Sea Otters and Kelp Lab

Sea otters eat sea urchins. Sea urchins eat kelp. Count a seafloor the way a dive team does, model a coast with and without otters, and follow the comeback of California's sea otters.

Graph

Pick a quadrat

Island

Quadrat along the transect (1 is nearest shore)

Tap each sea urchin and each kelp plant inside the white square to mark it. Count a kelp plant by its holdfast, the dark knot that holds it to the rock. Rocks do not count.

● Urchins 0● Kelp 0

Record two quadrats on this island by hand first.

Your data

Counts in each 1 m × 1 m quadrat. The same quadrat always holds the same animals and plants.

Your claim

Sea otters eat sea urchins. Which island has sea otters living around it?

On this coast

Predict first

By year 50, compared with year 0, what happens?

Urchins

Kelp

Settings

Growth rate: how fast otters would grow with no limits

Run the model

Speed

Your runs

Run it again with the same settings and you get the same numbers. The last 8 runs are kept.

Your question

Scientists still argue about what holds California's otters back. Build a question someone could test. It names one thing to change or compare, and one thing to measure.

How does

affect

where or when? (optional)

Your question (edit it, or write your own)

Follow-along slideshow · 19 slides that walk through the worksheet, question by question
Printable student worksheet (PDF) · two pages, goes with this lab
Low-write worksheet (PDF) · same questions with tick boxes, word banks and worked examples
Teacher guide: NYSSLS, SEP and CCC alignment (PDF)

These are models. Real seafloors and populations also change with storms, El Niño years, oil spills, fishing gear, other predators and prey, and luck. The models leave those out so every run gives the same answer. Tab 1: the quadrat counts are practice numbers made to show the pattern Estes and Palmisano reported (Science, 1974); they are not their raw data. Tab 2: the coast model is tuned to show the pattern, and its otter loss rate matches the roughly 25% a year Estes and others measured in the 1990s (Science, 1998). Tab 3: the dots are real U.S. Geological Survey spring counts (3-year averages; mainland to 2012, range-wide index from 2013); the 1938 dot is an estimate; the model's carrying capacity and death rates are tuned to fit the dots, not measured. Environmental Science, Chapter 5: Sea Otters Step Up, and Case Study: The Southern Sea Otter.