Coral Bleaching & Acidification

Activities to try

1. 1

   Drive the reef: two levers, two different failures

   Why it works: Bleaching is a reversible-until-it-isn't stress response driven by heat, while acidification is a chemical attack on the skeleton driven by CO2; they are two distinct threats from the same emissions, and only cutting CO2 addresses both.

   1. Work with a reef model that has two separate controls: water temperature and atmospheric/dissolved CO2.
   2. Raise the TEMPERATURE and describe what happens: zooxanthellae drain out of the polyps, the coral turns white, and a coral food/energy meter falls.
   3. Hold the heat high and observe the coral die; then, in a fresh run, ease the heat back quickly and watch colour return — state in your own words why duration matters, not just peak temperature.
   4. Separately raise the CO2 and describe the different failure: a pH readout falls, carbonate-ion tokens the coral needs to build its skeleton become scarce, growth stalls, and skeleton edges pit and dissolve.
   5. Watch a linked species panel: reef-dependent fish and invertebrates thin out as the reef structure is lost (~25% of marine species).
2. 2

   Inside the polyp: anatomy and the two mechanisms

   Why it works: The coral is an animal in mutualism with photosynthetic algae; losing those algae starves it and reveals the white skeleton through its still-living tissue (bleaching), while a separate chemistry chain (CO2→carbonic acid→↓pH→↓carbonate) physically weakens its skeleton (acidification).

   1. Examine a cutaway of a coral polyp and identify the zooxanthellae living inside its tissue; state in your own words that these algae give the coral its colour AND most of its food.
   2. Compare three states side by side — a healthy coloured polyp, a bleached polyp (still a live animal whose transparent tissue reveals the white skeleton beneath after the algae are expelled), and a coral whose skeleton is pitted/dissolving from acidification — and say which threat produced each.
   3. Follow a labelled chemistry chain and fill in the missing steps: CO2 + H2O → carbonic acid (H2CO3) → lower pH → fewer carbonate ions → harder to build/maintain the CaCO3 skeleton.
   4. Write a one-sentence contrast: how the thermal mechanism differs from the chemical mechanism.
3. 3

   Does acid attack something hard? Predict–Observe–Explain

   Why it works: Hard calcium-carbonate structures are not safe from acids; a mildly more acidic ocean is enough to reduce carbonate availability and attack skeletons over time.

   1. Before observing, write a prediction with a reason: could a weak acid damage something as hard as a seashell or coral skeleton? Most people expect 'no, it's too hard'.
   2. Observe a clean shell or a piece of natural chalk or limestone (calcium carbonate) placed in vinegar; note the immediate fizzing (carbon dioxide gas being released) as the surface is attacked and slowly dissolves. Note: many blackboard chalks are calcium sulfate and will not fizz, so check the material first.
   3. Explain the link to ocean acidification: CO2 makes seawater more acidic, attacking the same calcium carbonate that corals and shellfish build.
   4. State the important caveat in your own words: vinegar is far stronger than seawater, so the ocean effect is much slower and gentler. The shared chemistry is that acid reacts with carbonate, but in the ocean this mainly lowers the number of carbonate ions, making skeletons harder to build and easier to wear away, rather than visibly fizzing them away. Seawater stays slightly alkaline and becomes LESS alkaline, not an actual acid.