Seagrass monitoring and restoration

Why is seagrass important?

Many people may know seagrass as that brown smelly stuff that washes up in big piles on our sheltered beaches from time to time. Seagrass is however, much more than that, and forms an extremely important part of marine ecosystems.

Seagrasses are marine flowering plants that form extensive shallow-water meadows in sandy, sheltered bays, such as Nepean Bay on Kangaroo Island. They provide habitat for a broad range of fish and invertebrate species, and are also important nursery areas for many species that are commercially and recreationally valuable such as King George Whiting (Sallaginodes punctata). Seagrass meadows also help guard against coastal erosion by stabilising sediments, as well as helping to keep the water clean by cycling nutrients. Seagrass meadows have also been shown to store more than twice the amount of carbon per square kilometre than forests can, which means healthy seagrass meadows are vitally important to help reduce climate change. Degradation or loss of seagrass meadows can therefore have significant flow-on effects for both the marine and terrestrial environment.

One of the biggest threats to seagrasses is poor water quality entering the marine environment from the land. Heavy sediment loads in land runoff increase the turbidity (muddiness) of the water and high nutrient levels promote smothering algal growth on seagrass leaf blades. Both of these effects reduce the amount of light available for seagrasses to photosynthesise and grow.

It is estimated that over the last two decades, approximately 20% of the world’s documented seagrass habitats have been lost, primarily because of human-induced disturbance. Nutrient over-enrichment (eutrophication) has been identified as the most common cause of seagrass decline as it stimulates the growth of epiphytes (algae that grow on seagrass leaves) and opportunistic macroalgae, which in-turn reduce the amount of light available to seagrass for photosynthesis. In Nepean Bay alone, approximately 3500 hectares of seagrass has either been lost or significantly degraded since the 1960s. Most of the seagrass lost was Smooth Tapeweed (Posidonia sinuosa), which has recently been placed on the International Union for Conservation of Nature (IUCN) Red List of threatened species as Vulnerable.

What is seagrass monitoring?

Natural Resources Kangaroo Island (NRKI), together with the community, is aiming to maintain and enhance the state of valuable natural resources in the region. Since 2009, the NRKI coast and marine team has been monitoring the health of seagrass meadows in Nepean Bay to help detect any further loss or recovery. So far no further loss has been detected. NRKI is also trialling several methods of seagrass restoration, including a Community Seagrass Planting Day held each year during mid-January at Brownlow Beach, Kingscote.   

What is being done?

Having healthy seagrass meadows around KI’s coastline is critical in providing essential ecosystem functions, habitat for a diverse range of fauna (including commercially important species) and stabilisation of the seafloor.

Natural Resources KI’s Coast and Marine Program team undertakes regular monitoring of the major seagrass meadows on KI. By towing an underwater video camera beneath a vessel, footage can be recorded and later viewed in the lab to assess the cover and condition of the seagrass. Staff are also trialling revegetation techniques to improve the recovery rate of seagrass meadows, including dropping 25 kilogram sand-filled hessian bags on to the sea bed to provide an artificial surface to anchor seagrass seedlings.

Information collected on seagrass health is also used to help land managers implement and evaluate the effectiveness of on-ground works.

If you would like to be involved in the Community Seagrass Planting Day, or would like any further information about the work being done on seagrass meadows in Nepean Bay, please contact Natural Resources Kangaroo Island on 8553 4444, or email kinrc@sa.gov.au 


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