Faxonius rusticus impact on the biodiversity of benthic macroinvertebrate assemblages in the Conodoguinet Creek

doi:10.21203/rs.3.rs-4676095/v1

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Faxonius rusticus impact on the biodiversity of benthic macroinvertebrate assemblages in the Conodoguinet Creek

https://doi.org/10.21203/rs.3.rs-4676095/v1

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The Rusty Crawdad (Faxonius rusticus) is a species invasive to the streams of Pennsylvania, chiefly the Conodoguinet Creek. However, little research has been done to investigate Faxonius rusticus’ impact on the biodiversity of the Conodoguinet’s particular ecosystem. The biodiversity of benthic macroinvertebrates is often used to determine the health of lotic ecosystems and as such was tested in order to analyze the mechanisms through which Faxonius rusticus may be altering the creek’s food web. Although the results exhibited a degree of discordance, data collected via this method suggested that biodiversity of the Conodoguinet was generally of good quality despite the presence of Faxonius rusticus. Thus, it was speculated that Faxonius rusticusmay be beneficial to the Conodoguinet Creek ecosystem due to its predation on another invasive species residing in the Conodoguinet: the Asian clam (Corbicula fluminea). Faxonius rusticus may have been able to uphold the biodiversity of this ecosystem’s benthic macroinvertebrate assemblages by precluding the explosive growth of Corbicula fluminea populations and thus allowing native species to compete. As a result, this study suggests that invasive species, such as Faxonius rusticus, may have complex effects on biodiversity varying by ecosystems’ specific food webs.

Rusty Crawdad (Faxonius rusticus)

Conodoguinet Creek

invasive species

biodiversity

benthic macroinvertebrates

Asian clam (Corbicula fluminea)

Increasing at a rate comparable to climate change (Mooney and Cleland 2001), the spread of invasive species across the globe has garnered significant attention for its incredible impact on the balance of ecosystems. Capable of destroying native species’ populations and triggering tremendous trophic cascades—the disruption of an entire food web (Walsh et al. 2016)—invasive species are recognized to affect the critical ecological stability of their entire ecological community. Conversely, in some instances, invasive species can have positive ecological effects in their ability to increase biodiversity through speciation, increasing overall ecosystem tolerance (Mooney and Cleland 2001). The prevalence of invasive species is also economically impactful due to biodiverse communities’ ability to provide large amounts of eco-exergy, a factor that directly influences the profitability of ecosystem services: the monetary value of the services provided by an ecosystem for human benefit (Vihervaara et al. 2019).

Additionally, the integration of invasive species is further perpetuated by secondary anthropogenic influences. For instance, urban stream syndrome, the presence of roads near a lotic (fast-moving freshwater) environment disrupting its biotic niche, and increasing rates of climate change, both alter the state of the ecosystem, reducing the significance of an invasive species’ lag phase-the period in which an invasive species must adapt to its new ecosystem (Babbington et al. 2023, Mooney and Cleland 2001). These lag phases usually prevent invasive species from assimilating into foreign environments. However, anthropogenic impacts create a similar lag phase for native species as they adapt to their own niche’s rapid environmental changes (Mooney and Cleland 2001).

Specifically within stream ecosystems, benthic communities (bottom-dwelling organisms in an aquatic ecosystem) are threatened by the invasive species of crawdad: Faxonius rusticus (F. rusticus: the rusty crawdad). F. rusticus, a highly competitive species which is capable of altering ecosystems, has been documented to out-compete native species across the globe and disturb organisms throughout the entirety of its benthic food web (Laffitte et al. 2023, Twardochleb et al. 2013). Having been spotted in Central Pennsylvania (Shull and Pulket 2015), invasive populations of F. rusticus may significantly affect the benthic macroinvertebrate trophic pyramid. A key to understanding the complex ecosystem circumstances driving the conflicting positive/negative nature of invasive species’ impact, the role of F. rusticus as an invasive species impacting the biodiversity of its benthic macroinvertebrate community has yet to be quantified in all ecosystems. Susceptible to the anthropogenic impacts introduced by urban stream syndrome and climate change (Senus et al. 2004), the Conodoguinet Creek, a lotic ecosystem with a significant presence of invasive F. rusticus (Shull and Pulket 2015), serves as a reference point to determine the exact ecological impact of F. rusticus. This raises the question: To what extent does the presence of Faxonius rusticus impact the biodiversity of benthic macroinvertebrate assemblages in the Conodoguinet Creek?

