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Seagrass

underwater meadow of seagrass

The term sea lilies is usually associated with echinoderm animals (or not depending on your interests). This is rather strange as there are about 60 species of flowering plants that grow in the sea, known as seagrass although they are most closely related to the lily family. Pretty messed up huh? Hopefully the gallery below will help and maybe explain the reason for scientific names for organisms.

Background

What is seagrass?

Seagrasses are flowering plants (scientifically known as angiosperms) which grow in marine environments. Seagrasses are not the same as seaweed which is used as a common name for algae which are non-flowering plants. Seagrass can be divided into those that grow continuously submerged and those that grow in intertidal areas. Plants can multiply via rhizome multiplication and also by producing seeds via sexual reproduction.

Distribution

There are about 60 seagrass species worldwide, covering an a coastal length thought to be between 300,000 and 600,000 kilometers. Seagrass distribution is limited by water depth and water clarity because most species require high levels of light to thrive. As plants, they make their own food, utilising the energy of sunlight to turn water and carbon dioxide to a simple sugar and oxygen through the process of photosynthesis.

Services

Carbon capture and storage

Seagrass plants form dense underwater  meadows with extremely high productivity compared to many other ecosystems. Seagrass meadows are able to store carbon dioxide, which contributes to global heating, at a rate 35 times faster than tropical rainforests. The plant’s ability to remove this gas from the atmosphere makes it a vital tool in fighting the climate crisis. In fact, though seagrass meadows currently cover just 0.2% of the seafloor, they absorb 10% of the oceans' carbon each year, making them significant carbon sinks. The average hectare of seagrass stores 139.7 metric tons of carbon in its soil, and studies are also finding deep layers of centuries-old, carbon-rich soil beneath these habitats.

Seagrass ecology

They also provide habitats and food for a diversity of marine life comparable to that of coral reefs. Ecologists and conservationists now recognise seagrass meadows as highly important coastal ocean habitats, holding 40 times more marine life than seabeds without grass. This is especially important for the nurture of young organisms which might otherwise be easy prey for predators such as larger fish.

Erosion control

Seagrasses_prevent_erosion_of_the_seafloor
Seagrasses_prevent_erosion_of_the_seafloor

They contribute to coastal protection by trapping rock debris transported by the sea. Seagrasses reduce erosion of the coast and protect houses and cities from both the force of the sea and from sea-level rise caused by global warming. Seagrass leaves act as baffles in turbulent water that slow down water movement and encourage particulate matter to settle out. Seagrass meadows are one of the most effective barriers against erosion, because they trap sediment amongst their leaves.

Cultural services

To their good fortune, the Comcaac — one of the last hunting-fishing-foraging peoples left in North America — are keepers of an annual variety of eelgrass found nowhere else in the world. For the moment, it and its abundance of edible seed remain safe. Its scientific name — Zostera marina var. atam — echoes the Indigenous name for this blessed plant.1

Summary of services provided for us

  • Sea grass beds capture and store CO2
  • They help maintain water clarity by filtering out fine sediments and particles
  • They stabilize the sea floor with their roots and their rhizomes
  • They provide habitat and nursery areas for fishes, crustaceans and shellfish
  • They are a primary food source for many marine animals, including sea turtles, dugongs, and manatees (tourist attractions) and many fish that we eat.
  • Seagrass seeds have been a food staple for some coastal dwelling peoples for thousands of years.

Threats to the services?

Seagrass meadows are disappearing at an alarming rate, and we’ve already lost an estimated 30% to 40% globally in the last century. In some areas, the loss can be as high as 90% e.g. in parts of Florida's coast.

The decline of seagrasses started in the late 19th century, according to UNEP. Some 7% of seagrass meadows are lost each year; an area equivalent to a football field of seagrass is lost every 30 minutes. At least 22 of the world’s 72 seagrass species are in decline at the global level.

 

Natural Threats

  • Heavy storms, floods and droughts that make water conditions unfavourable (unfortunately, now being exacerbated by human-induced climate change)

Human Threats

  • Irresponsible boating practices leading to damage from anchors and propellers
  • Agricultural and industrial run-off levels which exceed the seagrass’ filtration abilities
  • Destructive fishing practices such as dredging
  • Blocking out of light due to human built infrastructure e.g. docks, boat marinas etc.

What can we do to retain these services?

  • Consideration given to impact on seagrass meadows in all relevant building/development laws
  • Manual restoration projects involving seagrass planting (note: the survival rate of seagrass seeds at about 10%)
  • Raising awareness of the seagrass situation to create political will for funding restoration projects
  • Donate to projects such as HELP RESTORE LIFE-GIVING SEAGRASS MEADOWS
  1. Deep Questions to Ask Planet Ocean [↩]
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