Riparian deforestation is a significant threat to freshwater riverine ecosystems and sensitive fauna that depend on clean water. Sensitive aquatic species are vulnerable to the destruction of riparian forest cover which diminishes protection from pollutants, sedimentation, and solar radiation, while also depleting dissolved oxygen. In this thesis, I explore the influence of degraded riparian forest cover and its effect on dissolved oxygen on the embryonic viability of a sensitive freshwater habitat specialist, the Eastern hellbender.
Hellbenders are a large-bodied, long-lived amphibian that inhabits fast flowing, cold mountain streams in the eastern United States. Over the last several decades, hellbender populations have experienced declines that are associated with low riparian forest cover, a geriatric population age structure, and high rates of nest failure. Adult male hellbenders normally provide extensive paternal care to embryos and larvae over an 8-month period. However, researchers have recently discovered that in degraded populations, hellbender nests are failing due to whole-clutch filial cannibalism by adult males. The underlying mechanism that triggers males to eat their young remains unknown, but one possibility is that eggs are not developing properly and as a result the attending male ceases to provide care. However, the embryonic viability of clutches developing in habitats with low riparian forest cover is unknown.
Given the limited research on hellbender embryonic viability, I first sought to examine whether embryo viability is associated with a forest cover gradient. To accomplish this, I inherited two years of laboratory and field data, and I conducted a final third year of data collection for the study. Over these three years of data collection, I simultaneously evaluated embryo viability in a controlled captive rearing system while classifying nest failure due to whole-clutch cannibalism of sibling embryos in the field. I found significantly lower hellbender embryo viability, faster hatching times, and higher rates of underdeveloped hatchlings in hellbender populations with degraded riparian forest cover. However, I found no relationship between embryonic viability and whole-clutch filial cannibalism. I concluded that elevated specific conductance of water (i.e., dissolved ions) associated with loss of forest cover may affect the embryonic development of hellbenders, but this hypothesis has yet to be tested.
To further explore the impact of degraded riparian forest cover on hellbender embryonic viability, I designed a study to evaluate the influence of depleted dissolved oxygen on embryonic development. To accomplish this, I designed and implemented a dissolved oxygen manipulation system to rear sibling embryos in high, medium, and low dissolved oxygen concentrations. I found that hellbender embryos are vulnerable to relatively modest reductions in dissolved oxygen (i.e., 5 mg/L), comparable to those found to affect embryos of some of the most sensitive species examined to date. Nests reared in low dissolved oxygen had a lower percentage of viable hatchlings, lower hatching success, higher rates of underdeveloped hatchlings, and smaller morphometrics compared to those reared at higher dissolved oxygen concentrations. I concluded that hellbenders may be particularly susceptible to reductions in dissolved oxygen because of their high degree of specialization for well oxygenated streams, and I suggest prioritizing additional research on dissolved oxygen to advance hellbender conservation.
Taken together, my research established a foundation of knowledge on the sensitivities of hellbender embryos to degraded water quality caused by low riparian forest cover. Further, my work underscored the importance of riparian forest conservation for hellbender populations and for other freshwater biodiversity. Protection of riparian forest will also be critical to build resilience in streams against the existential threat of climate change. / Master of Science / Deforestation along rivers is a significant threat to freshwater systems and sensitive animals that depend on clean water. Sensitive river species are vulnerable to the destruction of forest cover which removes protection from pollutants, run off, sun light, and exposes them to low dissolved oxygen—the amount of oxygen in the water, which is necessary for the survival of aquatic animals. In this thesis, I explore how low forest cover may impact egg quality of a sensitive freshwater animal, the eastern hellbender salamander.
Hellbenders are a large-bodied, long-lived amphibian that lives in fast-moving, cold mountain streams in the eastern United States. Over the last several decades, hellbender numbers have rapidly declined. These declines are associated with low forest cover along streams, elderly populations, and unsuccessful nests. Adult male hellbenders normally provide care to their eggs and hatchlings for about eight months after the eggs are laid. Researchers have recently found that in streams where hellbender numbers are declining, hellbender nests are not successful because adult males are eating their eggs before the eggs can hatch. Researchers know that low forest cover triggers hellbender fathers to cannibalize their eggs, but the mechanism by which forest cover causes this trigger is unknown. Unsuccessful nests due to cannibalistic fathers in declining populations suggest that hellbender eggs might be unhealthy, making it more profitable to eat them than to care for them. However, the health of eggs in water from low forest cover is unknown and an important knowledge gap to fill to uncover what is triggering cannibalism in low forest cover populations.
Given the limited research on hellbender egg health, I first sought to examine whether egg health is associated with changes in forest cover. To do this, I received two years of laboratory and field data, and I conducted a final third year of data collection for the project. Over these three years of data collection, I determined egg health by raising eggs in their own site water in the lab and simultaneously determined whether siblings in the field were eaten by their dads. I found lower hellbender egg health, shorter time to hatch, and more premature hatchlings in hellbender populations with low forest cover. However, I found no relationship between egg health and whether hellbender dads ate their eggs. I concluded that poor water quality associated with loss of forest cover may affect the health of hellbender eggs, but this has not been tested yet.
To further explore the impact of low forest cover on hellbender egg health, I designed a study to determine the influence of low dissolved oxygen on egg health and growth. To do this, I designed and implemented a dissolved oxygen experiment to raise sibling eggs in high, medium, and low dissolved oxygen levels. I found that hellbender eggs are vulnerable to relatively moderate levels of reduced oxygen (i.e., 5 mg/l), which is comparable to how other highly sensitive species react. Nests raised in low dissolved oxygen had a lower number of healthy hatchlings, lower number of eggs that hatched, higher numbers of premature hatchlings, and smaller sizes compared to those raised in higher dissolved oxygen levels. I concluded that hellbenders may be particularly vulnerable to low dissolved oxygen because they have adapted to live in well oxygenated streams, and I emphasize the importance of studying dissolved oxygen to inform hellbender conservation.
Taken together, my research created a foundation of knowledge on the vulnerabilities of hellbender eggs to poor water quality because of low forest cover. Filling these knowledge gaps is important, because it informs policy makers and managers on how to best protect hellbenders and other stream animals from declining. Further, my work emphasized the importance of forest conservation for hellbenders and for other sensitive freshwater animals. Forested streams will also be important to build protection against other human disturbances, such as climate change.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/123630 |
| Date | 18 November 2024 |
| Creators | Funkhouser, Holly Ann |
| Contributors | Fish and Wildlife Conservation, Hopkins, William A., Hotchkiss, Erin R., Mims, Meryl C. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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