Golden mussel (Limnoperna fortunei)

Synonyms: Mytilus fortunei, Limnoperna lacustris, Volsella fortunei

Description:

Golden mussel (Limnoperna fortunei) is a small freshwater mussel from China and Southeast Asia that attaches to almost any underwater surface and fouls it in huge numbers [1][2]. It has spread through shipping to South America and Asia, and it was found in the United States for the first time in California in 2024 [1][2]. MISIN tracks it as a high-priority watch species because it clogs water pipes and boats, strips plankton from the water faster than zebra or quagga mussels, and spreads easily on watercraft [1][2].

Identification:

The golden mussel is a small mussel, usually about 1 inch long and reaching up to about 1? inches (around 20?45 mm) [1]. Its shell is teardrop- or D-shaped, dark brown above a ridge (keel) that runs along the shell and paler golden-yellow below, which gives the mussel its name; inside, the shell is a shiny purple mother-of-pearl above the keel and white below [1]. Like zebra and quagga mussels ? but unlike native freshwater mussels ? it anchors itself to hard surfaces with tough fibers called byssal threads, and it often grows in dense clusters [1][2].

Golden mussels can be found year-round because adults stay attached to surfaces. Check boat hulls, motors, anchors, ropes, docks, pipes, and rocks, and look for the small dark-brown-and-gold shells clumped together [1][2]. This is a new arrival in the United States, so any small freshwater mussel attached by threads ? especially outside the Great Lakes, where zebra and quagga mussels already occur ? is worth a close look and a report [1].

At-a-glance cues:

1. Small mussel, about 1 inch (up to ~1? inch) long, teardrop- to D-shaped [1]
2. Shell dark brown above a lengthwise ridge, golden-yellow below; purple-and-white pearly interior [1]
3. Attaches to hard surfaces with byssal threads, usually in dense clusters [1][2]
4. Encrusts boats, pipes, docks, rocks, and even plants and native mussels [1][2]

Habitat:

Golden mussels live in fresh water ? lakes, rivers, reservoirs, canals, and irrigation systems [1]. They need hard surfaces such as rocks, pipes, docks, and boat hulls to attach to with their byssal threads, but they can also cling to aquatic plants and persist on softer bottoms [1]. They tolerate a wide range of conditions, including warmer water and water with less calcium than zebra and quagga mussels need, which means they could potentially invade more waters than those species [1][2].

The golden mussel is native to the rivers and lakes of China and Southeast Asia [1]. Through shipping it has invaded South America and parts of Asia, and in October 2024 it was found in North America for the first time, in California's Sacramento?San Joaquin Delta and upper San Francisco Bay [1]. Across the rest of the United States, including the MISIN region, it is a watch species ? the goal is to catch and report it before it spreads [1][2].

Reproduction:

Golden mussels spread in two ways that matter to anyone on the water. Their young begin as microscopic, free-floating larvae that drift in the water and are easily moved in any water carried from an infested place ? in a bilge, live well, bait bucket, or motor [1]. The adults attach firmly to hard surfaces, so they ride from water to water on boat hulls, trailers, motors, anchors, ropes, and gear; overland transport on boats is the main way they reach new waters [1][2].

They also breed almost nonstop. Golden mussels have separate males and females that release eggs and sperm into the water, and in warm conditions they spawn continuously rather than in a single yearly burst, so larvae can be present much of the year [1]. They build up to staggering numbers ? from a few thousand up to 250,000 mussels per square meter on hard surfaces ? so a small introduction can become a massive infestation [1]. There is no seed-set window to target; the key is prevention ? clean, drain, and dry boats and gear so neither the larvae nor the adults are carried to a new waterbody (see Management) [1][2].

Impact and Damage:

Golden mussels are not poisonous, but they affect people directly: their sharp shells encrust and clog water-intake pipes and screens at drinking-water, power, and irrigation plants ? a costly maintenance problem ? and they foul boats, docks, and ropes and can cut bare feet [1][2]. They are considered an even worse biofouler than zebra and quagga mussels [1].

The damage to the water itself is severe. Golden mussels are extremely fast filter feeders ? they can strip more than 60% of the tiny plants (phytoplankton) from the water ? which removes the food that native fish and other wildlife depend on and reshapes the food web [1]. In huge numbers they also smother native mussels and other bottom life by attaching to them and crowding them out [1][2]. Because the species reproduces continuously, tolerates a wide range of conditions, and has already caused major economic damage in South America, it is treated as one of the most serious freshwater invaders to keep out of new waters [1][2].

Similar species:

A few small, surface-attaching freshwater mussels can be confused with the golden mussel.

Zebra mussel (Dreissena polymorpha) is a small invasive mussel that also clings to hard surfaces with byssal threads and fouls boats and pipes. It is told apart by its D-shaped shell that sits flat on its hinge side and its bold dark-and-light zigzag striping, rather than the golden mussel's brown-and-gold teardrop shell.

Quagga mussel (Dreissena bugensis) is another byssal-attaching invasive mussel, rounder and paler with darker rings, that tips over rather than sitting flat on its hinge side. Like the zebra mussel it belongs to a different family than the golden mussel and is separated by shell shape and color.

Native freshwater mussels (family Unionidae) are generally much larger, with thick shells, and sit unattached and partly buried in the bottom rather than clinging to hard surfaces with threads. A small mussel cemented by fibers to a rock, pipe, or boat is far more likely to be golden, zebra, or quagga mussel.

Monitoring and rapid response:

Signs to watch for:

1. Small (about 1 inch) dark-brown-and-gold, teardrop-shaped mussels attached by threads to boats, pipes, docks, ropes, rocks, or plants, often in dense clusters [1]
2. Mussel clusters fouling water-intake screens, motors, or hulls [1][2]
3. Any small freshwater mussel attached by threads, especially outside the Great Lakes region [1]

What you can do:

1. Clean, Drain, and Dry every time. Before leaving a lake or river, clean all plants, mud, and animals off your boat, trailer, motor, anchor, and gear; drain all water from the bilge, live wells, bait buckets, and motor; and let everything dry completely ? ideally five days or more ? before entering another waterbody [1][2].
2. Never move water, bait, or aquatic plants from one waterbody to another, and throw unwanted bait in the trash, not the water [1].
3. Inspect boats, docks, ropes, and equipment for attached mussels, and remove and dispose of any you find on land [2].
4. Because this is a new and high-priority invader in the United States, report any suspected golden mussel right away (below), even if you are not certain of the identification [1][2].
5. Lake associations and crews should set up decontamination (hot-water, high-pressure washing) for boats and gear moving between waters, monitor high-use access points, and coordinate with the state aquatic-invasive-species program [2].

When to call a professional:

1. A suspected golden mussel anywhere, or mussels fouling a water-intake system ? contact your state aquatic-invasive-species program immediately, since this is a high-priority new invader and rapid response depends on early reports [1][2].
2. For chemical control options, contact a licensed applicator or your local cooperative extension office.

Report sightings to MISIN. Help track this species' spread by submitting observations through the MISIN web site or the MISIN mobile app (Android, iOS, Windows, and macOS). Photos at multiple angles paired with a precise GPS location are the most valuable data for confirming new occurrences and triggering rapid-response review.

Credits:

1. U.S. Geological Survey, Nonindigenous Aquatic Species Database. Golden Mussel (Limnoperna fortunei) ? Species Profile. nas.er.usgs.gov
2. Washington Department of Fish & Wildlife. Golden Mussel (Limnoperna fortunei). wdfw.wa.gov
3. CABI. Limnoperna fortunei (golden mussel) ? Invasive Species Compendium. semanticscholar.org

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