Corals on Acid

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The objective of this inquiry-based lesson is for learners to gain an understanding of how increasing ocean acidity can affect the calcification of marine organisms. During this activity, learners: (1) design an experiment to quantify the CaCO3 concentration of two invertebrate skeletal samples, one that has been soaked in normal seawater and another in a low pH solution, and (2) use critical thinking and discussion to evaluate possible explanations for the difference in the skeletal CaCO3 compositions. This lesson plan includes a post-activity demonstration, which shows how the dissolution of CO2 into the ocean lowers pH.

Quick Guide

Preparation Time:
4 to 24 hours

Learning Time:
2 to 4 hours

Estimated Materials Cost:
Over $20 per group of students

Age Range:
Ages 14 - adult

Resource Types:
Activity, Experiment/Lab Activity, Lesson/Lesson Plan


Materials List (per group of students)

  • Organism information table (Table 1)
  • Samples of cuttlefish bone, coral, and shells from crab, shrimp, clam, mussel, snail, and oyster.
  • Gloves, goggles, aprons
  • Vinegar (or dilute HCl) for instructor to prepare “low pH condition” samples
  • HCl (3 M solution)
  • Thin-stem pipettes (~ 4 ml)
  • Electronic balance (precision of ± 1 mg)
  • Mortar and pestle
  • Beakers of various sizes (50 ml, 250 ml)
  • Graduated cylinders (10 ml, 50 ml)
  • Fume hood
  • Watch glasses
  • Balloons
  • Drying paper
  • Rubber spatula
  • Stirring rod
  • Filter paper and weigh paper
  • Funnel
  • Clear plastic cups
  • Straws
  • Freshwater pH indicator solution (for aquarium) with color pH scale
  • Tap water


  • Earth and Space Science
    • Earth Structure
      • Oceans and Water
  • Life Sciences
    • Diversity of Life
      • Animals
    • Ecology
      • Ecosystems
      • Populations
      • Human Impact
  • Physical Sciences
    • Chemistry
      • Chemical Reactions
      • Acids and Bases
      • Chemistry of Life
    • States of Matter
      • Gases
    • Structure and Properties of Matter
      • Mass and Weight
  • The Nature of Science
    • Science and Society
      • Risks and Benefits
    • The Scientific Process
      • Asking Questions
      • Conducting Investigations
      • Gathering Data
      • Formulating Explanations
      • Communicating Results

Informal Categories

  • Animals
  • Nature and Environment


To use this activity, learners need to:

  • see
  • see color
  • read
  • touch

Learning styles supported:

  • Involves teamwork and communication skills
  • Involves hands-on or lab activities


Access Rights:

  • Free access


  • Boleman, Casey L. ; Gravinese, Philip M. ; Muse, Ellen N. ; Marston, Andrea E. ; Windsor, John G.


  • All rights reserved, The Oceanography Society, 2013