Carrie is a crab. She’s a pincey-wincey crab. She has ten legs which she uses to scuttle…sideways! Yes, that’s right. Because of the way her body is built, she can only shuffle forward very slowly. So she prefers to move in the direction nature intended. She has to be careful though. Her two little eyes on stalks aren’t very good at seeing things which are stationary, like rocks. So sometimes she bumps into them! Carrie has two big pincer claws on her front legs, which she uses to catch her food and eat it.

Carrie lives in a big group of crabs called a cast. They live in the coastal waters at the edge of a very large ocean. Carrie loves floating in the salty sea, letting her legs spread far and wide. As she has so many legs, she’s pretty good at sports. She can swim really fast. And she loves having running races with her friends and family over the rocks on the seashore.

One summer’s day, Carrie is floating on her back in the water beside the beach. The water feels warmer than usual. And Carrie realises that she can’t see the sun through the ocean surface anymore. There’s a lot of blue green algae all over the top of the water. In fact, the same blue green algae is stuck to the seagrass swaying on the seabed. As Carrie wonders where this has come from, she sees her cousin, Charlie, swimming towards her.

“Hey Charlie!” says Carrie.

“Hi Carrie! What are you up to?” asks Charlie.

“I’m just wondering what all of this blueish-green stuff is,” Carrie explains. “It wasn’t here before.”

“Oh, that’s algal bloom,” replies Charlie. “My dad told me about it. It’s like a really big mass of algae, and it gets much worse in the summer heat. Dad says we have to be careful not to eat it as it can poison us.”

“But we always eat algae,” Carrie points out.

“I know,” agrees Charlie. “But this kind has toxins in which really hurts crabs.”

“Where is it coming from?” asks Carrie, who is now very concerned.

“My Dad says it’s started to grow because of the fertilizers they’re using in the fields nearby, to help crops grow better. The nutrients in them, especially nitrogen and phosphorous, get down into the soil. Some of them leach down into the water under the ground. Eventually, that water flows down into the sea. Just like in the fields, these extra nutrients support the growth of lots of algae.”

“That’s awful!” states Carries.

“I know, agrees Charlie. “And the more of the toxic algae there is, the more it blocks out sunlight and reduces oxygen in the water too. That can mean fish and other organisms can’t breathe.”

Carrie thinks about all her aquatic friends in the sea. She doesn’t want the algae to harm them.

“We need to get rid of it,” she says.

“I know,” says Charlie. “But if we can’t eat it, then how are we going to do that?”

Carrie treads water for a second so she can have a think. She moves her big pincer claws from side to side keep her afloat. As she looks at them, a thought pops into her head. Of course!

“Charlie, can you get the rest of the cast together?” she asks. “I think I know how we can remove the algal bloom.”

“Sure!” replies Charlie, and he swims off to find their family and friends.

Within a few minutes, he returns with a huge group of crabs, from tiny baby ones to large grandparent ones. They gather around Carrie.

“If we all use our pincer claws,” she starts to explain, “we can pull bits of the algal bloom out of the water, on to land. If we take it far enough up the beach then the tide won’t wash it back down here again.

The eyes of the other crabs all open wide on the end of their stalks. They’re surprised at just how simple Carrie’s solution is. Within a few moments, they all make their way up to the surface of the ocean. They each grab a little bit of the toxic algae in their pincer claws and swim to the shore. Then they scuttle sideways up the sand, dragging the algae with them. Once it is safely above the tide line, they turn around and repeat the process. Before long, the only blue-ish green colour that can be seen is that of the ocean water.

The crabs all gather together at the edge of the water. They admire the sparkle of the sea, as the sun reflects off it once again. One crab starts to clap his pincer claws together. And then another. And before long there is a huge round of applause. CLAP-CLAP-CLAP! They are all so happy that they have been able to help remove the toxic algae.

“Thanks Carrie!” shouts over Charlie. “Now we know how we can help curb nutrient pollution in the future.”

“No problem,” Carrie calls back. “What about a swimming race now that the water’s clear?”

“Great,” Charlie says, enthusiastically. “What stroke?”

“Front claw?” suggests Carrie, with a cheeky grin.

Questions for discussion

What other things, apart from fertilizers, cause nutrient pollution?

Which kinds of wildlife does nutrient pollution affect?

Can you find out other ways that we can help to reduce nutrient pollution?