Can Science and Tradition Save NSW's Seagrass Meadows?
Beneath the tranquil surfaces of New South Wales' estuaries, a silent crisis is unfolding, threatening the very fabric of these aquatic ecosystems.
Beneath the shimmering surface of New South Wales' coastal waters lies a hidden forest of extraordinary importance. These seagrass meadows, particularly those dominated by the endangered Posidonia australis, form the bedrock of healthy estuaries and embayments. They are marine nurseries, coastline protectors, and powerful carbon sinks all at once.
Yet, these underwater grasslands are vanishing at an alarming rate. Researchers estimate that 50% of the seagrass habitat in places like Gamay (Botany Bay) has already been lost, pushing this critical ecosystem toward localised extinction 1 . This article explores the race against time to save these underwater forests—where cutting-edge science and Indigenous knowledge are converging to rewrite the fate of NSW's seagrass meadows.
Seagrasses are not merely plants that grow in the sea; they are foundation species that architect entire ecosystems. Professor Adriana Vergés, a marine ecologist at the University of New South Wales, explains that Posidonia australis "provides home and shelter for hundreds of other species" and "protects shorelines from erosion" 1 .
These underwater meadows perform what scientists call "ecosystem services"—functions that directly benefit both the marine world and human populations. Their global annual value is estimated at a staggering $11 billion annually 6 .
Seagrass meadows serve as critical nursery grounds for commercially important fish and invertebrate species 6 .
They capture and store significant amounts of carbon, sequestering it in sediments for thousands of years, making them crucial warriors in the fight against climate change 1 .
The grasses increase water clarity and stabilize sediments, reducing coastal erosion and maintaining water quality 6 .
Despite their importance, the seagrass meadows of southeastern Australia are in trouble. The situation is particularly dire for Posidonia australis, which was officially listed as a threatened ecological community in New South Wales in 2010 after suffering historical declines of 12-57% between the 1940s and 1980s 3 .
Alarmingly, the decline has continued even after protective legislation was enacted. Research published in PLOS One demonstrated that these seagrasses continued to decline by approximately 2–40% at 11 out of 14 study sites between 2009 and 2014 3 . In the iconic waters of Sydney Harbour, the analysis revealed an average decline rate exceeding 10% per year—a rate that outpaces the global average for seagrass loss 3 .
This species grows extremely slowly, taking at least a decade to mature and centuries to form extensive meadows 3 .
It recovers poorly after disturbance, suffering from "runaway attrition" where damage begets more damage 3 .
Individual plants may live for hundreds or even thousands of years, making replacement of lost meadows practically impossible on human timescales 3 .
The decline of seagrass in NSW's estuaries results from a confluence of pressures, many stemming from coastal development and human activity.
| Threat Category | Specific Impacts | Example Locations |
|---|---|---|
| Coastal Development | Dredging, construction, smothering by sediment, reduced light penetration | Port Botany, Sydney Airport runways 1 |
| Water Quality Decline | Nutrient pollution, sedimentation from runoff | Various urban estuaries 6 |
| Direct Physical Damage | Anchor dragging, propeller scarring, mooring chain scour | Sydney Harbour, recreational boating areas 3 |
| Climate Change | Temperature extremes, storm events, sea level rise | Across the region 6 |
Anchor dragging and propeller scarring create lasting damage to seagrass meadows, especially given the slow recovery rate of Posidonia australis 3 .
Dredging and construction activities directly remove seagrass habitats while increasing sedimentation that reduces light penetration 1 .
Bidjigal man Bryce Liddell notes from ancestral stories, the bay was once "so thick with seagrass, it was so healthy" that it appeared dark from shore 1 . Today, he says, "the bay looks bare," resulting in a "loss in the culturally significant food species… which means we've lost practices such as cultural fishing" 1 .
In the face of these challenges, a remarkable collaboration is unfolding in Gamay (Botany Bay). The Gamay Rangers, composed of local Aboriginal custodians, have partnered with researchers from UNSW to rebuild the once-thriving marine ecosystem 1 .
This partnership represents a powerful fusion of traditional knowledge and modern science. As Bryce Liddell explains, "We're finding now that we really can't care for our land and sea country the way that we traditionally would have and we need to incorporate modern-day ways of doing things" 1 .
At the heart of their restoration work lies a promising experiment: testing whether biochar can improve the survival and growth of transplanted seagrass 1 .
The team collects viable seagrass fragments that have washed up naturally along shorelines 1 .
The charcoal-like substance, created through controlled burning, is applied to the sediment where seagrass will be transplanted 1 .
Seagrass fragments are carefully replanted in sections of the bay treated with biochar 1 .
Regular diving expeditions monitor the health, growth, and survival of the transplanted seagrass compared to control areas 1 .
Biochar offers multiple potential benefits. As UNSW PhD student Ann Flemming Nielsen notes, "If you want to remove pollutants from an area, it can do that as well" 1 . The experiment also respectfully integrates Indigenous practice, as "burning has been very deeply connected to Indigenous culture for a very long time" 1 .
The early signs are encouraging. Professor Vergés reported after a recent monitoring dive that the replanted seagrass is "bright green, it's growing well," and notably, a blue swimmer crab—a culturally significant food species—was already observed among the new growth 1 .
Seagrass research employs a diverse array of tools and approaches, from traditional field methods to cutting-edge genetic and microbiological techniques.
| Tool or Method | Primary Function | Application in Seagrass Research |
|---|---|---|
| High-Resolution Aerial Imagery | Fine-scale mapping and monitoring | Tracking changes in meadow area and density over time 3 |
| Sediment Coring | Sampling below-ground sediments | Measuring carbon storage (blue carbon) and sediment properties 4 |
| Genetic Analysis | Identifying seagrass genotypes | Selecting restoration material suited to local conditions 6 |
| Microbial Community Analysis | Profiling sediment microbes | Assessing sediment health and seagrass-microbe relationships 6 |
| Biochar | Soil amendment | Improving sediment quality for seagrass transplantation 1 |
Recent research has highlighted the critical importance of sediment processes in seagrass restoration success. The National Environmental Science Program's Marine and Coastal Hub has identified that hydrodynamics, sediment microbes, and interactions with other organisms all play crucial roles in determining whether restoration efforts will succeed 6 .
Successful seagrass conservation requires more than just scientific innovation—it demands community engagement and collaborative stewardship.
Across Australia, partnerships between researchers and community groups are demonstrating promising models. These include collaborations with Indigenous Ranger groups like the Gamay Rangers and Malgana Land and Sea Rangers, and recreational fishing organizations such as OzFish Unlimited 6 . These partnerships involve community members in propagule collection, logistical support, and even scientific data collection 6 .
Avoid anchoring in seagrass beds and minimize travel across them at low tide to prevent propeller damage .
Maintain septic systems, report sewer overflows, and plant native vegetation to reduce sediment runoff .
Avoid walking on seagrass at low tide or digging for bait in seagrass beds .
Choose mesh decking for jetties to allow light penetration and support seagrass-friendly waterfront structures .
The fate of New South Wales' estuarine seagrasses hangs in a delicate balance. These unassuming underwater meadows represent a critical nexus where ecological health, cultural heritage, and climate resilience converge. The work in Gamay demonstrates that while the challenges are significant, the fusion of Indigenous knowledge with scientific innovation offers a promising path forward.
As Bryce Liddell reflects on the returning blue swimmer crabs, his vision extends beyond immediate success: "It also means that I get to, and my kids and my grandkids get to, live off the food source that our ancestors did here in the same area" 1 . In the enduring struggle to save these marine forests, we are not merely protecting plants—we are safeguarding a legacy for generations yet to come.