Asian Clam

''Corbicula fluminea'' is a species of freshwater clam native to eastern Asia which has become a successful invasive species throughout the world, including North America, South America, Europe, and New Zealand. It is native to 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. (2001): Nonindigenous species information bulletin: Asian clam, ''Corbicula fluminea'' (Müller, 1774) (Mollusca: Corbiculidae)
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/ref> ''Corbicula fluminea'' is commonly known in the west as the Asian clam, Asiatic clam, or Asian gold clam. In Southeast Asia, ''C. fluminea'' is known as the golden clam, prosperity clam, pygmy clam, or good luck clam. In New Zealand, it is commonly referred as the freshwater gold clam.

Right and left valve of the same specimen:

File:Corbicula fluminea 01.jpg, Right valve
File:Corbicula fluminea 02.jpg, Left valve

Overview

''Corbicula'' have had global success as an aquatic invasive species, having been introduced to a novel range including South America, North America and Europe. Human industrial activity, such as transport of larvae via ballast water in container ships, has been noted in the literature as a chief invasion vector. A market exists for Asian clams for human consumption in Japan, China, and other countries in the region. According to the United States Geological Survey, ''C. fluminea'' is likely to continue to expand its North American range until it reaches the maximum extent of its low temperature tolerance. The periostracum of the shell is normally yellow-green, brown, or black with concentric growth rings of the prismatic layer visible through the proteinous outer layer. The periostracum can flake, allowing the white prismatic layer to show through. The shells exhibit a light purple nacre on the inside.

As a filter feeder, ''Corbicula'' strains suspended contents of nearby water and absorbing material to feed itself. Large quantities of toxins are absorbed in their gut, accumulating high concentrations of toxins. The clams excrete large quantities of inorganic chemicals, such as nitrogen and phosphorus, after feeding off sediment. Despite edibility of ''Corbicula'' in native countries, ''Coribicula'' sourced from New Zealand's Waikato River is considered not safe to eat, as caused by pollution in the river.

''Corbicula'' is a successful breeder in the rivers and lakes of many countries in the world, breeding densely in localized water, and transported elsewhere via water currents or by the movement of humans and their waterborne apparatus. This allows them to outcompete against native invertebrates, including mollusks such as mussels, for phytoplankton as food. ''Corbicula'' has shown to interfere with water-based infrastructure created by humans, such as water treatment and hydroelectric dams, by clogging them up.

Life cycle

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.McMahon, R.F. (1999) Invasive Characteristics of the Freshwater Bivalve ''Corbicula fluminea''. In R. Claudi & J.H. Leach (Eds.), ''Nonindigenous Freshwater Organisms: Vectors, Biology, and Impacts'' (pp. 315-343). Larvae are ~200 microns in length when discharged from an adult and dispersed through water until becoming sessile adults. Adults can reach a length of about .

Feeding

''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). 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.

Taxonomy

''Corbicula fluminea'' is a species of freshwater clam, an aquatic bivalve mollusk in the family Cyrenidae.Bouchet, P. (2015). Corbicula fluminea (O. F. Müller, 1774). In: MolluscaBase (2015). Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=181580 on 2015-08-26 ''C. fluminea'' is often confused with '' Corbicula fluminalis'' due to the two species' similar color and texture. Two species may be present in some introduced populations: ''C. fluminea'' and ''C. fluminalis''. The names themselves are sometimes confused in the literature (e.g. by being called ''"Corbicula fluminata"'').

The ratio of width and height in ''C. fluminea'' is on average 1.1. In ''C. fluminalis'' it is smaller (0.97); still, there is much variation and considerable overlap in shape. Most easily, they can be distinguished by the number of ribs on the shell; ''C. fluminea'' has 7 to 14 ribs per cm, ''C. fluminalis'' 13 to 28. This character is already clearly recognizable (albeit only by direct comparison) in very small (5 mm diameter) specimens. In addition, when viewed from the ventral side (looking at the opening between the shells), ''C. fluminalis'' is rounder, almost heart-shaped, while ''C. fluminea'' has a slightly flatter shape like a teardrop with a notched broad end. Small specimens of ''C. fluminalis'' are almost spherical, while those of ''C. fluminea'' are decidedly flattened. All these differences except the rib number are a consequence of ''C. fluminalis'' having a markedly more swollen, pointed and protruding umbo.

Range

As a native species

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.

