Worksheet

Below Whitewash Rock: Bird Droppings, Seaweed and Tide Pools

Grade 7 life science: use tide pool nitrogen data, a seaweed tank test and a food web model to show matter cycling and energy flowing at a seabird roost.

Grade 7ScienceInteractive · Printable

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1 NGSS standard
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12 questions
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Format: Interactive · Printable
Grade: Grade 7
Subject: Science
Question types: Fill in the blank, Multiple choice, Matching, Circle the answer, Short answer

About this worksheet

What students practice

Students use field data to trace nitrogen from a seabird roost into tide pool producers and consumers.
Students explain how decomposers return matter to producers while energy enters as light and leaves as heat.

How to use

Read the passage aloud and sketch the arrows of paragraph 5 on the board before students start Section 3.

Curriculum

NGSS standard covered

MS-LS2-3

Model how matter cycles and energy flows among producers, consumers and decomposers in an ecosystem.

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Below Whitewash Rock: Bird Droppings, Seaweed and Tide Pools

Model how matter from the sea cycles through tide pools while energy flows.

Four pools on the point

Read the passage and study Table 1. Then answer the questions.

A Field Trip to Whitewash Rock

1Each spring, Ms. Yolanda Petrakis takes her seventh-grade class from Pinecrest Middle School to a marine field station on a rocky point. Just off the point stands a rock stack that the station staff call Whitewash Rock. About 50 gulls and cormorants rest on it every day, and its top is streaked white with their droppings.

2The station's biologist, Dr. Mireille Toussaint, explained that the birds feed at sea. Cormorants dive for small fish, and gulls catch fish and scraps at the surface. Each bird leaves about 20 g of droppings (dry mass) on the rock every day. The droppings are rich in nitrogen, a nutrient that living things need to build proteins. Rain and splashing waves wash some of the droppings down into the tide pools at the foot of the stack.

3The class studied four pools on the sheltered side of the point. All four are about the same size and depth and sit at the same height on the shore, so the tide covers and uncovers them at the same times. They lie at different distances from the stack. Students measured the nitrogen dissolved in each pool's water, the percent of the rock covered by seaweed, and the number of limpets, small snails with cone-shaped shells that scrape seaweed off the rock (Table 1).

4Back at the station, staff wearing gloves set up a tank test. Pieces of the pools' most common seaweed, a thin red seaweed, were weighed and placed in six tanks: two with water from Pool 1, two with water from Pool 4, and two with water from Pool 4 plus 1 g of dried droppings from the rock. All tanks had the same light and temperature. After 7 days, the class weighed the seaweed again (Table 2).

5Dr. Toussaint also described other living things in the pools. Shore crabs eat limpets and other snails. When seaweed, limpets or crabs die, bacteria and other decomposers break down their remains, along with the animals' wastes, and release nitrogen back into the water. Out at sea, the small fish that the birds eat feed on tiny drifting animals, which feed on drifting algae that use sunlight to make their food.

Table 1. Four Tide Pools on the Point
Pool	Distance from stack (m)	Nitrogen (mg/L)	Seaweed cover (%)	Limpets per m²
1	2	1.6	80	60
2	10	0.8	55	40
3	40	0.2	30	22
4	80	0.1	25	20

The water in Pool 1 held how many times as much nitrogen as the water in Pool 4? times as much

Which explanation of the nitrogen and seaweed data in Table 1 fits the passage best?

A. Droppings wash into the nearest pools, and seaweed there uses the added nitrogen to grow.
B. Pools near the stack are deeper, so they hold more water and more dissolved nitrogen.
C. The limpets near the stack eat the seaweed, and that makes the seaweed spread faster.
D. Pools near the stack get more sunlight, and the seaweed there turns the light into nitrogen.

Pool 1 had 60 limpets per m², but Pool 4 had only 20. Which explanation fits the passage and Table 1 best?

A. Pool 1 had more seaweed for the limpets to scrape up, so it could feed more limpets.
B. Waves hit Pool 4 much harder, so most limpets there were washed off the rock.
C. Water with more nitrogen holds more oxygen, so the limpets crowd into Pool 1.
D. The birds carry limpets in from the sea and drop most of them into Pool 1.

The tank test

Use paragraph 4 and Table 2 to answer the questions.

Table 2. Seaweed Tank Test (average of 2 tanks; same light and temperature)
Tanks	Water used	Seaweed at start (g)	Seaweed after 7 days (g)
A	Pool 1 water	5	7.4
B	Pool 4 water	5	5.6
C	Pool 4 water + 1 g dried droppings	5	7.2

How many grams did the seaweed in Tanks A gain in 7 days? Do not round. g

The seaweed in Tanks A gained how many times as much mass as the seaweed in Tanks B? times as much

Circle the two results that, together, best show that matter from the droppings made the seaweed grow faster.

Seaweed in Pool 4 water alone gained only 0.6 g.The seaweed in each group of tanks started at 5 g.Seaweed in Pool 4 water with dried droppings added gained 2.2 g.Pool 1 had 60 limpets per m².The tanks were kept at the station for 7 days.

The seaweed in Tanks C gained 2.2 g, but only 1 g of droppings was added and most of it stayed in the water. Where did most of the seaweed’s new mass come from?

A. From nitrogen in the water, which makes up most of its mass
B. From the droppings, which the seaweed took in whole as its food
C. From the light, which the seaweed turned straight into new matter
D. From carbon dioxide and water, built into sugar using light energy

Modeling matter and energy at the rock

Use paragraphs 2 and 5 and everything on this sheet.

Use paragraph 2.

About how many kilograms of droppings (dry mass) do the birds leave on Whitewash Rock in one week? kg

Match each living thing to the part it plays in moving nitrogen around this ecosystem.

A cormorant
The red seaweed
A limpet
Bacteria on a dead crab

A. Brings nitrogen from fish caught at sea onto the rock
B. Breaks down remains and returns nitrogen to the pool water
C. Eats seaweed and builds its nitrogen into its own body
D. Takes in nitrogen from the water and builds it into new tissue

10.

Which statement about energy in this ecosystem do the passage and the tank test support best?

A. Decomposers make new energy as they break down remains and pass it back to the seaweed.
B. The droppings bring nitrogen the seaweed can reuse, but the seaweed still needs light for energy.
C. Energy cycles from the seaweed to the limpets to the crabs and then back to the seaweed.
D. The droppings hold so much energy that the seaweed in Tanks C could grow without any light.

11.

Suppose boats start landing on Whitewash Rock, and the birds stop resting there for several years. Which prediction fits the model and Table 1 best?

A. Pool 1 keeps the same nitrogen, because decomposers make all the nitrogen the pools need.
B. Pool 1 gains nitrogen, because the birds no longer take fish out of the water nearby.
C. Pool 1 has less nitrogen, less seaweed and likely fewer limpets, more like Pool 4.
D. Pool 4 gains seaweed and limpets, because nitrogen from Pool 1 spreads out to it.

12.

A visitor says, “The bird droppings are just waste. The tide pools would be the same without them.” Do you agree? Write a claim, use evidence from Table 1 and Table 2, and explain your reasoning about how matter cycles and energy flows in this ecosystem.