Zostera novazelandica facts for kids

Zostera novazelandica is a type of seagrass found along the coasts of New Zealand. It's also known by its Māori names like karepō, nana, rehia, and rimurehia. Some scientists think it's a unique species. Others believe it's the same as another seagrass called Zostera muelleri.

What Does This Seagrass Look Like?

Zostera novazelandica is a marine flowering plant. This means it's a plant that lives in the ocean and produces flowers. It has long, thin leaves that look like blades of grass. These leaves can grow up to 50 centimeters (about 20 inches) long. They are usually olive-green and have three lines running down them.

Under the water, this seagrass has a special root system called a rhizome. This rhizome grows sideways, helping the plant spread and stay firmly in the sand or mud.

Flowers and Seeds

The flowers of Zostera novazelandica are small and hard to see. They are hidden among the leaves. Each plant has both male and female flowers. These flowers are packed tightly together.

After flowering, the plant produces small, oval-shaped fruits. These fruits are smooth and yellow, about 2.5 millimeters long. Inside, they hold tiny brown seeds, which are about 2 millimeters long.

Where Does This Seagrass Live?

Seagrasses are special plants that have learned to live in the ocean. They are often found along coastlines around the world. The Zostera group of seagrasses lives in places like Australia, Southeast Asia, and even northern countries.

Its Home in New Zealand

For a long time, people thought New Zealand had two types of seagrass. One was Zostera capricorni, also found in Australia. The other was Zostera novazelandica, which was thought to live only in New Zealand.

However, some studies now suggest that these two might actually be the same species. If this is true, then Zostera novazelandica would also be found in parts of Australia and Papua New Guinea. If they are different, then Zostera novazelandica is endemic to New Zealand. This means it naturally lives only there.

You can find this seagrass all along the New Zealand coast. It grows from the very north of the North Island down to Stewart Island in the South Island. It often forms large underwater "meadows" or smaller patches. These patches can be found in calm areas like estuaries or tidal flats.

What Kind of Habitat Does It Like?

Zostera novazelandica prefers places that are sheltered from strong waves. It likes areas where water stays trapped at low tide, like in tide pools or on reef platforms. It often grows in patches mixed in with seaweed beds.

This seagrass needs enough sunlight to grow. If it doesn't get at least 10-20% of the surface light, it can die. It doesn't like very deep water because deep water means less light and more pressure. It prefers water that is a little bit salty, known as brackish water. This is why it grows well in estuaries, where fresh river water mixes with salty ocean water. It also likes soft, muddy, or sandy seafloors.

Life Cycle of the Seagrass

Zostera novazelandica is a perennial plant. This means it usually lives for two or more years. Its life changes with the seasons.

Winter Changes

In winter, the seagrass patches shrink. They can lose about a third of their size. More patches die in winter than in other seasons. New patches start to appear from July to November. These new patches often form when bigger patches break apart.

Spring Growth

When spring arrives, the seagrass starts to grow back. New patches form from July to September. About 40% of new patches come from seeds that sprout. The other 60% come from pieces of older plants breaking off and growing. This often happens in tide pools or cracks in the rocks.

The plants start to flower in spring. You can see young flowers appearing in late October.

Summer and Autumn

In summer, more flowers appear, especially in patches higher up on the shore. Mature seeds can be found from late December to March. These seeds will then wait through winter and sprout the next spring. The plants also grow bigger by extending their rhizomes.

The seeds don't play a huge role in how the seagrass spreads each year. Most of the new growth comes from the plants themselves spreading. Once a patch reaches a certain size, it has a much better chance of surviving. The leaves are biggest in summer. The flowering season lasts about eight months, from spring to late autumn. Water movement is important for pollination in summer.

By autumn, you can still find seedlings in rock pools and tidal cracks, and some plants are still flowering. Sometimes, this seagrass can become an annual plant. This means it lives for only one year, growing in spring and dying by the end of autumn.

What Eats This Seagrass?

Zostera novazelandica makes its own food through photosynthesis. This is the process where green plants use sunlight, carbon dioxide, and water to create energy. Even if some of its leaves are damaged, the seagrass can recover. This is because a lot of its plant material is stored underground in its rhizomes. This stored energy helps it quickly grow new shoots.

This seagrass grows best in soft, muddy, or sandy seafloors. It likes soil depths between 60 and 100 millimeters. Water with lower salt levels can help the seagrass produce more flowers.

Who Are Its Predators?

The biggest threat to Zostera novazelandica is a small crab called Macrophthalmus hirtipes. This crab burrows into the seagrass patches. It eats the leaves, stems, and roots of the seagrass. The crab relies on this seagrass for 30% to 50% of its diet.

These crabs also damage the edges of the seagrass patches. Their burrowing can loosen the soil and make it harder for the seagrass roots to hold on. This can lead to the loss of soil and the shrinking of seagrass beds.

Diseases and Other Threats

The seagrass can also get a disease called "wasting disease." This disease damages the leaves. When the leaves are damaged, the patches become more open to crab attacks, which can cause more erosion. Luckily, the patches often recover well by growing new leaves.

However, the decline of New Zealand's seagrass isn't just from natural causes like crabs or diseases. Human activities also play a big part. Things like pollution from farms and cities, climate change, and fish farming can harm the seagrass. Warmer water temperatures can stress the plants, making them flower more. This uses up their stored energy.

Why Is This Seagrass Important?

Seagrasses like Zostera novazelandica are very important for the ocean.

Past Uses

In the past, Zostera species were used for different things. People used them as a food source. They were also used to make paper or to stuff mattresses. For the Māori people, New Zealand seagrass was important for preparing food and decorating clothes.

Historical Records

It's believed that in the 1800s, there were huge meadows of Zostera novazelandica. Early European explorers wrote about how common it was. One naturalist, Leonard Cockayne, said the seagrass "covers the muddy floor…for many square yards at a time."

Importance for the Ocean

When seagrass beds shrink, it can affect other animals. For example, fewer black swans and less fish have been caught when seagrass declines. Seagrasses are like the base of the food web in their areas. They use sunlight to create food, which then feeds many other creatures.

They also help keep the seabed stable. This means they stop the sand and mud from washing away. They create a safe home for many different kinds of ocean life. Many young fish use seagrass beds as nurseries. They grow up there during their early months. For example, the New Zealand snapper, an important fish for fishing, uses seagrass like Zostera novazelandica as a nursery for its first year of life.

Need for More Research

We still don't know a lot about Zostera novazelandica. Only a few people have studied it in detail. Recently, researchers have found that this seagrass is quite good at recovering from disturbances. This information is very helpful for managing and protecting it from human impacts.