---
title: "Coral Bleaching & Acidification"
description: "Explain the mutualistic symbiosis between coral polyps and photosynthetic zooxanthellae; describe how heat stress causes bleaching (corals expel zooxanthellae and turn white); explain ocean acidificat"
canonical: https://lightmysky.com/learn/science/coral-bleaching-and-acidification-mt_EXO1bJ3G_v
source: https://lightmysky.com/learn/science/coral-bleaching-and-acidification-mt_EXO1bJ3G_v.md
retrieved: 2026-10-19
---

> **Agent view.** This is the Markdown twin of the page, for tools and assistants.
> When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md
> API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md
> Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt
> Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json
> Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`.

# Coral Bleaching & Acidification

Explain the mutualistic symbiosis between coral polyps and photosynthetic zooxanthellae; describe how heat stress causes bleaching (corals expel zooxanthellae and turn white); explain ocean acidification chemistry: CO2 dissolves in seawater to form carbonic acid, lowering pH and dissolving calcium carbonate skeletons; connect reef loss to the collapse of habitat for ~25% of marine species; evaluate current reef restoration efforts

Subject: Science · Area: Ocean Life · Ages 12 to 13
Page: https://lightmysky.com/learn/science/coral-bleaching-and-acidification-mt_EXO1bJ3G_v

## Lesson: When Coral Turns White

A coral reef is built by tiny animals called coral polyps. Each polyp hosts thousands of algae called zooxanthellae living right inside its tissue. The algae photosynthesize and pass sugar to the coral. In return, the coral gives the algae a safe home and the carbon dioxide they need to grow. The algae's pigments are also what give healthy coral its color. The reef shelters many of the fish people catch and love to watch.

*(drawing: Ocean pH has been slowly dropping for decades. Lower numbers mean more acidic water.)*

When water stays too warm for too long, the zooxanthellae inside the coral start producing harmful byproducts. The coral responds by pushing its algae out. Without the algae's color, the clear coral tissue shows the white skeleton underneath. That is bleaching. The coral is not dead, but it is starving and much more likely to die if the heat does not ease up.

**Example.** On the Great Barrier Reef, repeated marine heatwaves have bleached huge sections of coral. Separately, extra carbon dioxide in the air is dissolving into the ocean, forming carbonic acid, and that acid makes it harder for coral to pull calcium carbonate from the water to build new skeleton. About a quarter of all marine species spend part of their life on a reef, so losing reefs means losing that habitat too.

Scientists are growing heat-tolerant coral in nurseries and transplanting it onto damaged reefs. It is real progress, but these projects still only cover a small fraction of the reefs at risk. Restoration helps, it does not yet solve the underlying heat and acidification problem.

**Recap.** Warmer, more acidic water breaks the coral-algae partnership, bleaches reefs, and threatens habitat that a quarter of ocean life depends on.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Acids, Alkalis & pH](https://lightmysky.com/learn/science/acids-alkalis-and-ph-mt_AN2kJE6I0s)
- [Coral Reefs](https://lightmysky.com/learn/science/coral-reefs-mt_AxGPeVRm__)
- [Ocean Currents and Global Heat](https://lightmysky.com/learn/science/ocean-currents-and-global-heat-mt_Mp_CpVK6e-)
- [Predator Loss and Ecosystem Effects](https://lightmysky.com/learn/science/predator-loss-and-ecosystem-effects-mt_NPTjGJIyb3)
- [Ocean Ecosystems](https://lightmysky.com/learn/science/ocean-ecosystems-mt_w4OYcWJs6H)

## Opens up

- [Seawater Chemistry: the Carbonate System and pH](https://lightmysky.com/learn/science/seawater-chemistry-the-carbonate-system-and-ph-mt_BrdrNZmBzE)