Seagrass

Seagrasses are special flowering plants that grow in the ocean. Unlike seaweed or beachgrass, they are true plants with flowers. There are about 60 different kinds of seagrasses.

These plants have long, narrow leaves that spread out in large underwater areas called meadows. They look a bit like grass on land. Seagrasses live in shallow coastal waters where sunlight can reach them. They are anchored in sandy or muddy bottoms. Like other plants, seagrasses make their own food using sunlight through a process called photosynthesis.

Seagrass meadows are very important for the ocean. They help store carbon, which helps fight climate change. They also provide homes and food for many sea animals. These meadows are some of the most productive places in the ocean, supporting life in ways similar to coral reefs.

Overview

Seagrasses are special plants that grow in the sea. They came from land plants that returned to the ocean millions of years ago. They can only live where the water meets the land or in the ocean. Their pollination and seed making all happen underwater. Their leaves are made for capturing sunlight.

These plants help keep coastal areas healthy. They give food and shelter to many sea animals. Sadly, many seagrass areas are disappearing. This can hurt sea life and people who depend on the ocean. Protecting these plants is important for keeping the sea healthy.

Evolution

Seagrasses are special flowering plants that grow in the ocean. They came from land plants that moved back into the sea a very long time ago. These plants are part of a group called monocots, which includes grasses and similar plants.

Unlike other sea plants, such as salt marsh plants or mangroves, seagrasses all come from the same plant family. Even though there aren't many kinds of seagrasses, they grow in shallow water on every continent except Antarctica. Scientists study their genes to learn how they changed to live in the ocean. This helps us understand how plants adapt to new places.

Taxonomy

Seagrasses are special flowering plants that grow in the ocean. There are about 60 different kinds of seagrasses. They belong to five families: Zosteraceae, Hydrocharitaceae, Posidoniaceae, Cymodoceaceae, and Ruppiaceae. All of these families are part of a group called Alismatales.

The plant group called Ruppia grows in slightly salty water. Some scientists do not think it is a true seagrass. How scientists group these plants can change depending on the system they use.

Cell walls

Seagrass cell walls are similar to those of land plants, like having cellulose. Some seagrass cell walls have special kinds of polysaccharides, more common in sea algae such as red, brown, and green algae.

Besides polysaccharides, seagrass cell walls include important proteins. These proteins help build the cell wall and control processes inside cells. These proteins were first studied in seagrass in 2020 and show unique features that might help seagrass manage water balance.

Seagrass cell walls also contain lignin, which makes walls stronger, though usually less than in land plants. Learning about these cell wall parts can be useful for making paper or insulating materials.

Sexual recruitment

See also: Seagrass meadow § Using propagules, and Seagrass meadow § Movement ecology

Seagrasses need to grow new plants to stay strong. This process is called sexual recruitment. It helps them grow in new places and change with their environment.

Some seagrasses make small seeds that wait before they grow. These plants live a short time but can grow back fast after trouble. Other seagrasses make seeds that can travel far to find better places to grow. One special seagrass, Posidonia oceanica, can live for thousands of years and makes big underwater meadows. Its seeds have extra food to help new plants grow, even when they can't get much sunlight. These new plants also grow special roots to hold them to the ocean floor.

Intertidal and subtidal

Seagrasses that grow in the intertidal and subtidal zones face very different conditions because of tides. Subtidal seagrasses often get less light because of things in the water that block the light. These seagrasses can be studied quickly using smart computer programs. Intertidal seagrasses are often out of the water and face big temperature changes, very bright sunlight, and drying out.

In contrast, subtidal seagrasses live under water and adapt to low light by having longer leaves and wider blades, which helps them grow more. Because their environments are so different, intertidal and subtidal seagrasses act in very different ways to use light best for their growth.

Seagrasses need carbon to grow, and they can use both carbon from the air and from water. Even when intertidal seagrasses are out of the water, they can still use carbon from the air to survive.

Seagrass meadows

Seagrass beds, also called meadows, can be made of one plant or many mixed together. In cooler areas, usually just one or a few kinds of seagrass grow, like eelgrass in the North Atlantic. But in warmer places, like the Philippines, there can be many different types growing together.

Seagrass meadows are important homes for many sea creatures. They give shelter and food to fish, turtles, manatees, and many smaller animals. The plants help keep water clean and clear by trapping dirt and slowing down the water. They also help protect shorelines from big waves and storms. Because seagrasses live underwater, they make a lot of oxygen, which helps all the sea life. These meadows store a lot of carbon, helping to keep our planet healthy.

Seagrass microbiome

Further information: marine microbiomes

See also: plant holobiont

The idea of a holobiont shows how a plant and its tiny living partners, like bacteria and viruses, work together. This teamwork helps the plant get nutrients, stay healthy, and grow. Scientists study this in many plants, including seagrasses.

Most studies look at a type of seagrass called Zostera marina. These tiny partners change depending on where they are on the plant. Some help protect the plant, while others help it grow. Scientists are still learning about these tiny partners and how they stay with the plant.

Research on these tiny partners has grown with better tools. Scientists now study different parts of the plant and different places to see how these partners help seagrasses stay healthy and grow. They also look at how changes in the environment affect these tiny partners.

Threats and conservation

Seagrasses are important plants that live in the ocean. Sadly, these plants have been disappearing more and more over time. Some types of seagrass are now at risk of disappearing completely.

People and nature both harm seagrasses. Human activities like building along coastlines, driving motorboats, and certain fishing methods can damage seagrass areas. Changes in the climate, such as rising sea levels and warmer temperatures, also hurt seagrasses.

Conservation is very important to protect seagrasses. Learning more about these plants and their value is a big step. Scientists are working hard to study seagrasses and find ways to save them. Some countries are starting to make plans to protect seagrass areas and raise awareness about their importance.

Each year on March 1, World Seagrass Day is celebrated to remind people how important seagrasses are to our oceans.