In the shallow waters off Johor Bahru’s rapidly urbanising shoreline in Peninsular Malaysia, a busy assemblage of crabs, marine worms and mollusks are a sign of recovery. Just over a decade ago, the wafting seagrass meadow they now inhabit had been laid waste by development.
In 2014, dredgers working on a massive land reclamation project to build a “Forest City” at the tip of the peninsula had dispersed plumes of sediment across the Merambong Shoal, one of Malaysia’s most extensive seagrass beds.
Seagrasses, distinct from seaweeds, are flowering plants that form vibrant underwater meadows. Filtering pollutants, cycling nutrients, sequestering carbon and providing habitat for a rich diversity of marine life, they help maintain the health of coastal seas.
While the Department of Environment recognised the harm and issued a stop-work order later that year, the damage was done: Roughly 10 hectares (25 acres) of seagrass meadow had been destroyed. To try to rectify the situation, the developer, Country Garden Pacificview Sdn. Bhd., ramped up mitigation measures and enlisted the help of marine scientists at the University of Putra Malaysia (UPM) to attempt to recover the seagrass.
In a new study, the UPM researchers document the results of their decade-long (2015-25) seagrass restoration and monitoring program at the Merambong Shoal.
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In many nations, there are already rules governing coral reefs, mangroves or salt marshes. [There should be] the same rules for seagrass.
Anitra Thorhaug, marine biologist, Yale University
Their approach, which focused on transplanting seedlings of a combination of fast-growing seagrass species, achieved relatively high survival rates — 66 per cent in some recovery plots. What’s more, as the meadow stabilised, they recorded the natural return of many other types of seagrasses and a boost in animal communities.
“We found four new species records in that particular area, and our colleagues recorded more than 100 species of invertebrates,” Muta Harah Zakaria, a researcher at UPM and lead author of the study, told Mongabay.
The researchers say they hope their insights can help seagrass protection and restoration efforts across the wider Indo-Pacific and demonstrate that seagrass meadows degraded by coastal development can be revitalised, especially when paired with long-term post-planting care and monitoring.
A crucial ecosystem
Together with mangroves and coral reefs, seagrass meadows filter land-based runoff, cycle nutrients and buffer shorelines from erosion. They also provide superb nursery habitat for fish and other marine life that bring nourishment and livelihoods to local communities.
Yet, despite their importance, marine experts consistently warn that seagrass ecosystems remain largely overlooked in national policy and conservation. Malaysia currently lacks official estimates of seagrass cover and rates of loss, although one study estimated the country hosted around 16.3 square kilometres (6.3 square miles) of seagrass meadow in 2018, much of which is under threat from coastal development, dredging, run-off, boat anchoring and typhoons.
Seagrass beds are also increasingly recognised as carbon storage powerhouses and, therefore, crucial to national and global climate goals, further elevating the urgency of their protection and restoration.
However, little is known about the most effective ways to bring them back to areas where they’ve been lost, especially in the tropics. A range of methods have been trialled across Southeast Asia, with varying results.
Transplanting vegetative root stocks and rhizomes can get fast results but can also damage donor sites, whereas collecting seeds and seedlings from healthy habitats typically has a lower impact on donor sites but requires complex off-site storage and cultivation to ensure they’re strong enough to withstand transplantation.
Mix of species boosts survival
At the Merambong Shoal, Zakaria and her colleagues had studied the local seagrasses since 1999. Therefore, they had deep knowledge of the biology of the species and had also trialled a range of planting techniques prior to embarking on their program in earnest.
“Studying the biology is very important,” Zakaria said. “If you understand the biology of the species, how they grow, how they adapt to the environment, then you can transplant them well … We cultured seagrass in our laboratory until we were very confident.”
The team also observed how different species grew naturally in the Merambong Shoal. They noticed a tall and wide-leaved species called Enhalus acoroides flourished around the edges of seagrass patches, while smaller and rapidly spreading species belonging to the genus Halophila tended to thrive in the middle of swards.
