# Influence of Hypoxia, Dehydration and Salinity on Survival of Orthohalarachne Marine Mite Larvae: Limits to Dispersion

## TL;DR

This study explores how low oxygen, dehydration, and salinity affect the survival of two marine mite larvae species, revealing that humidity is the main challenge during their dispersal.

## Contribution

The study provides new insights into the ecophysiological adaptations of marine mite larvae to environmental stress during dispersal.

## Key findings

- Both mite species are highly tolerant to hypoxia but show low survival in direct air.
- O. attenuata is less tolerant to hyperosmotic conditions than O. diminuata.
- Humidity is the primary limiting factor for larval survival and dispersal.

## Abstract

The present study examines the responses of O. attenuata and O. diminuata mite larvae from A. australis to low oxygen levels and conditions of humidity and salinity. The objective of this study was to ascertain the impact of environmental factors on survival of mite larvae within the nasal cavity during their development and outside the host during dispersal. We found that both species have high resistance to oxygen deprivation, and that humidity is the primary limiting factor outside the host. Also, both species show different rates of survival under stressful salinity conditions, with O. attenuata less tolerant than O. diminuata. In conclusion, O. attenuata and O. diminuata larvae have physiological capabilities to tolerate environmental stresses both inside and outside the host, suggesting ecophysiological adaptations relevant to their parasitic lifestyle.

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.