# Euryhaline Atlantic stingray (Hypanus sabinus) exhibit elevated oxygen supply capacity in hyposaline water: implications for estuarine species resilience and conservation

## TL;DR

Atlantic stingrays can better handle low oxygen levels in low-salinity water, which helps them survive in changing estuarine environments.

## Contribution

This study reveals a novel physiological adaptation in euryhaline elasmobranchs to fluctuating salinity and oxygen levels.

## Key findings

- Oxygen supply capacity increased by 20% in low salinity conditions.
- Critical oxygen pressure decreased by 30% in hyposaline water.
- Atlantic stingrays show enhanced hypoxia tolerance in low salinity environments.

## Abstract

Estuarine environments are characterized by fluctuating abiotic conditions, such as salinity and oxygen partial pressure, which challenge the physiological systems of resident species. Organisms inhabiting these systems have evolved physiological plasticity to cope with this variability, particularly in relation to oxygen availability. Estuarine species tend to exhibit greater hypoxia tolerance compared to coastal marine species, likely due to periodic low oxygen exposure. However, the effects of salinity fluctuations on oxygen transport remains unclear. This study investigated the effects of different salinity levels on the oxygen supply capacity of the Atlantic stingray (Hypanus sabinus), a euryhaline elasmobranch in the temperate west Atlantic and Gulf of Mexico. Maximum metabolic rates and oxygen supply capacity were measured at high, medium and low salinities (32, 16 and 6 psu, respectively). Critical oxygen pressure (PcMax), where maximum metabolism and aerobic scope become oxygen limited, was also calculated. Results showed a significant 20% increase in oxygen supply capacity and a 30% decrease in PcMax under low salinity compared to high salinity. These findings suggest that Atlantic stingrays improve their oxygen supply capacity and are more hypoxia tolerant in hyposaline conditions. Enhanced oxygen supply capacity may represent an adaptive strategy, enabling Atlantic stingrays to maintain metabolic performance in low oxygen environments. This study provides novel insight into the adaptive capacity of euryhaline elasmobranchs to balance oxygen transport and metabolic function across salinity gradients. It highlights the importance of physiological plasticity in estuarine species’ responses to climate-driven changes in salinity and oxygen availability. These findings can inform management strategies by identifying species with greater resilience to hypoxia and salinity shifts, supporting more effective conservation efforts under future climate scenarios.