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Facts:

Seagrasses occupy only 0.1% of the seafloor yet are responsible for 12% of the organic carbon buried in the ocean.
1 hectare of seagrass can:
Absorb 35 times more CO2 than a pristine hectare of Amazon Forest.
Produce 100,000 litres of oxygen per day.
Support 80,000 fish and 100 million invertebrates.
Absorb 1.2kg of nutrients per year. Equivalent to the treated effluent from 200 people.
Seagrass meadows are under stress globally.

What is seagrass:

There are an estimated 50–60 named species of seagrass worldwide. Seagrasses are the only flowering plants that grow in the sea, and are thought to be derived from terrestrial plants that colonised the marine environment about 100 million years ago.

Seagrasses are flowering plants (Angiospermae), with stems, leaves, roots and flowers, which have become specialised to grow rooted and submersed in estuarine and coastal environments. While they are named grasses they are not of the grass family Poaceae.

Seagrass gardens under the sea – what are seagrass meadows and why are they important is worth reading.

Seagrass in New Zealand:

New Zealand has only one species of seagrass, which is indigenous Zostera muelleri (rimurēhia). It also occurs naturally in southern parts of Australia. It is recorded as mostly intertidal (exposed at low tide and covered by shallow water at high tide) rather than subtidal (always underwater).

There are some examples of subtidal beds occurring in NZ where the waters are pristine clear, which suggests that subtidal seagrass could once have been a lot more common in NZ coastal waters.

Globally seagrass meadows are declining at an alarming rate of around 7% each year, or an area equal to two football fields every hour. Unfortunately, no systematic survey of seagrass distribution and abundance throughout New Zealand has ever been undertaken, so further research is required.

Zostera muelleri is a small plant compared to some of the larger-leaved specimens that grow elsewhere, particularly in tropical waters. It has thin, olive-green, ribbon-like leaves. The leaves range in size from approximately 5–30 cm in length (but usually around 10 cm) and 0.1–0.4 cm in width.

The project has commenced discussions with researchers on the best methods to use for successful restoration of seagrass meadows in Queen Charlote Sound / Tōtaranui.

The Seagrass carbon storage presentation is worth watching to understand “blue carbon”.

Possible causes for seagrass decline

Thank you to NIWA for producing their great Seagrass Guide and allowing us to use the information.

Seagrass is an important habitat

  • Seagrass meadows are important as they provide shelter and food for fish and marine invertebrates and are foraging grounds for certain shorebirds.
  • Dense meadows of seagrass can stabilise the sea bed and reduce erosion.
  • Seagrass trap fine sediments and reduce particle loads in the water by slowing water movement and encouraging particle deposition, which therefore improves the water clarity.
  • Seagrass plants absorb nutrients from the water and seabed.
  • They sequester carbon very well.
  • They release oxygen from their leaves and roots, which is beneficial for other biota and stimulates nutrient cycling.
  • Decaying seagrass is decomposed by bacteria and fed on by small marine animals (such as snails, bivalves, and crabs), thereby supporting the marine food web.
  • The small crustaceans and worms that live in seagrass meadows are important sources of food for wading birds and fish.
  • Productive seagrass meadows will also support larger fish species such as snapper, so therefore they play a role in recreational and commercial fisheries.

Get involved!

The animals and plants of Tōtaranui need your help now!