As an invasive species

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

*British Columbia circa 1924, and now more widespread
*The Columbia River in the northwest United States in 1938
* United Kingdom, first discovered in 1998 in the River Chet, Norfolk Broads. Found in River Thames in 2004
*Cuba
*Lake Tahoe, on the borders of California and Nevada, they were first found in 2002, and the numbers increased rapidly after 2008.
* Lake George, NY, USA
*South America, including Argentina, Uruguay, Brasil (Río de La Plata basin, Río Amazonas Basin, Patagonia - Río Colorado, Río Negro- and is currently in expansion), Perú, Venezuela 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 (2004): Die Molluskenfauna der Elbe in Mecklenburg-Vorpommern mit Erstnachweis der Grobgerippten Körbchenmuschel ''Corbicula fluminea'' (O. F. Müller 1756). ''Mitteilungen der NGM'' 4(1): 85-89. PDF fulltext

*River Nore & Barrow, Republic of Ireland, first recorded in April 2010
* List of molluscs recorded in the Czech Republic">Czech Republic - in Elbe in Bohemia since 2000 Horsák M., Juřičková L., Beran L., Čejka T. & Dvořák L. (2010). "Komentovaný seznam měkkýšů zjištěných ve volné přírodě České a Slovenské republiky. [Annotated list of mollusc species recorded outdoors in the Czech and Slovak Republics]". ''Malacologica Bohemoslovaca'', Suppl. 1: 1-37
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and it is spreading. It was found in Morava River in south Moravia in 2018.
* Slovakia
*Minho River in Portugal
* Between August 15–28, 2020 in Briggs Lake in Minnesota; however UMN Extension does not believe they are able to naturally survive in Minnesota, instead surviving only in the higher temperatures of power plant coolant water
* Shuswap Lake, British Columbia, Canada in 2020
* Found in the Pend d'Oreille River in British Columbia, a tributary of the Columbia, in the spring of 2021
* First discovered in the Waikato River in the Waikato Region of New Zealand, in May 2023. Ministry of Primary Industries along with the Waikato Regional Council had found the species at Bob's Landing, Lake Karapiro - upriver from Hamilton, New Zealand's fourth most populous city. The clams have successfully colonized throughout a portion of the Waikato River. As a precaution against further spread of the clams, numerous lakes and rivers were closed off, and many other regions have installed mandatory QR codes and permanent washing stations.

Means of dispersal

Human vectors

Human activities are the chief reason for the wide dispersal of ''C. fluminea'' as an invasive aquatic organism. Its global invasion probably started with Asian immigration in North America during the 1920s, as it was used as food source by these communities. ''Corbicula fluminea'', along with other exotic bivalve larvae, may be accidentally transported via ballast water or recreational boaters. Furthermore, the species is common in the aquarium trade and can be intentionally or unintentionally released in the wild by aquarists.

Life history advantages

''Corbicula 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,

''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 . This allows ''C. fluminea'' to colonize novel habitats at an advanced rate.

Habitat association

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. 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 coarse sand combine to explain 59.3% of ''Corbicula'' population habitat association via statistical tests. Asian clam invasions seem to be limited by elevation (88% of the invaded range is below 500m elevation), latitude (90% lies between latitudes 30°and 55°) as well as the minimum winter temperature () of the ecosystem.

Impacts on invaded ecosystems

''Corbicula fluminea'' reworks the sediments it resides on through the process of bioturbation. Asian clams are considered biodiffusors similar to marine clam species due to their observed bioturbation activity which may negatively affect other members of the benthic community in invaded areas. Excessive excretion of inorganic chemicals such as nitrogen and phosphorus imbalance concentrations of oxygen in the water, encouraging the growth of algae and cyanobacteria, as a byproduct of the excretion of these clams.

''Corbicula'' has also been shown to profoundly influence community dynamics within the macrobenthos of invaded systems. ''Corbicula'' has been shown to remove as much as 70% of phytoplankton biomass in reaches of invaded rivers with a robust clam population. 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.

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. Ecologically, ''C. fluminea'' contributes to declines and replacement of highly vulnerable, already threatened native clams.

Global invasion pattern

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.

''Corbicula'' was discovered in New Zealand along a stretch of the Waikato River in May 2023. According to the Ministry of Primary Industries, the clams have likely populated in the river for several years prior to discovery. Based on patterns of unsuccessful eradication of ''Corbicula'' overseas, eradication of ''Corbicula'' is predicted to be near-impossible in New Zealand.

Mitigation

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. In August 2020 routine inspections in Wyoming found several watercraft to be heavily infested including one with ''C. fluminea''. On October 16, 2020, the Montana Department of Fish, Wildlife and Parks recommended that Lake Elmo — in Billings — be drained to dry out and freeze to death the ''C. fluminea'' there.

See also

* List of introduced molluscs species of Venezuela

References

* Weitere, M. et al. (2009) Linking environmental warming to the fitness of the invasive clam Corbicula fluminea, Global Change Biology, Volume 15 Issue 12, Pages 2838 - 285

Further reading

*

External links

USGS (NAS)- Nonindigenous Aquatic Species


* ttp://lanwebs.lander.edu/faculty/rsfox/invertebrates/corbicula.html Anatomy of ''Corbicula fluminea'' Invertebrate Anatomy OnLine

GLANSIS Species Fact Sheet
United States Geological Survey
Species Profile - Asian Clam (''Corbicula fluminea'')
National Invasive Species Information Center, United States National Agricultural Library. Lists general information and resources for Asian Clam.

{{DEFAULTSORT:Corbicula Fluminea
Cyrenidae
Molluscs described in 1774
Taxa named by Otto Friedrich Müller