Biology

Invasive species (13): the Asian clam

The Asian clam , Corbicula fluminea , is a bivalve mollusk native to Asia that has become invasive in recent decades in different countries and threatens native freshwater species.

Story of a golden clam

As its name suggests, the Asian clam is native to that continent. Its natural range of distribution is quite wide, from Russia to Japan or Indonesia. In Asia it is a common food and the clam is well integrated into ecosystems. It can also be found naturally in various fresh waterways in Africa.

Invasive species
Invasive species

Some of the common names for this species in Asia are fortune clam or golden good luck clam.

The shells are a few centimeters long and the specimens can live to a respectable age of 7 years . This is little compared to other species of clams, such as Arctica Islandica , whose individuals live for centuries (the oldest known animal, 507 years old, belonged to this species).

The Asian clam was introduced to the US in 1924 (some sources indicate that it was in 1938) by Asian immigrants, who released it into rivers to later fish and feed on clams.

In 2002 a population of this mollusk was detected in Lake Tahoe, and since then the population has increased about 100 times its size. It is present in 46 states, practically the entire country.

In Europe it was introduced relatively recently, being the first reference in the river Rhine in 1980. Later it reached other great rivers such as the Danube, the Elbe, the Minho or the Ebro.

The species has been classified as invasive in several countries, including Spain, due to the rapid growth of its populations since it endangers native species due to the competition it exerts on them. Another problematic species in these ecosystems is the zebra mussel, Dreissena polymorpha.

The Asian clam as an invasive species

The problems caused by this species are the same as those caused by the zebra mussel : displacement of native species due to competition and blockage of water conduits, with the consequent economic expense involved in cleaning them. Unlike the zebra mussel, the Asian clam does not adhere to surfaces as spectacularly, instead blocking pipes by the simple accumulation of empty shells.

In the US, because the species was introduced almost a century ago, its expansion is more advanced than in Europe. The costs directly associated with the Asian clam run into several billion dollars . Several nuclear power plants had to pause their activity to carry out a thorough cleaning of their cooling systems.

Invasive species
Invasive species

A species directly threatened by the Asiatic clam is the auriculate naiad or margaritone, Margaritifera auricularia . This mollusk, present only in the Ebro river, is one of the most threatened species in the entire Iberian Peninsula . Its population has been in decline since the 20th century, and the introduction of species such as the zebra mussel or the Asian clam exacerbates its precarious situation.

One of the factors that contribute to the rapid expansion of the Asian clam compared to indigenous species is that their life cycle is different. The larvae of many river clams need to live for a time as parasites on the gills of freshwater fish. In contrast, the larvae of the Asian clam can survive directly in river water.

This is a great advantage over other species, which depend on the presence of fish in rivers to complete their life cycle. In addition to the fact that the Asian clam is capable of surviving in harsher environments, with relatively high or low temperatures, high salinity and pollution, we have the formula for the Asian clam to spread uncontrollably through rivers throughout Europe.

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