Ocean plants
Life on Earth wouldn’t be possible without these oxygen-producers
PLANTS are essential for life on Earth. They provide humans and animals with food, shelter and medicine. The basic food for all organisms comes from plants and the process by which they convert the sun’s energy into nutrients is called photosynthesis, which uses chlorophyll – the pigment that makes plants green. Plants also use carbon dioxide for photosynthesis and release oxygen as a by-product. Without oxygen, animals and humans couldn’t breathe. For their part, most plants need sunlight, air, water, nutrients and space to survive.
All life on Earth is concentrated in the biosphere. This a relatively thin layer around the planet’s surface that supports all living things. The biosphere is made up of the lithosphere (soil and rocks), hydrosphere (water) and atmosphere (gases).
The hydrosphere includes all aquatic life on Earth, both seawater and freshwater. The word aquatic is defined as anything relating to water, while the word marine is used to refer to anything to do with saltwater, in other words the world’s oceans. There are three main types of marine biome, namely the open ocean, coral reefs and estuaries.
All living things are adapted to their natural environment or habitat, which means their natural habitat contains everything the organism needs to thrive. Much of the life on our planet – including plants – is found in the ocean. But how do plants survive underwater, given their need for light, air and nutrients, as well as enough space to grow? And especially in saltwater? Let’s find out.
OCEANS AS A HABITAT FOR PLANTS
Scientists estimate 50-80% of the oxygen produced on the planet comes from marine plants. But in the ocean, which covers about 71% of Earth’s surface, access to light and air for marine plants – which also photosynthesise – is a little challenging. But marine plants, of which there are thousands of species, are well-adapted to withstand the high levels of salt in the water and to optimally harness the reduced levels of sunlight beneath the water. They play a crucial role in the production of oxygen, function as habitats, protect certain marine animals from predators and serve as a source of food. But they’re sensitive to the water’s temperature, which means they’re threatened by global warming.
TYPES OF MARINE PLANTS
Though there are thousands of marine plant species, all of them can be grouped into two categories: floating or rooted. Floating plants float in the water near the surface, while rooted marine plants ensure
they have access to sunlight by growing in shallower water near the coast. The upper ocean layer that receives the most sunlight is called the epipelagic zone.
S Algae and seaweed Algae are a large variety of species of organisms that photosynthesise and live in water – from tiny microscopic plants to enormous ones of up to 50m tall that grow in underwater forests. Larger and more complex algae are commonly known as seaweed. There are about 11 000 seaweed species.
Algae grows on rocks, in estuaries and on reefs and can be roughly divided into three
groups: red, brown and green. They all contain chlorophyll but red and brown algae also have other pigments that help them absorb sunlight. Seaweed is a popular and healthy food
ingredient in Asian countries such as Japan, China and Korea. It’s found in sushi, salads, soups, smoothies and even stews.
S Kelp is a type of seaweed of which there are around 30 species found worldwide. It’s considered the largest marine plant and is also the
fastest growing. Some types of kelp can grow to more than 50m tall and grow about 30cm a day – but in ideal conditions these species can grow as much as 60cm in a single day!
Kelp is part of the group of brown algae. It prefers cooler coastal areas and is rich in minerals and trace elements. It grows at depths of between 6 and 20m but in clear water can grow even as deep as 80m.
Kelp grows in underwater forests and not only does it provide shelter for marine creature, it’s also used for commercial purposes to make a wide variety of products such as toothpaste, shampoo, salad dressing, pudding, cake, frozen foods and pharmaceutical and cosmetic products.
S Phytoplankton These microscopic, single-cell algae might rightly be called the “superstars of the ocean”. Along with zooplankton (tiny marine animals), they form a group of tiny drifting organisms found in the epipelagic zone. Phytoplankton form the basis of the ocean food chain as they’re eaten by zooplankton, crabs, shrimp and mussels, which are in turn eaten by larger marine animals, fish and birds. Phytoplankton are extremely sensitive to any changes in their environment, including water temperature, acidity and salt levels.
S Seagrasses These are the only marine flowering plants (with leaves, roots, flowers and seeds). They lived on land millions of years ago and evolved into aquatic plants. Seagrasses grow in clumps and form grass “meadows” (resembling fields on land) on the ocean floor, anchoring themselves with thick root systems. There are about 60 species.
Seagrasses need lots of light and this dictates at which depths they’re found. Seagrass meadows are an important habitat for a variety of marine life, including sea turtles, crabs and crayfish. These plants filter impurities from water and soil, ensuring the water is clear and healthy. Like algae, seagrass is also an oxygen producer and serves as food for a variety of marine animals and fish. Seagrass meadows can be large enough to spot from space!
S Mangrove forests The trees that make up these forests are marine plants. They live in tropical climates, are usually found near or in seawater and are uniquely adapted to filter saltwater. Their leaves can discharge excess salt, which enables the mangrove to survive where other land plants can’t.
Mangrove forests have complex root systems that help to combat erosion by binding the soil. The forests offer shelter to a variety of birds, fish and other marine life. Mangroves remove up to 10 times more carbon dioxide from the atmosphere than rainforests.
CORAL REEFS
These aren’t plants but rather ecosystems made up of coral polyps (tiny marine animals) that live in symbiosis with algae. Aquatic plants such as seagrass, mangrove forests and a group of microscopic marine life called zooxanthellae (single-celled dinoflagellates) are found in the warm, shallow waters surrounding coral reefs.
Less than 20% of our planet’s oceans have been discovered, studied and documented. So who knows what other types of fascinating plants might be lurking in the dark depths of our seas, waiting to be discovered by future generations?