Morphological and genetic variations of Meretrix spp. (Bivalvia: Veneridae) recently distributed in the coastal waters of the Gulf of Thailand

Asian hard clams, Meretrix spp., are found in the coastal waters of the Indo-Pacific region, including Thailand. Climate change is a widespread and escalating global threat to biodiversity and ecosystems. This study aims to examine the current distribution of Meretrix in the Gulf of Thailand. Morphometric and genetic analyses were used for species identification and to understand intra- and interspecies shell variations of for all species we encountered. A genetic and morphometric study revealed the presence of two species of Meretrix. Meretrix meretrix was not found in the lower Gulf of Thailand, while M. astricta was not found in the eastern Gulf of Thailand. This is the first reporting of M. astricta in Thailand since 2010. Three and four genetic haplotypes were revealed for M. meretrix and M. astricta, respectively. The genetic distance within species ranged from 0.002 to 0.007 and 0.002–0.021 in M. meretrix and M. astricta, respectively. The BLAST results for M. astricta sequences showed over a 24% difference compared to related Meretrix species, while our M. meretrix sequences showed a high percentage of similarity with some M. meretrix sequences in the database. This study provides evidence of a recent decline in the species number of Meretrix in the Gulf of Thailand, which is part of the Pacific Ocean region. Species distributions and changes in community composition should be taken into account for management practices to ensure the sustainability of their ecosystems.