Skaters of the seas - comparative ecology of nearshore and pelagic Halobates species (Hemiptera: Gerridae), with special reference to Japanese species

The insects overwhelm all other organisms of the world in species numbers and diversity. However, there are relatively few insects that inhabit the sea. Most of them are confined to the intertidal zone, with only five species of sea skaters, genus Halobates, having been successful in colonizing the open ocean. We discuss the ecology of both coastal and pelagic Halobates and the closely related genus Asclepios, focusing on their distribution ranges and adaptive strategies to marine environments accompanied by brief discussions of their biology. Updated information on the known localities for three species of Asclepios and some 40 coastal species of Halobates are presented. Many species live in vulnerable coastal habitats exposed to environmental pollution and coastal development. As a case study we trace the historical changes in populations of three Japanese sea skaters, Asclepios shiranui, Halobates matsumurai and H. japonicus, all designated as endangered species. For oceanic Halobates, we present an updated distribution map along with global current systems and sea-surface temperatures, examine interactions between distribution ranges and physical factors at the air-sea interface and discuss spatio-temporal variations in populations of each species. Finally, we infer the life history strategy of oceanic Halobates through theoretical considerations.