DISTRIBUTION AND ABUNDANCE OF HALOBATES SPECIES 

 (INSECTA: HETEROPTERA) IN THE EASTERN TROPICAL PACIFIC 



Lanna Chenqi and Eric Shulenberger^ 



ABSTRACT 



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//. 

 splendens, were found in the eastern tropical Pacific area. The abundance estimates (lower bounds) 

 range from 400 to 10,000 per km^. Detailed zoogeographical distributions of the four species are 

 presented. 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//, splendens, the rarest species, appears to 

 be associated with the central South Pacific watermass or the South American west coast current 

 system. 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. 



Five species of the genus Halobates Eschscholtz 

 (Insecta, Heteroptera: Gerridae), popularly called 

 marine "water striders" or "sea skaters," are 

 the only known insects whose normal habitat is 

 the high seas. These pelagic insect plankters oc- 

 cupy an unique, truly two-dimensional environ- 

 ment. They are not known to penetrate below or 

 rise above the surface (no winged forms are known 

 for any Halobates species; Cheng and Fernando 

 1969). Halobates spp. spend their entire life cycle 

 at the air-sea interface, and may therefore provide 

 us with an unique opportunity to use them as 

 biological tools for investigating air-sea and sur- 

 face phenomena. 



The peculiar habitat of oceanic Halobates spp. 

 precludes their capture (except accidentally) by 

 standard zooplankton or water-sampling equip- 

 ment, and presents interesting questions of 

 zoogeography and in the evolution of species. The 

 occasional oceanic Halobates specimens found in 

 conventional plankton samples made with sub- 

 merged nets have shown that the five oceanic 

 species are widely distributed on a scale of ocean- 

 basin magnitude (Herring 1961; Savilov 1967; 

 Scheltema 1968; Cheng 1973a, 1974). Although 

 the ranges of distribution of the Pacific //a /o6ates 



'Scripps Listitution of Oceanography, University of California, 

 La Jolla,CA 92093. 



^San Diego Natural History Museum, PO. Box 1390, San 

 Diego, CA 92112. 



Manuscript accepted February 1980. 

 FISHERY BULLETIN: VOL .78, NO. 3. 1980 



spp. have been broadly defined by Savilov ( 1967), 

 there have been few data for these insects from the 

 southeastern Pacific; furthermore, no detailed 

 quantitative study has hitherto been made on the 

 sea skaters in the Pacific Ocean. An unique series 

 of surface samples collected during the EAS- 

 TROPAC survey enabled us to carry out an exten- 

 sive study ofHalobates spp. in the eastern tropical 

 Pacific Ocean. We present here a detailed descrip- 

 tion of mesoscale (several hundreds of kilometers) 

 zoogeographic patterns of four Halobates spp. in 

 the area, as well as information on abundance, 

 cooccurrence of species, and temperature effects 

 on occurrence of species. 



Various aspects of the biology of Halobates spp. 

 are described in the literature. The taxonomy of 

 the genus is reasonably well understood (Herring 

 1961). All 42 species described are to some extent 

 associated with saltwater — mostly brackish 

 waters or nearshore marine habitats. Some are 

 confined to island groups or nearshore lagoons, 

 estuaries, or bays (Cheng 1973a; Andersen and 

 Polhemus 1976). Only five Halobates species (H. 

 micans Eschscholtz, H. sericeus Eschscholtz, H. 

 sobrinus White, H. splendens Witlaczil, and H. 

 germanus White) are truly high-seas animals. 

 Special adaptations of pelagic Halobates to its 

 peculiar habitat include: 1) an ability to lay eggs 

 on flotsam (Cheng 1974); 2) a cuticle with a mi- 

 crohair layer which traps air and prevents the 



579^^ 



