Distribution limits of the geoduck clams panopea generosa and p. globosa on the pacific coast of Mexico

Two species of geoduck clams, Panopea, are known from the Pacific coast of Mexico: P. generosa, also present in the temperate areas along the western coast of North America, and P. globosa, originally considered endemic to the Gulf of California. Often regarded as a temperate and a tropical species, their respective distributions were assumed to be clearly separate. However, commercial interests recently found populations in the temperate-tropical transition zone, thus raising doubts regarding their taxonomic identity and the distribution limits of each species. Discriminant function analysis was used to examine the morphological characteristics of the shells of individuals from nine locations to identify their species and to re-examine the distribution limits of Panopea spp. in this region. Results show that the tropical limit in the distribution of P. generosa is the western coast of the Baja California Peninsula, south to at least Punta Canoas (29°43′N). It was found that the distribution of P. globosa not only includes the Gulf of California but extends to at least Bahía Magdalena (24°38′N) on the western coast of the peninsula. This is the first report of P. globosa outside of the Gulf of California, thus extending its distribution to more temperate areas.