Plus is there yet another new mussel invader in California?
Golden mussels may be small, but their impact on aquatic ecosystems is anything but. These invasive species are infamous for their rapid reproduction and ability to spread, quickly infesting waterways across the globe. Native to China and Southeast Asia, they gradually expanded their range within Asia before reaching Argentina in 1991, likely hitching a ride in the ballast water of a commercial ship, and have now spread across five South American countries.
Golden mussels were first detected in North America on October 17 near the Port of Stockton, likely introduced through ballast water from international cargo ships. This poses serious concerns not only for the fragile Delta ecosystem but also for waterways across California, the United States, and beyond.
At the Delta Independent Science Board meeting on January 29, Dr. Thomas Jabusch, a senior environmental scientist supervisor with the California Department of Fish and Wildlife, outlined the department’s ongoing efforts to combat this invasive newcomer.
Detections in California
Golden mussels (Limnoperna fortunei) were first discovered near the Port of Stockton and Middle River on October 17, 2024. They were detected a week later at the O’Neill Forebay and in the California Aqueduct on October 31. They were found in the Contra Costa Canal in mid-November and had reached Bethany Reservoir, the first stop of the aqueduct after leaving the pumps, by the end of the year.
Golden mussels are now in the state’s water conveyance system, and since the State Water Project and Central Valley Project are interlinked, there is concern they will spread throughout the conveyance infrastructure.
However, so far, their range has been limited mostly to the Delta. The map shows the locations where monitoring is being conducted using standard protocols already in place. The red dots show where golden mussels have been detected; the blue are locations where golden mussels have not been detected.
Lifecycle and Reproduction
Golden mussels reproduce by releasing eggs and sperm directly into the water. The fertilized eggs develop into tiny, free-swimming larvae called veligers. Microscopic veligers float in the water column for a few weeks before settling onto surrounding surfaces. Although difficult to see, they can be felt as rough, sandpaper-like patches on submerged objects.
When choosing where to settle, golden mussels favor hard, dark surfaces, particularly in areas close to the water’s surface. A common location for settlement includes the undersides of docks, often in nooks and crannies. Over time, these tiny veligers grow into adult mussels, ranging from one to two inches in length.
The golden mussel has been called ‘dreissenoids on steroids’ as they can reproduce as early as three months old and have an astonishing capacity for reproduction. For example, a single glass of water from an infested area could contain thousands of veligers. Given suitable environmental conditions, these mussels can spawn year-round. This year-round reproduction, combined with their prolific numbers, enables the population to grow at a remarkable rate once established.
Golden mussels also have a wider tolerance for environmental variables such as calcium, temperature, and salinity than quagga and zebra mussels. “For example, they are capable of reproducing at calcium concentrations of about five milligrams per liter, compared to quagga and zebra mussels, which we start worrying about when calcium reaches levels of more than 15 milligrams per liter,” said Dr. Jabusch. “Golden mussels can tolerate higher salinity levels than quagga and zebra mussels, so they can make do in brackish conditions, and their temperature range is fairly high.”
CDFW has an extensive database of calcium and other water quality parameters, so the program did an initial assessment, the results of which are shown on the map. Dr. Jabusch noted that there may be some errors in the map, but the bottom line, all the red dots are areas that might be suitable places for golden mussel establishment. He noted that the other mussels weren’t so much of a concern in areas that primarily receive Sacramento River water, but for golden mussels, the conditions in the North Delta are such that golden mussels could establish.
Ecosystem impacts
Golden mussels are filter feeders, consuming massive quantities of algae from the water. While this might seem like a positive trait, it often does more harm than good. By depleting algae, they reduce a critical food source for many other species, including fish. This disruption at the base of the food chain can ripple throughout the entire ecosystem, forcing native species to compete for resources. Research has linked golden mussels to increased frequencies of harmful algal blooms as they filter out smaller algae, leaving the colonies of microcystis behind.
Additionally, their dense populations can lead to significant biofouling. Large colonies of mussels attach to and clog pipes, damage water infrastructure, and disrupt industries reliant on clean water flow, such as hydroelectric plants and irrigation systems. It can be time consuming and expensive to regularly remove mussels from equipment.
The spread
Golden mussels can spread very fast; in some river systems, they have spread up to 150 miles a year on average. This is mainly attributed to recreational boating, although there are other mechanisms. Mussels have been carried upstream by transporting sand for replenishing beaches.
Another way golden mussels have been found to spread is by being consumed by fish that then swim upstream and die. The mussels are not that digestible and can survive and colonize further upstream.
This map is from the Colorado Watercraft Inspection Database. This data is from participating agencies, and while California as a state is not a participant, many water agencies do. The map is data from 2024 where golden mussels were detected, and the Delta was the watercraft’s last visited water.
“That’s a big concern,” said Dr. Jabusch. “These boats already have been traveling all over the place with no restrictions, so there’s a big concern of the spread with recreational watercraft.”
Containment challenges
The Golden Mussel Task Force is developing a response plan that will address communications, monitoring, containment, prevention, minimizing impacts, and other information. And recently, CDFW held a water agency summit to update them on the golden mussel issue and how to prevent infestations.
However, Dr. Jabusch acknowledged that containment in the Delta will be challenging, given the unmanaged water access for boats and watercraft, the conveyance infrastructure, and limited personnel and funding. So prevention is the goal so to the extent possible, and where it’s not possible, prepare for their arrival.
“There’s places where you can contain them; there’s places where you can prevent them. When quagga and zebra mussels arrived in California in 2007-2008, they were spread with the conveyances in Southern California, mostly initially California Aqueduct, so major changes were implemented. Water Agencies got on board with prevention programs at their water bodies and managing water access, and the boating and fishing community came on board. So that kind of cooperation is important. We have about 40 reported locations of quagga and zebra mussels. Most of them were infested in those early two years. And then that really slowed down.”
Is there yet another mussel invader?
Rachel Meyer, a researcher at UC Davis, has been sharing eDNA results from 2020 archive samples, and the green dots show eDNA hits of golden mussels around the Port of Los Angeles.
“My team did due diligence,” said Dr. Jabusch. “I have staff in Seal Beach, just around the corner. So they went looking for golden mussels and found mussels in a water body called the Dominguez Channel. Where the arrow is, the two yellow dots, is where the mussels were found, and they looked darn close to golden mussels. But the salinity seemed a bit high for the golden mussel to establish. So, we insisted on genetic analysis. And we actually found another invasive species that I want to bring to your attention because it’s a brackish water species called Xenostrobus.”
“We alerted our Marine Region. We’re going to do some follow-up monitoring to see if that’s already an established population. But that’s a new discovery in SoCal, and since it’s a brackish water species, it’s probably something to put on the radar for our estuary up here as well.”
Video: Golden Mussels-Separating Fact From Fiction
This video contains information on the California Delta’s newest invasive species, the Golden Mussel. Steve Cooper, local angler and host of the In Deep On The Delta weekly fishing report is joined by Steve Gonzalez, CDFW Communications Director and Thomas Jobuse, lead CDFW biologist overseeing the golden mussel research. Lot’s of controversy has come to light concerning the Golden Mussel, the video contains science based information directed to all anglers, boaters and environmentalist interseted in preserving the health of the California Delta.
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