Lowered salinity tolerance in sea skaters Halobates micans, Halobates sericeus, and Halobates sp. (Heteroptera:...

Adult specimens of three species of oceanic sea skater, Halobates sericeus Eschscholtz, Halobates micans Eschscholtz, and Halobates sp. were placed in one of four solutions of different salinity (sea water [35-36‰], sea water : fresh water = 2:1 [23-24‰], sea water : fresh water = 1:2 [11-13‰], and fresh water [0‰]) after collection from the temperate and subtropical Pacific Ocean, tropical Indian Ocean, and Tomini Gulf in Indonesia, and observed in 2-h intervals until they died. H. micans collected from the tropical Indian Ocean survived twice a long (80-100 h) on average as H. sericeus collected from the temperate and subtropical Pacific Ocean (35-45 h) under salinities of 12-36‰. Paralysis from freshwater treatment occurred within 2-9 h in all specimens of both species of H. sericeus from the Pacific Ocean and H. micans from the Indian Ocean, and all insects died within 2 hr of starting the paralysis. In fresh water, oceanic sea skaters of H. sp. collected from the inner water of Tomini Gulf survived for ≍24 h on average, significantly longer than those collected from the open ocean. Significantly longer length of survival was shown by the three species on one-thirds, two-thirds brackish, and 100‰ sea water than on fresh water. The long length of survival shown by oceanic sea skaters even in brackish water may be an adaptation to the occasional rain fall on the sea water film.