Supercooling points and heat coma temperatures in four species of oceanic sea skaters of the genus Halobates (Heteroptera: Gerridae: Halobatinae)

Abstract The only insects known to live in the open ocean are several species of sea skaters of the genus Halobates (Heteroptera: Gerridae). We have collected four species in the tropical western Pacific Ocean and measured heat coma temperature (HCT) and supercooling point (SCP) in 132 specimens. The SCPs were relatively low (ranging between − 18 °C and − 19 °C) and similar in all species. Significant inter-species differences were found in the level of HCT. The lowest HCT 32.9 °C was found in Halobates micans Eschscholtz, 1822, which is distributed in thermally stable tropical waters. The highest HCT levels of 36.6 °C and 36.0 °C were observed in Halobates sericeus Eschscholtz and Halobates germanus White, 1883, respectively, mostly occurring in thermally more fluctuating habitats (subtropical and warm temperate waters, and coastal waters, respectively). A new species, H . sp . (under process of description) showed an intermediate HCT of 34.8 °C. In addition, we found significant negative statistical correlation between HCT and SCP values at the species and individual levels. We discuss our results in the light of putative relationship between thermal physiology of sea skaters and their distribution.