Orthohalarachne attenuata and O. diminuata mites are parasites of the respiratory system of Pinnipeds. During hosts’ dives, mites must cope with changing conditions of oxygen availability in the nasal cavity. Adults and nymphs live inside the host, but larvae are active and responsible for colonizing new hosts. Hence, larvae are also exposed to environmental conditions with variable temperature and pressure, as well as to dehydration and changes in salinity. Although both species live within the respiratory tract of hosts, adults attach to different sections. Also, larvae have differential thermal tolerances and locomotion capacities. In this study, we show the effect of hypoxia, humidity and salinity on survival of O. attenuata and O. diminuata mite larvae. We found that both species are highly tolerant to hypoxia and can withstand it for long periods. In turn, both species showed low survival when exposed to direct air. Finally, hyperosmotic solution was highly harmful for O. attenuata, but not for O. diminuata. Our results show that humidity rather than oxygen availability is a constraint for survival and a limitation for dispersal when searching for new hosts. The present study expands our knowledge of ecophysiology and adaptations to changing conditions experienced during the dispersal of these marine parasite species.

Orthohalarachne attenuata and O. diminuata mites are parasites of the respiratory system of pinnipeds. During hosts dives, mites are challenged to cope with changing conditions of available oxygen in the nasal cavity. Adults and nymphs live inside the host but larvae are active and responsible for colonizing new hosts. Hence, larvae are also exposed to environmental conditions with variable temperatures, dehydration or changes in salinity. In this study, we studied the effect of hypoxia, humidity and salinity on survival of mite larvae in O. attenuata and O. diminuata. We found that both species are highly tolerant to withstand long times under hypoxia. In turn, both species showed low survival when exposed to direct air. Finally, the hyperosmotic solution was highly harmful for O. attenuata compared to O. diminuata. Our results show that humidity rather than oxygen availability is a constraint for survival and a limitation for dispersal when searching for new hosts. The present study expands our knowledge of ecophysiology and adaptations to changing conditions experienced during the dispersal of these marine parasite species.