Cambridge IGCSE Marine Science Practical Skills 5: Ecological sampling and biodiversity

Cambridge 0697 marks five ecosystem activities: random quadrats for population size and species richness, line and belt transects for distribution, shore or slope profiles, sediment particle profiles and sediment moisture content. This chapter joins those methods into one fieldwork design while preserving habitat safety and sampling validity.

Define the field question

A useful question identifies place, organisms or environmental variables and comparison: “How does limpet abundance change from lower to upper intertidal shore?” is testable. “What lives on the shore?” is too broad.

Mark a safe study boundary and divide it into coordinates. Record tide, time, weather and access conditions because they affect exposure and detection. A pilot can test quadrat size, interval and identification rules without using pilot locations as final data unless planned.

Random quadrat sampling

Use random coordinates or a random-number method to position quadrats independently within the study area. Decide before sampling how to count organisms touching boundaries, such as including top and left edges but excluding bottom and right. Use the same quadrat area and rule throughout.

Count individuals for distinct stationary organisms, or estimate percentage cover for mat-forming species such as macroalgae. Species richness is the number of species recorded, not total organism count. More randomly positioned quadrats improve representation of patchy distributions.

Estimate a population where assumptions are reasonable:

$$\text{estimated population} = \text{mean count per quadrat}\times \frac{\text{total habitat area}}{\text{quadrat area}}$$