarity, can be effected by the presence or absence of apex predators. These predators were long believed to just be “ecological passengers” with little effect on the overall function of an ecosystem. Contrary to that belief, the study finds that some apex predators can have a tremendous impact on an ecosystem by inciting “trophic cascades” like the effects sea otters have on kelp ecosystems.

The authors of the study, including long-time sea otter expert Dr. James Estes, suggest that “top-down forcing” must be assessed in any conceptual overview of an ecosystem. In other words, in addition to assessing physical processes (habitat loss, pollution, etc), resource managers should also assess the abundance of apex predators when determining management plans. Furthermore, the burden of proof should shift to show that “apex predators do not exert strong cascading effects” in an ecosystem rather than trying to prove that they do have an effect as is commonly the case today. In shifting the burden of proof, resource managers will assume apex predators play a role in maintaining an ecosystem until it is proven that they do not. This will result in a more precautionary approach to resource management plans that benefit species like the sea otter.

This study only underscores what sea otter advocates have been saying all along. In addition to their visual and economic appeal, sea otters play a very important role in maintaining a healthy coastal ecosystem full of life and abundance. If we value an ocean teeming with fish and other marine life instead of an open and barren wasteland, then saving the sea otter needs to be our top priority.

Estes, et al. “Trophic Downgrading of Planet Earth” Science 15 July 2011: 333 (6040), 301- 306. [DOI:10.1126/science.1205106]

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3 Comments leave one →
  1. Debbie permalink
    August 20, 2011 6:55 am

    I’m so glad yet another study is supporting the importance of sea otters to the kelp forest habitat. All too often they are blamed unfairly for everything from overfishing to natural disasters.
    It should also be noted, that they are extremely intelligent – one of just a few species that uses tools. Sea otters actually keep a rock (carry it in the loose skin under their arm), to use as a hammer (to dislodge abalone from rocks) or a hard shelf (to bang open their clams and mussels.)
    They are also among the most outstanding of mothers, in the care, teaching, and affection they give their young. While watching an otter feeding at Monterey Bay Aquarium, I saw Joy (little 504’s surrogate mother) putting off taking food from the trainer, first urging her adopted baby to eat.

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