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Nature-based solutions: Seagrass

Kelp image: Shane Stagner

Image: Glen Carbines, NIWA

Blue carbon: seagrass

Summary

  • Seagrasses are found in shallow salty and brackish waters, from the tropics to the Arctic Circle. Unlike seaweeds, they’re closely related to flowering plants on land; they have roots, stems and leaves, and produce flowers and seeds and often grow in dense underwater meadows.
  • Like kelp, seagrass meadows are some of the most productive ecosystems on Earth. They provide shelter and food for diverse communities of animals, from tiny invertebrates to large fish, crabs, marine mammals, and birds.
  • They also drawdown large quantities of carbon dioxide, fix nitrogen in their soils, and crucially, help mitigate the impacts of storm surges by preventing erosion.
  • Dense meadows of seagrass can stabilise the sea bed and reduce erosion. Seagrass leaves trap fine sediments and reduce particle loads in the water by slowing water movement and encouraging particle deposition, which improves the water clarity. Seagrass plants absorb nutrients from the water and seabed. They also release oxygen from their leaves and roots, which is beneficial for other biota and stimulates nutrient cycling.
  • In Aotearoa, significant declines in seagrass meadows took place mostly between
    the 1930s and 1970s in Whangarei, Waitemata, Manukau, Whangamata and Tauranga Harbours, as well as in the Avon-Heathcote estuary in Christchurch.
  • The small crustaceans and worms that live in seagrass meadows are important sources of food for wading birds (such as the South Island oyster catcher, pied stilt, royal spoonbill, bar-tailed godwit) and fish (such as mullet, stargazers and juvenile flatfish). Snapper and leatherjacket juveniles, mullet, trevally, garfish, parore, spotties, pipefish and triplefins are often abundant in subtidal seagrass meadows in particular, but also reside in intertidal meadows when the tide is high.
  • None of this carbon is accounted for under the Emissions Trading Scheme.
  • Risks to seagrasses: polluted water from our rivers. Increasing marine heatwaves means that some species that have adapted to live in cooler waters, are under threat. Ships that release ballast water into harbours also release exotic species.

Image: Glen Carbines, NIWA

Blue carbon: seagrass

Summary

  • Seagrasses are found in shallow salty and brackish waters, from the tropics to the Arctic Circle. Unlike seaweeds, they’re closely related to flowering plants on land; they have roots, stems and leaves, and produce flowers and seeds and often grow in dense underwater meadows.
  • Like kelp, seagrass meadows are some of the most productive ecosystems on Earth. They provide shelter and food for diverse communities of animals, from tiny invertebrates to large fish, crabs, marine mammals, and birds.
  • They also drawdown large quantities of carbon dioxide, fix nitrogen in their soils, and crucially, help mitigate the impacts of storm surges by preventing erosion.
  • Dense meadows of seagrass can stabilise the sea bed and reduce erosion. Seagrass leaves trap fine sediments and reduce particle loads in the water by slowing water movement and encouraging particle deposition, which improves the water clarity. Seagrass plants absorb nutrients from the water and seabed. They also release oxygen from their leaves and roots, which is beneficial for other biota and stimulates nutrient cycling.
  • In Aotearoa, significant declines in seagrass meadows took place mostly between
    the 1930s and 1970s in Whangarei, Waitemata, Manukau, Whangamata and Tauranga Harbours, as well as in the Avon-Heathcote estuary in Christchurch.
  • The small crustaceans and worms that live in seagrass meadows are important sources of food for wading birds (such as the South Island oyster catcher, pied stilt, royal spoonbill, bar-tailed godwit) and fish (such as mullet, stargazers and juvenile flatfish). Snapper and leatherjacket juveniles, mullet, trevally, garfish, parore, spotties, pipefish and triplefins are often abundant in subtidal seagrass meadows in particular, but also reside in intertidal meadows when the tide is high.
  • None of this carbon is accounted for under the Emissions Trading Scheme.
  • Risks to seagrasses: polluted water from our rivers. Increasing marine heatwaves means that some species that have adapted to live in cooler waters, are under threat. Ships that release ballast water into harbours also release exotic species.

New Zealand is well suited to this Greenfield form of carbon sequestration due to the presence of submarine canyons leading to very deep water around its continental shelf. Blue Carbon contrasts sharply from carbon sequestration by traditional terrestrial forestry. Terrestrial forestry is only able to store carbon in a living form and, therefore, reaches maximum storage capacity very quickly. Furthermore, commercial plantation forestry systems become net carbon emitters after 90 to 140 years due to the emissions produced in forestry management, logging, milling and transportation. ” – Blue Carbon NZ

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