Annually, it is estimated that 82 million tons of global plastic waste is either mismanaged or littered, bypassing waste management practices. This mismanagement causes the permeation of plastic debris into the environment, which then undergoes natural degradation processes. These degradation processes result in the proliferation of miniscule plastic particles known as microplastics. Due to the inherent proximity to sources of anthropogenic waste, concerns of microplastic pollution and its impact on freshwater ecosystems have recently increased. Until recently, microplastic research has primarily been focused on the toxicological affects felt by an individual organism rather than the intricate interactions that occur between taxa. Only focusing on the individual toxicological impact turns a blind eye on the communities that maintain ecosystem health and stability. To that end, our experiment was unique as it will be the first study assessing the impact of a freshwater symbiosis, as symbioses in the scope of toxicokinetic studies have primarily been dominated by that of terrestrial and marine relationships. This knowledge gap is a serious concern as its argued freshwater systems are more contaminated, than that of other aquatic habitats. To address this knowledge gap, we conducted mesocosm-based exposure-response assays, exposing the crayfish-branchiobdellidan symbiosis to microplastics of fibrous, microsphere, and tire wear particle morphologies while varying symbiont densities. We used the crayfish-branchiobdellidan model system in our study due to its amenability to laboratory monitoring and manipulation. The crayfish C. appalachiensis, common in the Virginia New River Basin, served as hosts to obligate ectosymbiotic annelids in the order Branchiobdellida. Previous research, using the crayfish-branchiobdellidan symbiosis demonstrated that the interaction is a cleaning symbiosis, where hosts benefit from reduced gill fouling while symbionts benefit from increased resource availability. We observed the physical and behavioral changes of the crayfish-branchiobdellidan symbiosis over a 172-day chronic exposure assay. Our results show, crayfish hosts with higher symbiont densities experienced decreased physical growth when exposed to microplastics compared to the control. This alteration in host growth was the result of increased antagonistic symbiont behavior in the form of gill tissue consumption. Our results suggest microplastics caused a reduction in epibiont abundance, thus decreasing symbiotic resource availability. This reduction in resources resulted in a shift of context dependency, thus increasing parasitic symbiont behavior. This study demonstrates microplastics have the capability to shift symbiotic context from a mutualism to a parasitism. / Master of Science / Every year, due to improper waste management, approximately 82 million tons of global plastic waste ends up in the environment. Once in the environment, this plastic waste naturally breaks down into tiny particles known as microplastics. Recently, there's been growing concern about how these microplastics affect freshwater habitats. One particular worry is the impact that this contaminant can have on the relationships between different organisms living in freshwater environments. Currently, multiple scientific experiments have studied the effects of microplastics on marine and land-based organismal relationships, however, none have studied the effect of microplastics on freshwater organismal relationships. To explore this, we used the relationship of crayfish and a type of worm called Branchiobdellida, due to their close, prolonged relationship commonly found in nature. These Branchiobdellida worms live on the outside of crayfish and keep the gills of the crayfish clean by consuming any matter that has grown or lodged itself on the gill filaments. As such, the worms rely on the crayfish as a home and means of collecting food. Depending on food availability, this relationship can be mutually beneficial for both the crayfish and worm. Due to the worm's reliance of the crayfish and the mutually beneficial relationship they facilitate, the crayfish-branchiobdellidan relationship is known as a symbiosis. To best understand how microplastics affect the crayfish-branchiobdellidan symbiosis, we conducted experiments where we exposed crayfish with varying numbers of worms to a controlled dosage of microplastics for a prolonged period of time within artificial environments called mesocosms. Each microplastic dosage contained different types of microplastics, that mimicked the type and amount commonly found in nature. We found that crayfish with higher worm densities grew less when exposed to microplastics compared to those not exposed to microplastics. We also noticed that when microplastics were present, the worms exhibited more aggressive behavior, like consuming the gills of the crayfish. Based on assays which measured the number of resources accessible to the symbionts, our findings suggest that microplastics reduce the resource availability to the worms, which then triggers a change in their relationship with the crayfish host. Instead of being helpful, the worms start behaving more like parasites when exposed to microplastic. Ultimately, this study shows that microplastics can change the way different organisms interact, turning a beneficial symbiosis into a harmful one.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/119551 |
| Date | 27 June 2024 |
| Creators | Braswell, Cameron Bryce |
| Contributors | Biological Sciences, Brown, Bryan Lyle, Barrett, John E., 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/ |
Page generated in 0.0136 seconds