The invasive gold clam (Corbicula fluminea) is native to Southeast Asia and is widely established in North and South America and Europe. In New Zealand, it was first discovered in May 2023 in the Waikato River at Bob's Landing, within Lake Karāpiro. It has been declared an unwanted organism under the Biosecurity Act.
Breeding
Gold clams are hermaphroditic, meaning they possess both male and female reproductive organs and can self-fertilise; a significant advantage for their rapid population growth. Fertilisation occurs within the paleal cavity inside the shell, and their fertilised eggs are incubated in the inner demibranchial water tubes within the gills. This sheltered, nutrient-rich environment allows the fertilised eggs to develop safely into larvae until they are ready for release.
Larvae
Once mature, the larvae are released into the water column. Being very small (around 200 micrometers or the size of a grain of sand), the larvae can be easily dispersed by water currents and human activities. During their pediveliger stage, the clams are fully formed and capable of anchoring themselves to sediments, vegetation, and other hard surfaces using mucilaginous byssal threads. This dispersal mechanism helps the gold clam to spread rapidly across different water bodies.
Juvenile
Juvenile gold clams settle into the sediment and attach to surfaces using their byssal threads, allowing the clam to stay in place despite water currents and other disturbances. They have high filtration rates and efficiently convert ingested food into biomass, which enable them to reach sexual maturity within 3-8 months after fertilisation. While juveniles can be moved around by water disturbances, they are highly adaptable and can survive in various aquatic environments.
Adult
Adult gold clams have a lifespan of 1-5 years and are known to spawn multiple times per breeding season, depending on environmental conditions. They have high reproductive rates, with an average individual producing ranging from 1,000 to 100,000 larvae per season. Adults can thrive in a wide range of habitats, including well-oxygenated rivers, oligotrophic lakes, and turbid waters. They can tolerate a broad range of temperatures, although temperatures above 37 C and below 1 C have been reported to inhibit spawning.
Disclaimer: Much of the information presented here is based on international literature. As part of the gold clam programme, NIWA is actively researching the reproductive ecology of the gold clam in a New Zealand context. As new findings emerge, this page will be updated accordingly.
