# Hydroelectric Dam May Impact the Microbiome of an Endangered Northern Map Turtle (Graptemys geographica) Population

## TL;DR

A hydroelectric dam may be altering the gut and oral bacteria of endangered Northern Map Turtles, potentially affecting their health.

## Contribution

This study is among the first to link dam impacts to microbiome changes in an endangered reptile species.

## Key findings

- The Conowingo Dam significantly influences the structure of Northern Map Turtle cloacal and oral microbiomes.
- Bacteria linked to pollution and disease, such as Acinetobacter and Aeromonas, are more prevalent above the dam.
- No significant microbiome differences were found between male and female turtles despite dietary differences.

## Abstract

Classified as state-endangered, Maryland’s population of Northern Map Turtles (NMTs) (Graptemys geographica) faces habitat alteration and fragmentation due to the Conowingo Hydroelectric Dam and other factors. Maryland’s NMTs also reside in an urbanized area with high levels of human activity, which leads to overall disturbance and pollution. The combined impacts of these stressors could be affecting the health of NMTs and may contribute to future decline. The microbiome has been explored as an indicator of organismal health in other species and can be used to inform wildlife management strategies. We collected cloacal (n = 35) and oral (n = 34) microbiome swabs from wild NMTs at four different sites along the Maryland portion of the Susquehanna River in 2022. Using 16 S rRNA sequencing, results suggested that the dam plays a significant role in determining cloacal and oral microbiome structure, with bacteria associated with pollution and disease being significantly more prevalent above the dam. Of note are Acinetobacter spp., which is associated with heavy metal contamination, and Aeromonas spp., which is associated with shell disease in map turtles. Despite the known dietary dimorphism of NMTs, we did not find significant differences in the microbiomes of males and females. The impact that dams have on microbiomes and wildlife is not well understood, and these results may help to enact more specific management strategies in these systems. Our findings will contribute to the conservation of an endangered freshwater turtle population while adding to the limited breadth of knowledge of reptilian health.

The online version contains supplementary material available at 10.1007/s00284-026-04846-w.