Seagrass meadows may not be the most striking of marine habitats at first glance, but they are one of the most productive ecosystems on Earth.
These underwater meadows provide food and shelter to hundreds of species, including all-time favourite marine conservation icons like sea horses. Commercially important species also call seagrass meadows home – blue swimmer crabs can be found hiding amongst their leaves, and snapper and luderick can often be seen swimming above meadows.
Seagrasses act as a ‘nursery’ grounds for fish and other critters like prawns. Without the dense canopy that the seagrass provides, predators may eat these critters before they make it into adulthood.
Seagrass meadows are extremely effective at capturing carbon and can slow down climate change by storing carbon up to 40 times faster than terrestrial forests.
The benefits of seagrasses can also be felt on land, as these plants stabilise sediments and protect our shorelines from erosion. Because seagrasses remove dissolved nutrients and sediments from the water column, they also contribute to water clarity.
Finally, seagrasses are also truly remarkable in evolutionary terms. One may think of them as the ‘dolphins’ or marine mammals of the marine plant world: seagrasses are flowering plants with terrestrial ancestors that returned to the sea and re-adapted to the aquatic environment, just like dolphins and whales evolved from four-legged land mammals that returned to the ocean.
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How much can we save?
Declining Posidonia meadows
Posidonia australis is a beautiful and slow-growing seagrass that makes extensive underwater meadows all over southern Australia, from Wallis Lake in New South Wales to Shark Bay in Western Australia.
Unfortunately, seagrasses like Posidonia have become severely threatened by human activities and have been declining at an alarming rate. On average, seagrasses are declining at the same rate as coral reefs, that is – one soccer field every half hour!
In eastern Australia, Posidonia meadows are found in sheltered bays, which are also preferred sites for us humans: this is where we often choose to live, work and play. Increased coastal development and pollution in these sheltered estuaries has led to major Posidonia declines over the last few decades.
The declines of Posidonia meadows in the central parts of NSW (where most people live) have been so severe that six meadows have been formally listed as ‘endangered’ by both the Australian Commonwealth Government (EPBC Act) and the NSW government. There’s a very real risk that this species may become locally extinct from some of these estuaries within the next 15 years unless new conservation actions reverse current trends.
To reverse this decline and prevent further losses, there are now strict regulations that limit coastal development near seagrass meadows, and water quality has greatly improved in the last couple of decades, as we’ve become better at managing waste and reducing pollution.
There are still some human activities that continue to be a problem, however, and are leading to the continued decline of Posidonia in some estuaries. Boat moorings are one of the most obvious current disturbances to seagrass habitats, as the sheltered bays where this seagrass naturally thrives are also the most ideal locations for people to moor their boats.
The problem with traditional, fixed block-and-chain boat moorings is that they scar the seafloor and remove seagrass shoots, causing the formation of bare patches that fragment the meadow and destabilise the sediment. After some time, as the mooring scars get larger, bare patches start to merge and this leads to more Posidonia losses.
Mapping has shown that mooring scars can be very large, form quickly and can take decades to recover fully once a mooring is removed.
Mooring scars are clearly visible from the water’s surface and have been increasing as the number of moorings has raised. Across all of NSW, currently leased moorings are causing losses of around 130,000 m2 (that is more than 26 football fields!), but the real loss is even greater, as many estuaries contain old scars that remain after the relocation of moorings.
The aim of Operation Posidonia is to bring this seagrass back, along with the critters that live within its meadows.
Environmentally friendly moorings coupled with Posidonia Restoration
The only way to prevent damage to the marine environment by boat moorings is to change their design, so that there are no components dragging along the seafloor.
In recent years, a variety of mooring designs have emerged that prevent chains dragging along the seafloor. These new types of moorings are collectively known as Environmentally Friendly Moorings (EFMs), and they are slowly replacing traditional block and chain moorings in many coastlines worldwide, but are not yet used extensively in New South Wales.
Once mooring chains are removed, however, the natural recolonisation of bare patches by Posidonia can be very slow, especially when mooring scars have expanded and altered local hydrodynamics. In some places it could take over 20 years for a mooring scar to be revegetated by Posidonia naturally.
Our aim is to give nature a helping hand and promote the recovery of Posidonia by combining the restoration of Posidonia in old mooring scars where swing moorings have been removed.
Posidonia restoration is underway!
The scientists behind Operation Posidonia have already done some restoration trials in old mooring scars in Port Stephens that are showing very promising results.
They have deployed jute mats to help stabilise sediments in mooring scars, which also helps to anchor Posidonia fragments. So far, they have recorded ~70% survival rate of seagrass shoots using this approach, which is most encouraging!
We need your help
to bring Posidonia back
Join our Storm Squad
Because Posidonia is a protected species classified as ‘endangered’ in many NSW estuaries, one of the greatest challenges for restoration is finding donor shoots to revegetate the mooring scars.
Operation Posidonia has come up with an exciting solution to this problem, but it relies on getting help from local communities.
We are asking 'citizen scientists' to collect donor shoots from their local beach.
Living, green Posidonia shoots often wash ashore after storms, where they will soon perish unless returned underwater. Citizen scientists can collect these detached seagrass shoots and bring them to one of our collection spots. We will then use these shoots to restore seagrass populations without damaging existing Posidonia meadows.
We are aiming is to enlist the help of dog walkers and local beach-goers, who can join a local ‘seagrass storm squad’ and be part of the solution.
It’s all starting in Port Stephens
We are launching Operation Posidonia in Port Stephens, in central NSW. Scientists have selected this location because it represents one of the healthiest estuaries in NSW.
Although Posidonia is currently not threatened in Port Stephens, there are many boat mooring impacts in this estuary (2nd most of any estuary in NSW), with some mooring scars as large as 700 m2.
Port Stephens is also an ideal location because it is the headquarters of Fisheries, NSW Department of Primary Industries, who have led the development of the novel seagrass restoration methods used in this study.
We aim to develop a proof-of-concept restoration method that we can then apply to revegetate Posidonia meadows in other estuaries, where there the species is endangered and there’s a risk it may become locally extinct.