Tide-Pool Survey: How Much Data?

Identify what was observed and report the number of observations.

Read the Field Records

A quadrat is a square frame used to mark a sampling area. Unless stated otherwise, each surveyed quadrat contributes one observation.

During a marine biology field trip, students count sea stars in 7 quadrats. They find 21 sea stars altogether. The data set lists the sea-star count for each quadrat. How many observations does it contain?

A. 21 observationsB. 7 observationsC. 28 observationsD. 3 observations

The team records three species in each quadrat. Consider only the data set of limpet counts.

Species Counts by Quadrat
Species	North	East	South	West
Limpets	8	5	8	3
Shore crabs	2	1	0	2
Sea anemones	4	6	3	4

How many limpet-count observations are shown? observations

A field notebook contains one completed species-count record for each quadrat labeled Q11 through Q18, including both Q11 and Q18. There are no skipped labels. How many observations are recorded?

A. 8 observationsB. 29 observationsC. 18 observationsD. 7 observations

Students record how many different species they find in each quadrat. The notebook separates the records by shoreline section.

Species per Quadrat
Section	Recorded species counts
Outer pools	4, 6, 4, 5
Middle pools	7, 5, 6
Inner pools	3, 4, 3

How many quadrat observations are recorded across all three sections? observations

Count Observations in Summaries

Use the frequencies, not the measured species counts, to find how many observations a display represents.

This histogram groups quadrats by the number of snails found. Each quadrat appears in exactly one bar. Intervals include their lower endpoint but not their upper endpoint.

How many snail-count observations does the histogram represent? observations

The table summarizes how many different species were found in each quadrat.

Species Richness Survey
Species found	Number of quadrats
2	3
3	6
4	8
5	5
6	2

How many observations are in this data set? observations

Two teams summarize their sea-anemone counts. Each quadrat was surveyed by only one team.

Team Frequency Summaries
Anemones per quadrat	Reef team quadrats	Cove team quadrats
0	2	5
1	5	4
2	6	3
3	3	4

Which statement correctly compares the numbers of observations?

A. The Reef team has 6 observations; the Cove team has 5.B. The Reef team has 3 observations; the Cove team has 3.C. The Reef team has 16 observations; the Cove team has 16.D. The Reef team has 4 observations; the Cove team has 4.

A report includes only this box plot of limpet counts per quadrat. No sample size is listed.What can you conclude about the exact number of observations?

A. It is 6 because the median limpet count is 6.B. It is 5 because the plot marks five summary values.C. It is 13 because the largest limpet count is 13.D. It cannot be determined from this box plot alone.

Check the Final Report

Decide exactly which records belong in each requested data set. Explain your reasoning on the final question.

The class has complete crab counts from 12 quadrats. For a close-up study, the report uses only quadrats where at least 2 crabs were found.

Crab Survey Summary
Crabs per quadrat	Number of quadrats
0	2
1	3
2	4
3	2
4	1

How many observations belong in the close-up study's data set? observations

10.

Each completed quadrat provides one species-count observation. The final field-trip report includes both natural habitats but excludes the practice tank.

Completed Survey Records
Location	Completed quadrats
Rocky tide pools	8
Sandy tide pools	6
Practice tank	5

How many observations should the final field-trip report include? observations

11.

Nia has 28 species-count observations, one from each of 28 quadrats. She organizes all of them into a frequency table with 6 rows. No records are removed or added. How many observations does the table represent?

A. 28 observationsB. 34 observationsC. 22 observationsD. 6 observations

12.

Students find 43 mussels across several quadrats. They measure the shell length of every mussel and record one length per mussel. This new data set contains individual shell lengths, not mussel counts per quadrat.

How many shell-length observations are in the new data set? observations

13.

At a final survey stop, four groups each survey 3 different quadrats. No quadrat is surveyed by more than one group. Each group then submits just one number: its total sea-star count across its 3 quadrats. The class data set contains only those submitted group totals. Ezra says this data set has 12 observations. Is he correct? Report the number of observations and explain what each observation represents.