“When the Enhalus is established, the smaller [Halophila] species come in to grow together under its canopy,” Zakaria said. “So we realised we’d better plant the bigger seagrasses first, then we could mix in the smaller Halophila species.”
Primed with this information, Zakaria and her colleagues decided to transplant seedlings of four species in total: Enhalus acoroides, and three types of Halophila, collecting their seeds from healthy parts of the Merambong Shoal and germinating them in a laboratory tank.
In total, they planted 8,591 seedlings across 324 square meters (3,487 square feet) recovery plots: first, the larger Enhalus acoroides, whose dense and deep-root systems helped to quickly stabilise barren sandy areas, followed by Halophila ovalis, H. major and H. spinulosa.
The team recorded seedling survival rates of up to 66 per cent in plots planted with a mix of species. This is higher than typically reported for other techniques like direct seeding and vegetative approaches, the study notes. Conversely, survival rates were much lower in control plots planted with only one species, suggesting that planting a combination of species might enhance long-term resilience.
While the damaged area is yet to return to its former richness, monitoring of the seedlings’ growth and survival between 2015 and 2024 revealed nine seagrass species had naturally colonised the recovery plots, creating a diverse sward of 13 of Malaysia’s 17 seagrass species, including H. nipponica, a species never before recorded in the country.
The high survival rates and returning diversity indicate that transplanting seedlings from a mix of species can offer an “affordable and ecologically sustainable” strategy, the study says, particularly at relatively sheltered sites where projects have access to ex situ tanks in which to cultivate seedlings.
Insights to guide regional efforts
Milica Stankovic, a seagrass researcher at Prince of Songkhla University in Thailand, who wasn’t involved in the Malaysia study, said she was particularly surprised to learn about the seagrass restoration success at Johor Bahru. “The Merambong Shoal is one of the clear examples of what land reclamation does to seagrass, so I was really amazed that some of [the seagrass] is growing,” she told Mongabay in an interview.
She noted it’s common knowledge that species diversity enhances the natural resilience of ecosystems. However, for some reason, that’s rarely emphasised when it comes to seagrass restoration.
“Across the region, the restoration studies are so patchy, and we don’t have a clear way forward,” she said. “Everyone is just doing the same thing over and over.” The findings from the Merambong Shoal provide proof that planting a combination of species might be a viable way forward, she said. “It’s very nice to see something actually working.”
There is no silver bullet approach for seagrass restoration, however. The most effective techniques will vary according to which species occur naturally in the area, the local environmental and physical conditions (such as depth and wave energy), and whether the root drivers of ecosystem decline have been properly addressed.
Stankovic said that while there’s no “one size fits all” approach to seagrass restoration, the learnings from Malaysia will be valuable for future seagrass management and restoration across Southeast Asia.
In Thailand, for instance, attempts have been made to reverse widespread seagrass die-offs along the Andaman Sea coast by transplanting Enhalus acoroides seedlings. So far, however, most of these efforts have failed: “The seedlings just die within a couple of months,” Stankovic said. “It would be interesting to see how mixing in Halophila, [as in the Malaysia study], might work out.”
Stankovic cautioned, however, that as interest in seagrass restoration intensifies, marine conservation authorities must improve their oversight of the collection of seeds, seedlings and vegetative material from donor areas. She said that overharvesting reduces the capacity of healthy sites to naturally regenerate and lowers their genetic diversity, factors that exacerbate broader population declines.
The case of the Merambong Shoal underscores the need for clearer regulation and accountability in coastal planning.
Anitra Thorhaug, a marine biologist at Yale University in the US, with more than 50 years of seagrass restoration experience, said seagrass is too often omitted from national development regulations that oblige companies to mitigate the harms their activities inflict on marine ecosystems.
“In many nations, there are already rules governing coral reefs, mangroves or salt marshes,” Thorhaug said. “[There should be] the same rules for seagrass.”
This story was published with permission from Mongabay.com.
