Marine Biology Research Division

Halobates specimens were sorted from 1,649 surface neuston samples collected from the eastern tropical Pacific Ocean. At least one specimen was captured in each of 498 samples. Only 34 samples contained more than one species of Halobates. Four species, H. micans, H. sobrinus, H. sericeus, and H. splendens, were found in the eastern tropical Pacific area. The abundance estimates (lower bounds) range from 400 to 10,000 per km² . Detailed zoogeographical distributions of the four species arepresented. Halobates micans is a warmwater cosmopolite found between lat. 20° N and 20° S; H. sericeus appears to be confined to the central watermasses of the North and South Pacific and does not occur in the zonal equatorial currents; H. sobrinus, the most abundant of the four, is confined to the equatorial upwelling regions off the west coast of Central America; and H. splendens, the rarest species, appears to be associated with the central South Pacific watermass or the South American west coast currentsystem. Although there is considerable overlap in the absolute geographical ranges of the three more abundant species, the regions in which they are abundant are almost entirely separate. Whether this is due to biological or physical processes is unknown.