A mussel calamity has befallen Singapore's northern shores.
Since 2016, a new species of mussel that could have come from as far away as the Americas has spread rapidly along the northern coast, clogging up nets in fish farms and displacing the Asian green mussel native to Singapore, as it competes 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 they will affect the ancient horseshoe crabs, are ongoing. But there is concern that 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 at a media briefing yesterday.
The research was led by Dr Serena Teo and Dr Tan Koh Siang, both senior research fellows at NUS' Tropical Marine Science Institute.
According to the research paper, the mollusc could have come from Brazil, Colombia or Ecuador, where they 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 here by ballast water in ships, noted the study published last month in the science journal Molluscan Research.
Invasive species like the American mussel could hurt Singapore's status as a top transhipment hub. 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 seawater intake pipes and vessels. Such undesirable marine growth on man-made surfaces is known as biofouling. The clumps can reduce vessel speeds by over 10 per cent due to drag, and increase fuel consumption of ships. Engines and propellers can also be damaged.
The National Parks Board (NParks) said it was first made aware of the issue early last year, and it is 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 NUS experts to assess the presence and potential movement of the mussels in Singapore 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.
The Nature Society's marine conservation group chairman Stephen Beng said the invasive mussels have "devastated" the Kranji mudflats, an ecologically important habitat.
"We've noted their encroachment since the end of 2015 but received confirmation that it was an invasive species only much later," he said, calling for parties involved to strengthen collaborative efforts and tighten communication loops in dealing with apparent threats.