Observations on depth distribution, diversity and abundance of pelagic nemerteans from the Pacific Ocean off California and Hawaii

Meso- and bathypelagic nemerteans were collected during five cruises west of Pt. Conception, California, and one west of Oahu, Hawaii, from depths of 0–3800 m, using a 10 m2 Tucker Trawl modified with a thermally protected closing cod end, as well as MOCNESS-10 and MOCNESS-1D trawls. In this study, about 53 putative species were collected off California and about 23 off Hawaii, with little taxonomic overlap between the two groups, as compared to 16 and 0 species previously known from these regions. Numbers of nemertean individuals and species were greatest between 625 and 1750 m off California, and 1300–2500 m off Hawaii. Abundance of nemerteans off California was about 10 times that off Hawaii. The Shannon– Wiener diversity index (H′) was higher for Hawaii than for California due to numerical dominance by two species, Phallonemertes cf murrayi and Nectonemertes cf mirabilis, off California and a more even species distribution off Hawaii. Neither of the two dominant California species showed evidence of nocturnal vertical migration to shallow water. This is the first report of a Phallonemertes species from the Pacific and the first report of pelagic nemerteans from waters off Hawaii.