SINGAPORE - A mussel calamity has befallen the Republic's northern shores.
Since 2016, a new species of mussel that could have come from as far away as the Americas has been spreading rapidly along Singapore's northern coast, clogging up nets in fish farms and displacing the Asian green mussel native to Singapore, as they compete with the local molluscs for space.
Observed in clumps of up to 10,000 individual shellfish, the invasive American brackish-water mussel has also been forming dense mats in the Kranji mudflats - home to rare horseshoe crabs - to the dismay of nature groups here.
Studies on the impact that the invasive mussels have on local ecology, including how it will affect the ancient horseshoe crabs, are ongoing. But there is concern the appearance of the mussels in the horseshoe crabs' habitat in such dense numbers has made it difficult for the latter to burrow into the sand where the creatures lay their eggs.
This is the first time the mussel Mytella strigata has been recorded in Singapore waters, said National University of Singapore (NUS) scientists studying the phenomenon during a media briefing on Friday (March 2).
The research was led by Dr Serena Teo and Dr Tan Koh Siang, both senior research fellows at the Tropical Marine Science Institute under NUS.
According to the research paper by the six NUS scientists, the mollusc could have come from Brazil, Colombia or Ecuador - countries where these animals are naturally found - or from the Philippines, where they have been introduced since the 19th century.
Larvae from the mussel, which can grow up to 5cm in length, could have been transported to Singapore by ballast water in ships, usually taken on board to provide stability, noted the study, which was published last month in the science journal Molluscan Research.
According to the United States' National Oceanic and Atmospheric Administration (NOAA), invasive species are animals or plants from another region of the world that do not belong in their new environment.
"They can be introduced to an area by ship ballast water, accidental release, and most often, by people. Invasive species can lead to the extinction of native plants and animals, destroy biodiversity, and permanently alter habitats," said the NOAA on its website.
Invasive species such as the American mussel could hurt also Singapore's status as a top transhipment hub globally. The Republic, like many coastal cities with urban harbours, is vulnerable to invasions by such shellfish.
When invasive mussels attach to hard surfaces, they form clumps in places such as on seawater intake pipes and vessels. Such undesirable marine growth on man-made surfaces is known as biofouling.
These clumps can reduce vessel speeds by more than 10 per cent due to drag, and increase fuel consumption of ships when they power up to overcome it. Such marine pests can also damage engines and propellers.
Findings from the NUS researchers' study suggest that the foreign mussels could muscle out their native counterparts in fish farms here.
The researchers placed nylon sheet netting underwater at a floating fish farm off Changi. The netting was first put out in September 2014 and renewed every month between October 2014 and February last year.
Before February 2016, the only mussel species found on the netting was the native Asian green mussel. But since March 2016, the invasive Mytella strigata was observed in rising numbers, and the number of Asian green mussels decreased.
The National Parks Board (NParks), custodian of Singapore's nature areas, told The Straits Times that it was first made aware of the mussels early last year, and that it is currently collaborating with experts from NUS on research to better understand the mollusc.
Dr Karenne Tun, director of the marine division at NParks' National Biodiversity Centre, said the board will be working with experts from NUS to assess the presence and potential movement of the mussels within Singapore's waters using eDNA techniques.
"This would enable us to develop a holistic science-based management plan for the species. At the same time, NParks and the Tropical Marine Science Institute will be working with volunteers from the Marine Conservation Group of the Nature Society (Singapore) on a mussel removal programme at areas most impacted by the mussels," said Dr Tun.
Mr Stephen Beng, chair of the Nature Society’s marine conservation group, said the invasive mussels have “devastated” the Kranji mudflats, an ecologically important habitat.
“We’ve noted their encroachment since end of 2015 but only received confirmation that it was an invasive species much later,” he told ST.
He said parties involved need to strengthen collaborative efforts and tighten communication loops in dealing with apparent threats.
“For now, the horseshoe crab rescue and research volunteers are willing to clear the mussels even if it’s a short term strategy but we want to focus on ecological studies to understand how the species lives and interacts. This will help us develop interventions that may help to manage the spread and hopefully eradicate the problem.
Muscled out: Singapore's native green mussels face competition from foreign species
Fann Sim Channel NewsAsia 2 Mar 18;
SINGAPORE: Singapore's native green mussels are at risk of being displaced by a competing species from the Atlantic waters near South America.
The Mytella strigata, commonly known as charru mussels, was first discovered in our shores by accident in 2016.
In the year since, these foreign mussels have reproduced rapidly, with sightings reported last year at eight other locations including Sungei Buloh, Sungei Jurong and Pulau Ubin, said a team of researchers at the National University of Singapore's Tropical Marine Science Institute.
MUSCLED OUT
At a research site at Changi fish farms, the researchers found that the charru mussels - which grows on hard surfaces such as seawalls and boulders as well as soft sediments like mudflats and mangrove floors - displaced native green mussels by taking over their space.
As part of their study, the researchers placed sheets of nets underwater and reviewed them on a monthly basis.
"What we see on our fishnets is that it's recruiting much, much faster than the green mussels. It'll reproduce. Once you sit first, and you occupy all the space then the other one cannot go in," said Dr Serena Teo, a senior research fellow at the research institute.
"They (green mussels) have less space to settle and grow bigger ... We know that the Mytella Strigata can choose to settle in many places and that also includes the spaces that the green mussels also likes to dominate," said research associate Lim Chin Sing.
