Abstract
Sea-level rise, drought and water diversion can all lead to rapid salinization of freshwater habitats, especially in coastal areas. Increased water salinities can in turn alter the geographic distribution and ecology of freshwater species including turtles. The physiological consequences of salinization for freshwater turtles, however, are poorly known. Here, we compared the osmoregulatory response of two geographically separate populations of the freshwater Western Pond Turtle (Actinemys marmorata)-a species declining across its range in western North America-to three constant salinities: 0.4ppt, 10ppt and 15ppt over 2weeks. We found that turtles from a coastal estuarine marsh population regulated their plasma osmolality at lower levels than their conspecifics from an inland freshwater creek population 45km away. Plasma osmolalities were consistently lower in estuarine marsh turtles than the freshwater creek turtles over the entire 2-week exposure to 10ppt and 15ppt water. Furthermore, estuarine marsh turtles maintained plasma osmolalities within 1 SD of their mean field osmolalities over the 2-week exposure, whereas freshwater creek turtles exceeded their field values within the first few days after exposure to elevated salinities. However, individuals from both populations exhibited body mass loss in 15ppt water, with significantly greater loss in estuarine turtles. We speculate that the greater ability to osmoregulate by the estuarine marsh turtles may be explained by their reduced feeding and drinking in elevated salinities that was not exhibited by the freshwater creek population. However, due to mass loss in both populations, physiological and behavioural responses exhibited by estuarine marsh turtles may only be effective adaptations for short-term exposures to elevated salinities, such as those from tides and when traversing saline habitats, and are unlikely to be effective for long-term exposure to elevated salinity as is expected under sea-level rise.
Highlights
Freshwater ecosystems deliver some of the most important goods and services to wildlife, fish, plants and humans around the world (Costanza et al, 1997; Wilson and Carpenter, 1999)
Due to mass loss in both populations, physiological and behavioural responses exhibited by estuarine marsh turtles may only be effective adaptations for short-term exposures to elevated salinities, such as those from tides and when traversing saline habitats, and are unlikely to be effective for long-term exposure to elevated salinity as is expected under sea-level rise
Estuarine marsh turtles had higher baseline field osmolalities when captured than did the freshwater creek turtles (291.6 ± 2.8 versus 268.6 ± 1.7 mmol/kg, respectively; P < 0.001), and males had higher osmolalities compared to females (286.6 ± 2.9 versus 271.6 ± 3.1 mmol/kg, respectively; P < 0.001) (Fig. 3)
Summary
Freshwater ecosystems deliver some of the most important goods and services to wildlife, fish, plants and humans around the world (Costanza et al, 1997; Wilson and Carpenter, 1999). Despite their importance to ecosystem function, these systems are increasingly at risk of salinization due to land conversion, agriculture and freshwater diversion (Naiman and Turner, 2000). Drought and sea-level rise have further reduced water quality by increasing water temperatures and salinities, in the Central Valley and coastal regions of California (Cardona et al, 2004; Escriva-Bou et al, 2017). Past sea-level increases—20 cm in the last 100 years— coupled with future projections — 0.74 m to 1.37 m by 2100 (Ackerly et al, 2018)—suggest a continuing trend of increasing mean water salinity across the San Francisco Bay Estuary (SFBE; Cayan et al, 2008a, 2008b; Cloern et al, 2011)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
