Undersea gardens
As we walk along the edges of the sea, we often see seaweeds growing near the shore or thrown up onto the beach by waves.
These seaweeds are part of huge undersea gardens that grow in the waters of the sea.
More than one thousand kinds of seaweeds live in the seas around New Zealand.
What are seaweed?
Seaweeds are algae that grow in the sea. They’re not plants because they don’t have flower or seeds - they have spores instead.
Some seaweeds grow only in winter and others only in summer. Some grow all year around.
Parts of a seaweed
The parts of a seaweed have special names.
Thallus is the name for the whole seaweed.
The stipe is the main steam of the seaweed.
The holdfast works like an anchor to keep the seaweed attached to rocks, reefs, shells, or other plants.
Air bladders help to hold the blades upright in the water.
The blades are the leaves of the seaweed. They take in sunlight to help the seaweeds to grow.
The fruiting bodies are tucked away in the blades. They make spores that grow in to new seaweeds.
Seaweed colours
Seaweeds fit into three groups.
Colour seaweeds- green seaweeds, brown seaweeds and some pink seaweeds.
Green seaweed often grows near fresh water. You may find them growing where streams flow into the sea. Sea lettuce is a green seaweed.
Kelps are brown seaweeds. There are lots of different sorts of kelp, and they can form forests in the sea. Red seaweed can be pink, bright red, dark red, or even purple. Agar weed is a red seaweed.
Seaweed shapes
Seaweeds come in all shapes and sizes.
They can look like grass or like spaghetti. Some look like flat sheets, and some look like tubes. They can be stuck tightly to rocks, or they can have very fine branches.
Ulva seaweed looks like lettuce.
Neptune’s necklace looks like a row of beads.
Neptune is the Roman god of the sea.
The rimu tree got its name because the maori name for seaweed is “rimu”. The fronds of young rimu trees look just like seaweed.
Seaweed sizes
Some seaweed are as tiny as your little fingernail. Others are ten times as tall as you are. Giant kelp is the largest New Zealand seaweed. It can grow to 70 metres high. The largest seaweed in the world can grow faster than any plant.
The feel of seaweeds
Some seaweed feels slimy. There slime protects the blades from damage by strong waves, sand, and rocks.
Some seaweed feel wiry, and other feels rubbery.
Dry karengo feels like cellophane.
How sea animals use seaweeds
Seaweed provides safe places for sea animals to live.
Crabs hide from their predators inside seaweeds.
Seahorses wrap their tails around seaweeds so that they don’t get swept into deep seas.
Seaweed can be food for some of these animals, too.
How people use seaweeds
Seaweed can be a healthy food for people. In New Zealand, we eat a seaweed called karengo. It’s baked in the oven and eaten with a little butter. You can also make Sushi with it.
Seaweed are used by gardeners to make soil healthy and plants strong. Farmers can feed seaweed to their animals, too. Seaweed contains slimes and gels. We can use these slimes and gels in food, medicines, shampoo, and paint.
A kind of sugar that comes from red seaweed is used in ice cream to make it creamy.
Seaweeds in history
Maori used bull kelp to make poha titi. These were waterproof bags used to store the mutton birds they hunted.
Children plucking mutton birds. The birds will be stored in a poha titi.
In the second world war, lots of New Zealand children collected agar weed. The agar in the seaweed was used to keep tinned meat fresh. The tinned meat was sent to the soldiers who were fighting in the war. The agar was also used in medicines for the soldiers.
This illustration of children collecting seaweed was published in the school journal 1942.
Finding out more
Scientists are still finding out about the secrets of our undersea gardens.
They are studying the life cycles of seaweed, and they are finding new ways that seaweeds can be useful to people.
The End
By Shreeya
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