Asian clam

This species is of originally mainly Asian origin and thus it is often commonly called Asian clam or Asiatic Clam. In Southeast Asia it is known as the prosperity clam or good luck clam.

This species has been introduced into many parts of the world, including North America and Europe.

Right after reaching maturity these clams produce eggs, followed by sperm. Even later, they produce eggs and sperm simultaneously. They can self-fertilize, and release up to 2,000 juveniles per day, and more than 100,000 in a lifetime. Juveniles are only 1mm long when discharged, and take one to four years to reach maturity. At this time they are about one centimeter long. Adults can reach a length of about 5 cm.

The outside of the shell is normally yellow-green with concentric rings. The color can flake, leaving white spots. The shells are lightly purple on the inside.

They feed primarily on phytoplankton (algae), which they filter from the sandy or muddy bottom of streams, lakes, or canals.

Corbicula fluminea is an invasive species that has proved to be harmless to the general freshwater environment.

Distribution

Invasive species

Originally an Asian species, C. fluminea was probably brought to North America by Asian immigrants, at the latest in 1924, who used them as a food source. The clams are abundant in the Albemarle region of North Carolina as well as other areas along the east coast.

It was first found in the Rhine in the late 1980s and subsequently found its way into the Danube through the Rhine-Main-Danube Canal. It reached the Elbe in 1998 at the latest.² It is non-indigenous in Elbe in Bohemia (Czech Republic) since 2000³ and it is spreading.⁴

Taxonomy

There are obviously two species present in introduced populations, C. fluminea and Corbicula fluminalis⁵. However, they are often mixed together or even confused (e.g. being called "Corbicula fluminata") in the literature, and care needs to be taken to properly distinguish between the two. The rate between 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 amount of ribs on the shell; C. fluminea has 7 to 14 ribs per cm, C. fluminalis 13 to 28⁶. This character is already clearly recognizable (albeit only by direct comparison) in very small (5 mm diameter) specimens. In addition, when viewed from the 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 (the oldest part of the shell valves, close to the ligament holding them together).

References

^ USGS (2001): Nonindigenous species information bulletin: Asian clam, Corbicula fluminea (Müller, 1774) (Mollusca: Corbiculidae). PDF fulltext
^ Jueg, U. & Zettler, M.L. (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. [in German] PDF fulltext
^ Beran, L. (2000): First record of Corbicula fluminea (Mollusca: Bivalvia) in the Czech Republic. — Acta Soc. Zool. Bohem., 64: 1-2.
^ Beran L., (2006) Spreading expansion of Corbicula fluminea (Mollusca: Bivalvia) in the Czech Republic. – Heldia 6 5/6: 187-192.
^ It is not entirely clear that this is the correct name (Jueg & Zettler, 2004)
^ Jueg & Zettler (2004), and see "External links"

Contents

Distribution

Invasive species

Taxonomy

References

External links