Marine Biology Research Division

Despite the remarkable evolutionary success of insects at colonizing every conceivable terrestrial and aquatic habitat, only five Halobates (Heteroptera: Gerridae) species (~0.0001% of all known insect species) have succeeded at colonizing the open ocean – the largest biome on Earth. This remarkable evolutionary achievement likely required unique adaptations for them to survive and thrive in the challenging oceanic environment. For the first time, we explore the morphology and behavior of an open-ocean Halobates germanus and a related coastal species H. hayanus to understand mechanisms of these adaptations. We provide direct experimental evidence based on high-speed videos which reveal that Halobates exploit their specialized and self-groomed body hair to achieve extreme water repellence, which facilitates rapid skating and plastron respiration under water. Moreover, the grooming behavior and presence of cuticular wax aids in the maintenance of superhydrophobicity. Further, reductions of their body mass and size enable them to achieve impressive accelerations (~400 ms⁻²) and reaction times (~12 ms) to escape approaching predators or environmental threats and are crucial to their survival under harsh marine conditions. These findings might also inspire rational strategies for developing liquid-repellent surfaces for drag reduction, water desalination, and preventing bio-fouling.

We document the discovery of a unique flightless marine midge Pontomyia (Chironomidae) in the Indian Ocean, presenting descriptions and photographs of the insect and its environment at Christmas Island, Australia. The insect is identified as P. natans, with distinctive male genitalia and rudimentary claws on the hind legs. This species is widely distributed in the Pacific Ocean but the only previous record from the Indian Ocean was from the Maldives. It is highly likely that other populations are present along the continental coast of the latter ocean basin.

The question of how many marine species exist is important because it provides a metric for how much we do and do not know about life in the oceans. We have compiled the first register of the marine species of the world and used this baseline to estimate how many more species, partitioned among all major eukaryotic groups, may be discovered.

Plastic pollution in the form of small particles (diameter less than 5 mm)—termed ‘microplastic’— has been observed in many parts of the world ocean. They are known to interact with biota on the individual level, e.g. through ingestion, but their population-level impacts are largely unknown. One potential mechanism for microplastic-induced alteration of pelagic ecosystems is through the introduction of hard-substrate habitat to ecosystems where it is naturally rare. Here, we show that microplastic concentrations in the North Pacific Subtropical Gyre (NPSG) have increased by two orders of magnitude in the past four decades, and that this increase has released the pelagic insect Halobates sericeus from substrate limitation for oviposition. High concentrations of microplastic in the NPSG resulted in a positive correlation between H. sericeus and microplastic, and an overall increase in H. sericeus egg densities. Predation on H. sericeus eggs and recent hatchlings may facilitate the transfer of energy between pelagic and substrate-associated assemblages. The dynamics of hard-substrate-associated organisms may be important to understanding the ecological impacts of oceanic microplastic pollution.

Among millions of insect species known in the world only five species of Halobates (Heteroptera: Gerridae) are able to live in the high seas. The general public is probably not aware that there are insects living on the open ocean and even most marine scientists have never seen a live or preserved specimen with their own eyes. The genus Halobates was first collected during a Russian oceanographic expedition around the world between 1815 and 1818.

We analyzed the foraging ecology of seabirds in the eastern tropical Pacific Ocean during 1983–1991 on a series of oceanographic cruises during spring and fall of each year. We report details about the consumption of sea skaters Halobates spp., marine insects that are small, can hide well within sea foam, and can be very fast moving. One abundant sea skater of the four species present in the study area, H. sobrinus, is not taken by sea birds, and the reason is unknown. Among the predators, it appears that frigate storm-petrels, White-faced Storm-Petrel Pelagodroma marina and White-bellied Storm-Petrel Fregetta grallaria (likely also White-throated Storm-Petrel Nesofregetta fuliginosa), make directed efforts to consume sea skaters, a fact that may explain their unique flight and foraging behavior: slow, with extensive “kicksplashing” against the sea surface, to incite movement in Halobates. The few other seabirds for which sea skaters constitute more than an incidental component of the diet (Herald Petrel Pterodroma heraldica, Bulwer’s Petrel Bulweria bulwerii) also move slowly across and close to the sea surface. In the case of the White Tern Gygis alba, it readily hovers, an ability that would be advantageous to taking these insects. Among the avian species that rarely take a sea skater, almost all are included in the guild of seabirds that associate with tuna, and as a result they must fly quickly to keep pace.

Two species of ocean skaters, Halobates germanus and Halobates micans, live in the tropical and subtropicalwaters of the Indian Ocean. From December 1992 to December 1993, Halobates was intensively sampledin the easternmost region of the South Indian Ocean (13–18.5°S, 114–121E°), from which there have been a small number of records of Halobates. No H. germanus was caught, but a total of 1190 H. micans were collected, with densities estimated at 13 900–28 100 individuals/km2. This suggests that H. micans lives in the study area at high densities comparable to those in the Atlantic and the Pacific Oceans. We also discuss the possible effects of ocean currents and winds on the geographic distributions of the two Halobates speciesin the eastern South Indian Ocean.

Eighty five species of aquatic and semi-aquatic Heteroptera belonging to 14 families are reported from Xishuangbanna and nearby counties in Yunnan. Collecting locations and habitats are given. Ten species (Hydrometra jaczewskii, H. longicapitis, H. orientalis, Amemboa (Amemboa) sexualis, A. (A.) lyra, Metrocoris ciliatus, Pleciobates pacholatkoi, Ptilomera burmana, Rhyacobates anderseni, Ventidus pulai) are new records for China. In addition, Nine new species (Timasius yunanensis, Ranatra lansburyi, R. sterea, Micronecta (Micronecta) erythra, M. (M.) janssoni, M. (M.) lobata, M. (M.) ornitheia, M. (Unguinecta) melanochroa, Anisops pseudostali) based on material collected during this study, have been described and published elsewhere.

Among the million or so insect species known, only a few thousand are found in marine habitats. The genus Halobatesis almost exclusively marine and is unique in having the only known species to live in the open ocean. Of the 46 Halobatesspecies described, only five are completelyoceanic in habitat, with the majority of species living in coastal areas associated with mangroves or other marine plants. This review presents a brief historical account of the genus and providesinformation on various aspects of its life history, ecology, special adaptations, distribution, and biogeography. Distribution maps of the five oceanic species as well as several of the more widely distributed coastal species have been updated. The phylogeny and evolution of Halobatesbased on morphology and recent molecular data are also discussed. A key to all known species of Halobatesand related genera and a checklist of all species and their distributions are included as appendices.