Morphological characters for practical identification of the copepodite stages of three sympatric Calanus species in the western North Pacific, with concurrent application of species-specific PCR

Abstract

Morphological characters for distinguishing among Calanus sinicus, C. jashnovi and C. pacificus are described for all copepodite stages using specimens collected from the western North Pacific. We applied species-specific polymerase chain reaction (PCR) to identify the three species. The three species differ morphologically either in (i) prosome length (PL), (ii) length and width of caudal ramus, or (iii) shape and width of cephalosome. At copepodite stages IIIVI female (CIIICVI female), PLs of C. jashnovi were greater than those of both in C. sinicus and C. pacificus. At CIII, PL of C. jashnovi slightly overlapped with that of C. sinicus, but C. jashnovi also differed from the other species in caudal ramus length (CRL) and width (CRW). CIIICVI females of C. sinicus and C. pacificus differed in CRL. At CICII, the C. sinicus cephalosome was oval-shaped, with a minor axis longer than that of C. pacificus, whereas C. jashnovi had a rhomboid rather than oval cephalosome. Species composition of Calanus copepodites was investigated at a location in the OyashioKuroshio mixed region using the aforementioned morphological characters. Copepodites of C. sinicus were the most abundant of the three species in the region. © 2011 The Author.