DNA Barcoding Analysis of Meretrix Clams (Bivalvia: Veneridae) Around Hainan Island, China

This study aimed to assess the species diversity and genetic structure of Meretrix clams around Hainan Island using mitochondrial cytochrome c oxidase subunit I (COI) DNA barcoding. The genus Meretrix is a common and economically important group of bivalves in the intertidal zones of Hainan Island, widely distributed in estuarine and nearshore sandy habitats and playing a significant role in local fisheries and aquaculture. In recent years, studies on Meretrix in Hainan have mainly focused on morphological identification and species records from limited coastal areas; however, due to the high phenotypic plasticity of shell morphology and the relatively subtle differences among species, traditional morphology-based identification remains challenging. Meanwhile, molecular systematic investigations of Meretrix in Hainan are still limited, particularly systematic studies using DNA barcoding to assess species diversity and geographic distribution patterns. A total of 141 individuals were collected from ten intertidal sites. Four species were identified—M. lyrata, M. lamarckii, M. meretrix and M. petechialis—with interspecific genetic distances (17.6–22.7%) far exceeding intraspecific variation (0.3–0.9%). Phylogenetic analysis based on COI sequences clearly distinguished four Meretrix species from the waters around Hainan Island, with each species forming a well-supported monophyletic clade, supporting their status as independent evolutionary lineages. In addition, two markedly divergent genetic lineages were detected within M. petechialis, suggesting that this species may possess a relatively complex population structure, one of which is typically found in northern Chinese waters, suggesting possible human-mediated introduction. Species richness was higher on the eastern coast, potentially influenced by regional hydrodynamic conditions. This study provides baseline DNA barcode data for Meretrix species in Hainan and supports the need for integrative management of this economically important resource.