The Fisheries Research Institute has discovered that a clam farmed in Taiwan is a new species native to Taiwan, and has not yet been described or named other than Meretrix lusoria, which was previously recognized as native to Japan. The relevant research results were published in March, 2023 in the internationally recognized SCI journal "Molluscan Research", and the clam was officially named "Meretrix taiwanica Hsiao & Chuang, 2023".
According to the Fisheries Research Institute, the clam is one of the most economically important shellfish in Taiwan, and mainly inhabits flat sandy beaches in estuaries and sandy sea beds in the intertidal zone. Clam aquaculture in Taiwan began with the stocking of clams during the Japanese colonial period, and due to the good results, the Tamsui River estuary became an important clam seedling production area at that time. Therefore, in the past, it was believed that the M. lusoria clam farmed in Taiwan was introduced from Japan, and the clams in the Tamsui River estuary were also the progeny of the M. lusoria stocked in Japan. However, due to the similarity of the external morphology of M. lusoria, M. petechialis and M. meretrix in shell shape and the wide pattern variations among individuals, identifying the clams was easily confused, thus, the classification of this clam in Taiwan remains ambiguous.
After a series of investigations, the Fisheries Research Institute confirmed with DNA-based identification technology that the DNA sequences of the Taiwanese clam were 9.53% different from those of M. lusoria, and 7.59% different from those of the more closely related M. petechialis. The multivariate analysis of shell morphology also revealed that the Taiwanese clam could be clearly separated from M. petechialis and M. lusoria, thus, it was confirmed that this Taiwanese clam is a new species different from the former two.
According to the Fisheries Research Institute, as M. lusoria has never been found in the sampling surveys in the Tamsui River, it is assumed that the M. lusoria stocked during the Japanese colonial period failed to adapt to the environment and survive, meaning the clams caught in the Tamsui River are native M. taiwanica. In fact, the habitat ecology of the two species is quite different, as M. taiwanica mainly inhabits the intertidal sandy bottom near mangrove forests in estuaries, whereas M. lusoria grows and moves towards estuaries with higher salinity, and the adult clams mainly inhabit the bays. The Fisheries Research Institute further investigated and studied these similar species and confirmed that Meretrix taiwanica is mainly distributed along the coasts of Taiwan and southern China, while M. petechialis is found along the coasts of China, M. lusoria is found in Japan and Korea, and M. meretrix only in Southeast Asia. Therefore, Meretrix lusoria, M. petechialis, M. meretrix, etc., which were listed as Meretrix taiwanica in the past, are in fact misidentified as Meretrix taiwanica.
The Fisheries Research Institute warned that in recent years, religious groups have often purchased clams from farms in other places and released them in local areas in Taiwan. This kind of release without identifying the species and the source of the clams may lead to genetic mixing among local populations, and may even result in cross-breeding with Taiwan's native species of clams. In order to protect the precious biological resources and genetic diversity of Taiwan's native species, the introduction and propagation of clams should be conducted with caution. Moreover, the maintenance of estuarine habitats and the public's awareness of ecological conservation should be strengthened, and the correct concepts of releasing clams at the right time, in the right place, and with the right species should be established.
Figure 1. Clams grown in Taiwan are an unnamed native species of Taiwan
Figure 2. A. M. taiwanica; B. M. petechialis; C. M. lusoria
Figure 3. M. taiwanica confirmed as a new species by DNA Identification Technology
Figure 4. Geographical distribution of M. taiwanica, M. petechialis and M. lusoria