The prominent economic perspective on the assimilation of invasive species solidifies the importance of biodiversity. Focusing on the prospects of ecosystem services (ES), the monetary value of the services provided by an ecosystem for human benefit, this economic perspective highlights the importance of optimizing environmental thermodynamic efficiency through the concept of eco-exergy: “the complexity of ecosystems in relation to the chemical energy stored in organic matter and the genetic information embodied in the biomass of living organisms” (Vihervaara et al. 2019 p. 27). Achieving high eco-exergy is attributed to increased biodiversity as a higher number of different species can capture more of the available energy in an environment in different ways, increasing energy-use efficiency. As a result, biodiversity supports more profitable ES, a valuation that is known to significantly decrease the prices people pay for goods and services (Vihervaara et al. 2019). However, economists often limit their knowledge of invasive species to that emphasized by the negative ecological perspective. As a result, their studies only quantify invasive species’ negative impact on biodiversity. For instance, a study analyzing the economic drawbacks of the depletion of a species of water flea due to the introduction of an invader finds that the subsequent water clarity damage was sufficient to warrant a $140 million repair fee (Walsh et al. 2016). The significance of ES on the economy demonstrates biodiversity’s crucial role in determining the impact of invasive species.

Traditionally within the field, invasive species are recognized for their damaging environmental effects through a negative ecological perspective. Outlining the myriad of historically documented evolutionary effects caused by invasive species, Mooney and Cleland find two major sources of their negative impacts: the out-competition of native species and the onset of multi-trophic level devastation (Mooney and Cleland 2001). First, invasive species, due to their lack of predators, are highly competitive for food availability with their native counterparts (Mooney and Cleland 2001). For example, F. rusticus has been shown to outcompete native crawdad species. Specifically in its invasion of French benthic ecosystems, F. rusticus was found to be a highly aggressive competitor for food with the native species, aiding in the destruction of native crawdad populations (Laffitte et al. 2023). Additionally, invasive species’ high consumption of food resources can lead to trophic disturbances that extend beyond direct competition. Triggering what is known as a trophic cascade, the introduction of the invasive species Bythotrephes to an aquatic system resulted in the imbalance of the area’s entire food chain, reducing the Daphnia pulicaria biomass by 60% (Walsh et al. 2016). The negative impact of invasive species on ecosystem function is moreover corroborated by a study investigating various benthic macroinvertebrate assemblages in Japan’s Dianichi Basin. In this study, sample areas with decreased biodiversity, species richness, and sensitive species taxa (species of similar evolutionary origin) were found to have degraded habitat conditions, a factor directly linked to extinction (Cao et al. 2018). The consequences of invasive species can be additionally speculated to have a direct impact on the Conodoguinet Creek. Invasive crawdads (such as F. rusticus) are found to have “significantly and negatively affected biomass and abundances of macrophytes, invertebrates (all benthic invertebrates and snails specifically), fish, and amphibians[...]across multiple levels of freshwater food webs” (Twardochleb et al. 2013 p. 1376). Overall, invasive species have been recognized within literature to negatively impact native competitors and the stability and biodiversity of the ecosystem as a whole due to their ability to induce trophic cascades.

Despite the prevalence of this negative perspective, it is also important to note the positive ecological impacts found within literature. Instead of always facing extinction, native species are conversely able to live cohesively with invasive species via resource partitioning, the division of resources between competing species, or hybridization, the interbreeding of species into a new species (Mooney and Cleland 2001). As a result, both may lead to an increase in biodiversity as resource partitioning ensures the evolution of native species to adapt to more selective pressures and hybridization involves an increase in genetic variation due to native-invasive breeding, thus invoking speciation (Mooney and Cleland 2001). This explanation works to rationalize the results demonstrated by a study examining benthic macroinvertebrate assemblages upstream and downstream from a dam. Although the anthropogenic influence of the dam was specifically measured to aid in the establishment of the invasive species Corbicula fluminea and Melanoides tuberculata, biodiversity was found to increase directly downstream (Linares et al. 2018). Thus, in some ecosystems, invasive species can benefit benthic macroinvertebrate communities in a way that increases biodiversity. Additionally, invasive species may increase the stability of an ecosystem due to their generally higher environmental tolerance, a characteristic that is particularly critical due to the influences of global warming (Mooney and Cleland 2001, Bonebrake and Mastrandrea 2010). In this way, invasive species are able to likewise be of value in conservatism, strengthening the validity of the positive ecological perspective. Finally, a study quantifying the trophic effects of the invasive Green sunfish (Lepomis cyanellus) in an urban stream reveals the potential positive trophic effects of invasive species. Finding that it can preclude the over-dominance of the benthic species Chironomidae, the Green sunfish’s consumption of this biodiversity-limiting species was able to overcome the eutrophic effects aiding Chironomidae’s growth (Babbington et al. 2023). Instead of always negatively impacting the benthic community surrounding them, invasive species have the potential to create beneficial tropic effects in specific niches.

