Study
Sea otters: their role in structuring nearshore communities
Estes, James A.; Palmisano, John F.
Science, 1974
Nearshore communities were surveyed by diving at Aleutian islands where sea otters had recovered after the fur trade and at islands where they had not, comparing sea urchin abundance and size and the extent of kelp.
- Studied in
- Enhydra lutris, Strongylocentrotus, Macrocystis
- Sample size
- islands with and without otter populations, surveyed by diving
Islands with otters had few and small urchins and extensive kelp. Islands without otters had abundant large urchins and little kelp.
What it means
The authors' reading, and ours. Where they differ, that difference is the point.
How the authors put it
Sea otter predation on urchins limits grazing pressure on kelp, so the presence or absence of otters restructures the nearshore community.
How NatureHQ reads it
A natural experiment produced by history: otters were hunted to near-extinction and recovered patchily, leaving islands with and without them in the same region. That is far stronger than an ordinary correlation and weaker than a manipulation — the islands were not assigned, and they differ in other ways. Later work found the pattern varies considerably by region, which is exactly what a natural experiment cannot rule out from a single comparison.
- Otter presence was not assigned by the researchers; islands may differ in other respects.
- Later work found substantial geographic variation in the strength of the effect, and other drivers of urchin abundance operate.
What this study is used for on NatureHQ
One study can inform several subjects. Here is everywhere this one is cited.
Trophic cascades
Removing a predator sometimes changes vegetation two links down the chain. It is demonstrated in small manipulable systems and much harder to establish in large ones — where it is asserted most often.
Trophic cascades
Aleutian islands with sea otters had small urchins and thick kelp; islands without had large urchins and bare rock. Nobody assigned the otters — history did, by hunting them out unevenly.
Published by: American Association for the Advancement of SciencePublished in Science or Science Advances (AAAS).
doi.org/10.1126/science.185.4156.1058
Checked against Crossref on 2026-09-28, and they agree on the title, the authors and the year.
NatureHQ summarises research in its own words and does not reproduce published text. Reviewed 2026-09-04.