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Otters, Urchins and a Heat Wave: Arguing About a Kelp Forest

Grade 7 life science: use a zoo's sea otter release records and kelp cove dive surveys to argue how otters and a heat wave changed populations.

Grade 7ScienceInteractive · Printable

Aligned toMS-LS2-4

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Single worksheet
Auto-graded online
1 NGSS standard
Printable answer key
11 questions
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Details

Format: Interactive · Printable
Grade: Grade 7
Subject: Science
Question types: Fill in the blank, Multiple choice, Matching, Short answer

About this worksheet

What students practice

Students use survey data to argue that a change in a living part of an ecosystem affected other populations.
Students use data to separate the effect of a physical change from the effect of a living change.

How to use

Read the passage, then have students trace one column of Table 1 at a time before they compare years; the heat wave year is the key contrast.

Curriculum

NGSS standard covered

MS-LS2-4

Argue from evidence that changes to physical or living parts of an ecosystem affect its populations.

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Otters, Urchins and a Heat Wave: Arguing About a Kelp Forest

Use six years of dive surveys to argue how living and physical changes affected kelp forest populations.

Otters return to the cove

Read the passage and Table 1, then answer the questions.

The Kelp Cove Surveys

1Harborview Zoo runs a sea otter program. Young otters found stranded on beaches are raised at the zoo by adult otters that cannot be released, so the pups learn to dive, find food and groom their thick fur. When they are ready, the zoo releases them at Kelp Cove, a rocky bay where sea otters had been missing for many years. Each released otter wears a small tag, so the zoo can tell its otters from wild ones that swim in from other bays. This summer, seventh grader Tomasz Nowak joined the zoo's teen program and helped biologist Kaimana Akana review six years of dive surveys from the cove.

2Kelp is a large brown seaweed that grows from the rocky bottom toward the surface, forming underwater forests. It usually grows best in cool water that is rich in nutrients, and long stretches of unusually warm water can weaken it. Sea urchins are spiny animals that crawl over the rocks and graze on kelp, sometimes chewing through the base so the whole plant drifts away. Sea otters eat many kinds of animals from the sea floor, including crabs, clams and a lot of sea urchins. Many kinds of young fish, such as rockfish, hide among the kelp from larger fish.

3The zoo began releasing otters in 2018 and released a few more each year until 2021. Each August, divers counted the otters in the cove from a boat, counted urchins and kelp plants inside marked squares on the bottom, and counted young rockfish along the same underwater path. The same marked squares were checked every year. A logger on the bottom recorded the water temperature. Kaimana reminded Tomasz that a survey shows what changed and when, so a strong argument has to match the timing of each change. In the summer of 2022, a marine heat wave, a long stretch of unusually warm ocean water, spread along the coast.