Corbicula fluminea

Right after reaching maturity, these clams produce eggs, followed by sperm. Throughout adult life, Corbicula is a self-fertile simultaneous hermaphrodite which can broadcast spawn up to 570 mucoid larvae per day per individual, and more than 68,000 per year per individual[5]. Larvae are ~200 microns in length when discharged from an adult and dispersed through water until becoming sessile adults[5]. Adults can reach a length of about 5 cm.

Corbicula fluminea is an active suspension feeder, and in the process of feeding by pumping water through its body (as well as feeding on interstitial sedimentary material via pedal feeding when suspended grazing items are limited).[6] They feed primarily on phytoplankton (algae), which they actively filter out the water, but may pedal feed on organic matter in the sandy or muddy bottoms of streams, lakes, or canals where the clam establishes a population.[1]

This clam originally occurs in freshwater environments of Eastern Asia, including Russia, Thailand, the Philippines, China, Taiwan, Korea, and Japan. C. fluminea also occurs naturally in freshwater environments of Africa.[7]

Many coastal rivers with a heavy industrial shipping presence in the invaded range of C. fluminea sustain Asian clam populations.[3] Various non-indigenous populations of C. fluminea include:

• British Columbia circa 1924
• The Columbia River in the northwest United States in 1938[3]
• Cuba[8]
• Lake Tahoe, on the borders of California and Nevada, they were first found in 2002, and the numbers increased rapidly after 2008. [1]
• Lake Placid, NY, USA
• South America,[9] including Argentina,[9] Uruguay, Brasil (Río de La Plata basin, Río Amazonas Basin, Patagonia[10][11][12] - Río Colorado, Río Negro- and is currently in expansion), Perú, Venezuela[13][14][15] and Ecuador (Guayas, Daule, Vinces, Quevedo, and Babahoyo River drainages).
• Germany's Rhine River in the late 1980s
• Danube River through the Rhine-Main-Danube Canal.
• It reached the Elbe in 1998 at the latest.[16]
• River Nore & Barrow, Republic of Ireland, first recorded in April 2010[17]
• Czech Republic - in Elbe in Bohemia since 2000[18][19] and it is spreading.[20]
• Slovakia[19]
• Minho River in Portugal[21]

Human activities are the chief vector responsible for C. fluminea's wide dispersal as an aquatic invasive.[3] There is some evidence suggesting that Asian clams followed immigrating Asian communities to North America circa 1924 as a food source.[3] C. fluminea, along with other exotic bivalve larvae, may be transported via ballast water to novel ecosystems and establish populations.[3] The spread of Asian clams has been further exacerbated by other human activities such as the shellfish trade and accidental overland transport by recreational boaters bringing the clam into interior freshwater systems.[3]

C. fluminea enjoys several physiological capabilities which are advantageous in promoting its invasion of novel lentic/lotic environments including:

• Rapid individual growth rate
• Short time to reach sexual maturity
• Short lifespan paired with high fecundity
• Fast rate of water filtration for suspension feeding
• Ability to broadcast gametes over a broad area by utilizing water flow (in rivers)
• Tolerance of a wide variety of substrate/habitat types[22]

Corbicula fluminea is a self-fertilizing, simultaneous hermaphrodite which can asexually produce internally-brooded, semi-buoyant planktonic larvae when spermiogenesis is induced at temperatures above 10°C [5]. This allows C. fluminea to colonize novel habitats at an advanced rate.[22]

Studies on which abiotic habitat characteristics are most strongly associated with Asian clam population abundance have produced varying results. Brazilian habitats have been found to have support the largest abundances of invasive Corbicula spp. in areas with coarser dominant sediment fractions, while negatively correlated with increasing levels of organic matter.[23] Others studies have shown abiotic habitat characteristics such as water redox potential, inorganic nutrient content, hardness, and organic matter content in tandem with the amount of very course sand combine to explain 59.3% of Corbicula population habitat association via statistical tests.[21] Asian clam invasions seem to be limited by elevation (88% of the invaded range is below 500m elevation[1]), latitude (90% lies between latitudes 30°and 55°[1]) as well as the minimum winter temperature (-10°C) of the ecosystem.[1]

C. fluminea reworks the sediments it resides on through the process of bioturbation.[6] Asian clams are considered biodiffusors similar to marine clam species due to their observed bioturbation activity which may negatively affect biogeochemical affect other members of the benthic community in invaded areas.[6]

Corbicula has also been shown to profoundly influence community dynamics within the macrobenthos of invaded systems.[24] Corbicula has been shown to remove as much as 70% of phytoplankton biomass in reaches of invaded rivers with a robust clam population[25]. The clam has also been reported as causing a decline of dissolved oxygen in the water of the same river system with wide ranging second-order effects.[25]

The primary economic and social impact of the invasion of C. fluminea has been billions of dollars in costs associated with clogged plumbing and, heat exchangers, or other human-created infrastructure[26]. Ecologically, C. fluminea contributes to declines and replacement of highly vulnerable, already threatened native clams.[27]

The first recorded instance of Corbicula presence in the scientific literature in the Western Hemisphere was of its introduction into British Columbia circa 1924, followed by a spread throughout the Pacific Northwest and across the American south through South America. Invasions in Europe and Central America were more recent, first appearing in Caribbean countries in 1998.[1]

They have been blamed for algal blooms and concerns exist they will outcompete and displace native species such as the montane pea clam (Pisidium spp.) and the ramshorn snail (Planorbidae).Efforts are underway at Lake Tahoe to smother the clams on the bottom with rubber mats.[28]