Shore Thing

Shore Thing: line and belt transects for Cambridge IGCSE Marine Science

This free game is part of our Cambridge iGCSE Marine Science (0697) course for exams in EXAM YEARS 2027-2029.

Survey a rocky shore before the tide comes in

Shore Thing is a 3D field trip to a rocky shore in Devon. Your job is to map zonation, the pattern of different species found at different heights on the shore, using systematic sampling along a transect. It covers the Cambridge IGCSE Marine Science (0697) point on investigating the distribution of species by systematic sampling using line transects and belt transects, and contrasts it with random sampling using quadrats.

• First you lay a 20 m tape from the high-tide mark to the low-water mark, at right angles to the water's edge, so it crosses every zone by the shortest route.
• The tide is still going out, so you follow it down the shore for the line transect, then work back up from the bottom with a quadrat as the tide comes in.
• Your shore ecologist, Finn, explains each new idea the first time you need it.

Line transect: where each species lives

In a line transect you stop at regular intervals along the tape (here every 2 m) and record every organism touching the line. In the game a red marker shows the sampling point at each mark, and you tap everything that touches the tape there. Tap something that is near the tape but not touching it and a short card explains why only organisms touching the line count. At the end you see a chart of where each species was found. It is quick, but it only shows where species are, not how many there are.

Belt transect: counts and percentage cover

A belt transect samples a strip along the tape. You place a 0.5 m × 0.5 m grid quadrat at every 2 m mark: spaced out like this it is an interrupted belt transect; laid end to end it would be a continuous one. Drop the quadrat away from the mark and you learn why choosing the interesting spots biases your results. In each quadrat you:

• Count animals such as limpets, rough periwinkles and beadlet anemones by tapping each one. A dot marks each counted animal so you never count one twice, and you lift seaweed to find limpets hiding underneath.
• Follow one rule for animals on the edge of the frame: count it only if more than half of it is inside.
• Estimate percentage cover of barnacles and seaweeds by painting every square that is more than half covered. The grid has 100 squares, so each square is 1%.
• Watch out for dog whelks, which can be misidentified as periwinkles.

The incoming tide creeps up the shore, so you have to plan your time. Let it reach a quadrat and you get a gap in your data, plus the field safety rules: check tide times, start at the lower shore at low water, never work alone and never turn your back on the sea.

From your data to a kite diagram

In the last mission your own counts and cover estimates become a kite diagram. Distance along the transect runs along the bottom, and each species has its own kite: the wider the kite, the more of that species was found there. You draw the barnacle kite yourself, then read the diagram to find the species that lives highest up the shore, where limpets were most abundant and where two zones overlap. The finished diagram shows rough periwinkles high up, barnacles below them, then limpets and bladder wrack, with serrated wrack and beadlet anemones at the bottom of the shore.

Making results reliable

One transect is only a sample of the shore. The final quick check is about improving reliability: repeat the transect at other places along the shore, calculate a mean for each mark and look out for anomalous results. The recap at the end sums up line and belt transects, systematic and random sampling, sources of error (misidentification, inconsistent counting, the tide) and how to fix them. Every mistake in the game brings up a short explanation with a link to the full lesson.