Hidden meadows, rising threats – the story of Malaysia's seagrasses

Subtidal and intertidal seagrass in the waters off Tanjung Kupang, Johor. Locating and mapping these vital but little known habitats known as the ‘lungs of the sea’ is the first step in beginning to protect them. — THOMAS YONG/The Star

WHEN Assoc Prof Dr Jillian Ooi Lean Sim and her team tested the water temperature off Mersing, Johor, recently, the reading was an astounding 41°C.

The team had been working on mapping seagrass meadows in the area and had put a temperature data logger into the water. 

“We found that for a few hours when the tide went down and the seagrasses were in very shallow water in tide pools, the water temperature went up to about 41°C.

“That’s really, really hot. When I put my hand into the water, I felt like it was too burning hot,” recalls the researcher from Universiti Malaya’s Geography Department during an interview with The Star last Monday.

To put it in perspective, this reading was even higher than land temperatures, which in Malaysia usually averages between 21°C and 32°C daily.

But the situation is not limited to Mersing alone. The world’s oceans have seen a phenomenal rise in sea surface temperatures, with 2023 and 2024 figures reaching record heights.

Marine heatwaves are not just bleaching corals, disrupting ecosystems, and forcing certain fish species to move to cooler waters; it’s also affecting seagrass meadows.

Ooi has seen a seagrass meadow that was ‘beautiful and lush’ turn sparse over a few years – ‘It’s very sad to see’. — Handout

The reading of 41°C, says Ooi, is many times higher than what scientists believe is the upper thermal limit for seagrass survival before it starts to die.

“We think it’s around 34°C, 35°C,” she says.

But it’s not just the spikes in sea surface temperatures that Malaysia’s seagrass meadows have to contend with.

Besides the obvious dangers from land reclamation and agricultural chemical run-offs, other impacts from global warming such as sea level rise and stronger monsoon waves and heavier rain are also proving a challenge for seagrass conservation.

Green, green grass

Often mistaken for seaweed, seagrass is the only flowering plant that grows in marine ecosystems, often in shallow, salty, or brackish waters along coastlines. While there are about 60 species of seagrasses – belonging to four families – there are about 16 to 17 recorded species in Malaysia.

Believed to have evolved from terrestrial plants that recolonised the ocean 70 million to 100 million years ago, seagrass meadows act as nurseries for fish and invertebrates and provide food for sea creatures like dugongs and turtles.

The Fisheries Department announced in 2024 that it was studying the possibility of gazetting the waters around Johor’s Mersing cluster of islands to protect seagrass as a means of helping to keep the dugongs that feed on it alive. It is believed there are fewer than 100 of these marine mammals remaining in Malaysian waters.

The islands anchor some of the country’s largest seagrass meadows and are the only place in Peninsular Malaysia where dugongs can be found, according to the department.

However, other than providing forage for marine species, seagrass is also important – essential even – for global climate health.

Research team members collecting data at Tanjung Adang, Johor.— JILLIAN OOI

Similar to mangroves, seagrasses are highly efficient at absorbing carbon dioxide from the environment and storing the climate-warming gas in biomass and sediment, and hence taking a few digits off global carbon emissions.

According to a study in 2012, despite covering less than 0.1% of the total ocean floor, seagrass meadows contribute around 10% to 18% of the oceanic carbon sink and are believed to have an even greater carbon storage capacity than terrestrial forests.

But at the same time that seagrass meadows are helping to mitigate the effects of climate change, climate change is also affecting them.

Battered by the tides

A dugong feeding on seagrass at the Great Fringing Reef, Red Sea. The highly threatened dugong is just one many sea creatures that depend on seagrass. There are reportedly fewer than 100 of these marine mammals remaining in Malaysian waters. — ANETT SZASZI/Ocean Image Bank

Ooi has seen signs of stronger and more extreme storm events during monsoons, while many villagers have recounted that the seagrass meadows used to be larger, with bigger leaves.

In the past few years, coastal villagers, especially in Mersing where the team has been working consistently, have also told of floods which saw a lot of sediment dumped on the meadows.

“The seagrass gets buried under a lot of sand and mud from the floods and suffocates because it cannot photosynthesise,” Ooi explains.

“And then, after the monsoon, you go and see it’s almost like a desert rather than a beautiful meadow. When you dig into the sand, then you find the seagrass all buried underneath, like, barely surviving.”

While the small species of seagrass can withstand being buried for about three to four weeks, longer than that and they start to die due to the lack of light.

“We’ve noticed this in one meadow that we consistently go back to work on with the communities. The meadow used to be so beautiful and lush a few years ago, it’s now very sparse. It’s very sad to see,” she says.

Hope floats

Analysis by Nasa (the US National Aeronautics and Space Administration) found that the global sea level rose by an average of 0.59cm in 2024, higher than the anticipated hike of 0.43cm.

Ooi carrying out an underwater survey. — Handout

The impact of sea level rise on seagrass is partly aggravated by a human response to that rise: building seawalls to guard against erosion. This impedes the seagrass from following the sea level rise and growing naturally further inland.

“As the sea level rises and the water depth over the seagrass gets deeper, this means that they will have less light,” says Ooi.

“Usually, in natural situations, the seagrasses will follow the sea level. If it gets deeper, they will start growing in more shallow areas and further up the beach. They can still cope.

“The problem is now, we build a lot of sea walls,” she points out, adding that the “seagrasses have nowhere to go”.

Despite the various challenges Ooi says she is optimistic about the conservation of the country’s seagrass meadows.

“Right now, seagrass is not a protected habitat. They are not very visible in policy and legislation.

“So it’s really important to first acknowledge that they should be given protection,” she says, citing an example that developers could then be legally required to map the seagrass in their area and report on the impact their development will have.

Welcoming the Fisheries Department’s mapping of Malaysia’s seagrass, Ooi says this will allow researchers and conservationists to know the location of all the meadows in the country, as well as their individual species make-up.

It is also important, she says, that once the map is drawn up, there should be a process to re-map the areas every few years to know their status.

“We need to know where they are first. But five, 10 or 15 years from now, we need to know if those meadows are shrinking or expanding. So once we map them, that mustn’t be the ‘end thing’.

“That is just the beginning.”