Tavishi adjusts her oxygen mask and dives into the sea. Soon, she tells herself, she will be gazing at the wonderful colours of a coral reef.

But when she reaches it she stares in horror: the coral is a ghostly white. That means it is very sick.

Coral reefs look like plants, but are actually made up of creatures related to jellyfish. Some of these coral polyps are rough to the touch because they have a limestone skeleton.

The polyps are usually found in groups known as colonies. When a large number of these join together a reef is formed.

Many reefs depend on tiny algaeA simple plant that grows in or on water. called zooxanthellae. These live in the colony and produce 90% of the food that allows the coral to grow.

But a rise or fall in the ocean's temperature, or an increase in its acidity, can result in the algae leaving.

When that happens, the coral turns white and is left starved and vulnerableat risk of being harmed. This is bad news for the whole ocean, since 25% of all marine species live in coral.¹ 

The US National Oceanic and Atmospheric Administration has just reported a "mass coral bleaching event", which means that every ocean containing coral is affected.

Bleaching can happen if the sea temperature rises by just 1C for a month. Unless the temperature drops back again within two months, the coral can die.

But reefs can recover, although it takes years, and scientists are trying various things to help. One is to create giant tanks in which the polyps are encouraged to spawnTo cause something new, or many new things, to grow or start suddenly.. The spawn is then planted on endangered reefs.

The good news is that some corals are more resistant to heat than others. By breeding from these, scientists can increase a reef's chances of survival.

Another extremely clever approach uses underwater speakers. Coral larvaeInsects in the next stage of development after they have emerged from eggs. A caterpillar is a larva. can be attracted to struggling reefs by sending out recordings of healthy reefs, such as fish brushing against them.

But is there still hope for nature?

Yes: Some of the ideas people are using to help it are really amazing, and they are bringing real passion to the challenge. And reefs in certain parts of the world, such as Cambodia, are doing very well.

No: Humans have already done too much damage. The oceans are growing warmer all the time and the most industrialised nations are dragging their feet when it comes to reducing carbon emissions.

Or... Nature is extraordinarily resilient, as the area around the Chernobyl nuclear disaster shows. Even if humanity destroys itself through climate change, other forms of life will survive.

Algae - A simple plant that grows in or on water.

vulnerable - at risk of being harmed

Spawn - To cause something new, or many new things, to grow or start suddenly.

Larvae - Insects in the next stage of development after they have emerged from eggs. A caterpillar is a larva.