DISTRIBUTION AND RELATIVE ABUNDANCE OF PSEUDOCALANUS-MOULTONI AND P-NEWMANI (COPEPODA, CALANOIDA) ON GEORGES BANK USING MOLECULAR-IDENTIFICATION OF SIBLING SPECIES

The sibling species, Pseudocalanus moultoni (Frost, 1989) and P. newma ni (Frost, 1989), occur sympatrically on Georges Bank. Taxonomic discr imination of the species relies on subtle morphological characteristic s, making routine identification of the species very difficult. DNA se quence variation of two mitochondrial genes, 16S rRNA and cytochrome o xidase I (COI), reliably discriminated P. moultoni and P. newmani. Lev els of DNA sequence variation for both genes were consistent with thos e between species of calanoid copepods. A molecular systematic protoco l (based on allele-specific PCR amplification) was designed from the C OI sequences and used to discriminate females of the two species. The distributions and relative abundances of the two species were mapped f or April 1996 based on samples of 15 to 30 females from 12 collections across Georges Bank. The results of this study indicated that P. moul toni females predominated along the northern flank of Georges Bank, wh ile P. newmani females were common on the southern flank, deeper than the 60-m isobath.