Summary

• Seagrasses are found in shallow salty and brackish waters, from the tropics to the Arctic Circle.
• There is just one species in Aotearoa, rimurēhia (Zostera muelleri). Significant declines occured mostly between the 1930s and 1970s in Whangarei, Waitemata, Manukau, Whangamata and Tauranga Harbours, and the Avon-Heathcote estuary in Christchurch.
• 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.  The small crustaceans and worms that live in them are important sources of food for wading birds (such as the South Island oyster catcher, pied stilt, royal spoonbill, bar-tailed godwit) and fish: snapper and leatherjacket juveniles, mullet, trevally, garfish, parore, spotties, pipefish and triplefins.
• Dense meadows of seagrass can stabilise the sea bed and reduce erosion. Their leaves trap fine sediments and reduce particle loads in the water by slowing water movement and encouraging particle deposition, which improves water clarity.
• While they cover only about 0.2% of the ocean, they absorb around 10% of the CO2 (Video 2).
• They also absorb nutrients from the water and seabed, and fix nitrogen in their soils, and then release oxygen from their leaves and roots, which is beneficial for other biota and stimulates nutrient cycling.
• 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. Coastal squeeze limits their ability to move inshore as sea levels rise. The loss of seagrasses could lead to a negative trophic cascade.