Algae

Leon cleans the aquarium of his goldfish Gilbert, every Sunday. But two weeks ago, his family was visiting his grandma, and this past weekend he was camping with Michael. He didn’t have time to clean the aquarium. Today Leon notices something green on the walls of Gilbert’s aquarium and castle. The green stuff Leon, is actually green algae!

Algae are living organisms, and although they are very similar to plants, they are not actually plants. They don’t have the same cell and tissue structure as plants: for example, most algae don’t have roots, stems, leaves, or flowers. But like plants, algae produce their own food. They do so by using energy from the sun to produce sugars from carbon dioxide and water, a process called photosynthesis. Algae live mostly in water, but can also live in wet soil and on moist rocks.

Green algae, like the ones in Gilbert’s aquarium, are one type of algae, and they mostly live in freshwater. Some green algae consist only of a single cell: these are single-celled algae. Others are made up of multiple cells that can grow together in large colonies: they are multicellular algae. Green algae need a lot of sunlight for photosynthesis, so they usually float around very close to, or sometimes even on the surface of the water. Red algae are another common type of algae.

Some red algae are single-celled, but most species are multicellular. They mostly live in the sea, attached to solid surfaces. Red algae have different pigments than other algae and can absorb light that reaches deeper into the water. Because of this, they can photosynthesise even at greater depths, where we can’t find many other types of algae. Brown algae are another type of algae: the largest and most complex kind!

All brown algae are multicellular. They’re usually attached to something, and they often grow several metres long! By reaching to the surface of the water, they can absorb as much sunlight as possible. What helps them float up to the surface are special air-filled sacks, or air-bladders. Kelp, a species of brown algae, grows in large colonies, the so called kelp forests.

Kelp forests are some of the most diverse ecosystems in the ocean. They provide food and shelter for lots of species of fish, seabirds, and other animals like sea lions, sea otters, and even whales! Other algae are also important sources of food for animals and people in different parts of the world. For example, nori, a type of red algae, is very rich in vitamins and proteins, and is a very popular type of food in Japan. Algae also produce more oxygen than land-plants, and help keep us and other animals alive!

But in some conditions, algae can also cause a lot of harm. Some species of algae can grow and multiply so much that they cover large surfaces of water: this is called algal bloom. Algal blooms harm the plants and animals living in the water, by reducing the amount of oxygen and light that can reach them. But don’t worry Leon, nothing bad will happen to Gilbert if there are a few algae in his aquarium... But I’ll clean it anyway!