"We do not know when it arrived in Singapore but what we have now is a detection when it has spread. Invasive species can come by many, many different routes. Through shipping, aquaculture, people also carry things around. There are a number of ways species can travel," Dr Teo added.
Dr Teo urged the public to not collect or consume charru mussels found in the wild.
Mussels are filter feeders that obtain nutrients by processing large amounts of water they live in.
"While they are consumed in some countries, I think it's important in Singapore that people are a bit more cautious about what they want to collect. Wild collected food carries risk of environmental contaminants whereas what you buy from the market has gone through Agri-Food & Veterinary Authority (AVA)," said Dr Teo.
In the next phase of the study, the researchers will look into the life history of these mussels, such as their reproduction rate and environmental tolerance.
The researchers will also look at the larger impact of their invasive presence on fish farmers and the shipping industry .
HOW DID THEY GET TO SOUTHEAST ASIA?
The earliest record of the charru mussel appearing in the region was logged from a specimen collected from the Philippines in 1800s.
"They could have travelled through the Spanish galleons, maybe like an attachment to the boat or maybe through aquaculture or things that they bring over. These Spanish galleons travelled from America to Philippines in the 16th to 19th century so it could have followed them there and established in the local estuaries in the Philippines," said Ms Lim Jia Yi, an NUS graduate who worked on the study.
The findings were published in the Molluscan Research journal.
Source: CNA/fs
Alien mussel species could hurt local fish farmers
SIAU MING EN Today Online 3 Mar 18;
SINGAPORE — An alien species of mussels spotted here since 2015 has raised alarm among environmental activists and could impact local fish farmers.
Charru mussels, or Mytella strigata, are native to Central and South America. Closer to home, they were established in the Philippines in the 19th century.
The steady growth of the non-native mussels, which have been sighted at multiple locations here such as Sungei Buloh, Pasir Ris, Pulau Ubin and Sembawang, has led to concerns that they could out-compete native Asian green mussels and horseshoe crabs.
At least one fish farmer who also grows shellfish has been affected by the invasive mussels. Ah Hua Kelong co-owner Bryan Ang, 29, first noticed Charru mussels about two years ago at both his farms in Sembawang and Pasir Ris.
“They suddenly just appeared (and) kept growing till the green mussels cannot survive. It’s quite damaging,” he said.
Although not the main source of his business, his farms harvest about five tonnes of Asian green mussels a year. Now, Charru mussels make up about 70 to 80 per cent of his mussel harvest at the Sembawang farm, and about 25 per cent over at Pasir Ris.
“We can’t do anything about it. We can’t sell (the Charru mussels because) nobody is going to buy it, (they’re) so small. They (also) keep growing, like weed. You can clear them but they come back again,” he added.
Asian green mussels, which are bigger than Charru mussels, sell for S$8 per kg on Ah Hua Kelong’s website.
Some other fish farmers here grow Asian green mussels to filter harmful particles from the water around their farmed fish and do not sell the molluscs.
Mr Stephen Beng, chairman of the Nature Society Singapore’s marine conservation group, has seen a steady growth of the invasive mussels at the Kranji mudflats – home to horseshoe crabs – since late-2015.
The invasive species could out-compete the horseshoe crabs for space or strip the mudflats of life-supporting nutrients and cause a shift in the base of the food web, upsetting the ecosystem.
As an immediate response, Mr Beng and fellow volunteers plan to clear the non-native mussels that they find. In the longer term, they hope to conduct ecological studies to understand the interactions between the invasive and native species, he said.
Researchers here, who published a study on the Charru mussels last month, first discovered them on a routine field trip to the shores along the Johor straits in March 2016. It is the first time these mussels have been reported in the Malay Archipelago, said Dr Serena Teo, senior research fellow at the National University of Singapore’s Tropical Marine Science Institute.
The researchers have been studying mussels since September 2014 by placing nets underwater, which are inspected every month.
While it is not known how exactly the Charru mussels arrived at Singapore’s shores, they could have travelled via ballast water in ships or by aquaculture, said Dr Teo.
After the researchers’ first sighting of the Mytella strigata, they noticed the increase in their numbers, while that of the Asian green mussels – the only species previously found on the nets – fell. It meant the invasive species was reproducing much faster and occupying space on the nets, leaving no room for the Asian green mussels, said Dr Teo, who co-led the study.
To identify the new species, the researchers had to examine the interior surfaces of the shells, conduct genetic sequencing and examine museum specimens.
Their presence here could have various implications, said Dr Teo. “With this infestation, farmers may need to consider new ways to efficiently farm (Asian green mussels),” she said.
Besides causing drag in the movement of ships, the species may also find its way to other countries. In places with strict biosecurity laws, the presence of invasive pests can result in penalties for ship owners, she said.
And while Charru mussels can be eaten, Dr Teo cautioned against eating those collected in the wild as they may carry environmental contaminants.
The researchers plan to do further studies in areas such as the species’ growth rates, settlement patterns and how it interacts with other organisms in the ecosystem.
Invasive species are a concern worldwide because they have the potential to destroy biodiversity, alter habitats or cause native species to go extinct.
The Mytella strigata is not the only invasive mussel species here. Another, the Mytilopsis sallei, was introduced in the 1980s.
Other species non-native to Singapore that have found their way into the wild – possibly through the pet trade and abandonment by pet owners – include the Red-eared Slider (a turtle) and the Javan myna (which has become Singapore’s most abundant bird).
Related links
On wild shores of singapore
* Invasive mussels on Singapore's northern shores
* Kranji Clamity Continues, Jan 2018
* Clams and clear water at Kranji, Mar 2017