A Review of the Effects of Freshwater Habitat Quality on Aquatic & Semi-Aquatic Turtles

Freshwater turtles and terrapins require an aquatic habitat as part of their natural ecology. The health of these habitats—the quality of the water, which can be affected by natural phenomena as well as pollution and human alterations of the watershed's natural flow—are inextricably intertwined with the persistence of the turtle species that rely on them. However, likely because of the vast number of species, habitats, and aquatic variables involved, a comprehensive review of the relationship between freshwater turtles and their aquatic environments has yet to be conducted. Here, we break down freshwater habitat quality into discreet natural and anthropogenic variables and summarize their impacts on the physical, behavioral, and population responses of freshwater turtles. We found that among natural variables, salinity and temperature were the most studied, while heavy metals received the most attention among the anthropogenic pollutants. Much of this research measured contaminant concentrations in turtle tissues, blood, or claws to assess their value as environmental biomonitors, rather than directly evaluating short- or long-term health effects. Meanwhile, the impacts of many other natural water quality metrics such as pH, turbidity, and contaminants like coal and oil spills remain severely under-studied. Taxonomic coverage was similarly biased towards a small number of common species, despite many threatened species being especially vulnerable to habitat degradation. By drawing attention to these gaps and biases, we hope to make the path clearer for future research to identify the impacts of habitat quality metrics on the health and distribution of freshwater turtles.