The conflicting ecological perspectives demonstrate the complexity of the various circumstances that shape invaders’ ultimate consequence on an environment’s ecology. Invasive species’ effect on biodiversity, particularly through trophic cascades, has examples within relevant literature that can be either detrimental or beneficial, despite the zeitgeist around their assimilation. Thus, the dynamic argument surrounding the impact of invasive species changes, based on the specific niche in question. Environmental researchers Russell et al. specifically address this point of contention in their study by consequentially emphasizing the recognition of positive and negative effects in their analysis and conclusion (Russell et al. 2014). To reduce my study’s bias towards either the positive or negative perspectives, it is critical that I investigate both possibilities. In this way, I may determine how disparities in my location of inquiry, the Conodoguinet Creek, contribute to my specific results.

To understand the potential impact of F. rusticus as an invasive species to the Conodoguinet Creek’s specific niche, it is critical to understand the current state of its macroinvertebrate assemblages. While no studies specifically evaluate the health of the Conodoguinet Creek, a study analyzing the biodiversity of Middle Penns Creek, a similarly situated stream in Central Pennsylvania’s watershed, reveals the general properties of benthic macroinvertebrate assemblages that are comparable to my area of interest. In this study, the majority of applicable streams assessed were found to exhibit high biodiversity, where the data revealed an average Shannon diversity index score of 89.0 and an average benthic macroinvertebrate index of biological integrity score of 80.5, indicating the majority to be high quality or exceptional value waters (Panas et al. 2014) However, the health of the system indicated by the study was also noted to be prospectively degraded by anthropogenic impacts—where instances of poor biodiversity index quantifications were explained by the presence of factors such as road crossings and agricultural areas due to their direct harm on many of the residing taxa due to their sensitivity (Panas et al. 2014). In this instance, the Conodoguinet Creek becomes of specific interest as only 32.6% of its surrounding land is forested, leaving 3.7% developed and 62.2% agricultural (Senus et al. 2004). Due to the aforementioned connection between anthropogenic impact and invasive species, it can be speculated that the Conodoguinet harbors a large population of invasive species. In recent years, the onset of a F. rusticus invasion in Central Pennsylvania has been documented by the Pennsylvania Department of Environmental Protection and featured in news outlets such as The Shippensburg News-Chronicle, and PennLive/The Patriot-News (Shull and Pulket 2015, Potts 2022, Gilliland 2012). As the development of F. rusticus as a prominent invasive species in Central PA’s watershed continues, the anthropogenic effects impacting the Conodoguinet Creek may therefore perpetuate the invasive species’ assimilation into the Conodoguinet’s niche.

The presence of invasive species’ predicted impact on an individual ecosystem’s biodiversity is a debated topic that is seemingly unclear until specifically isolated and quantified. Regardless of ultimate positive or negative effect, relevant literature suggests aquatic invasive species are of significant impact on benthic macroinvertebrate assemblages due to the potential of trophic cascades. However, F. rusticus’ direct impact on benthic species has yet to be quantified in terms of biodiversity, a factor particularly critical to ES. In an attempt to clarify this gap in research, this study aims to address the question: to what extent does the presence of Faxonius rusticus impact the biodiversity of benthic macroinvertebrate assemblages in the Conodoguinet Creek? Quantifying the biodiversity of the benthic macroinvertebrate population as a whole will first reveal F. rusticus’ ecological impact, helping clarify in what environments invasive species might be either beneficial or detrimental. Additionally, in assessing biodiversity of benthic macroinvertebrate assemblages in direct correlation with F. rusticus, this study can address the stability and ecosystem service potential of the Conodoguinet Creek environment. These specific relationships were neglected in previous research due to their broader or redirected focuses often centered around an anthropogenic effect, invasive-native species competition instead of trophic effect, biomass instead of biodiversity, or a significantly different invasive species. Due to the variability of ecosystems in their response to invasive species due to their unique food webs, it is critical that the Conodoguinet Creek be individually assessed.

Macroinvertebrate samples were collected and transformed into quantifications of biodiversity in order to measure the impact of F. rusticus populations on benthic macroinvertebrate assemblages in the Conodoguinet. The kick sampling method was used to collect benthic macroinvertebrate samples, a technique commonly used within the field-such as in Panas et al. and McGovern et al.’s work-that employs the researcher(s) to disrupt the benthic community in a wadeable stream (such as the Conodoguinet) using their feet to draw out a representative sample of all benthic macroinvertebrates present. Due to the location of this study, I specifically followed the guidelines provided by the PA DEP on the kick sampling method. Organisms were identified using a dichotomous key provided from Stroud Water Research Center, similarly to the procedure in Panas et al.’s study. Three trials at all three sampling sites were performed to ensure data accuracy and replicability. The results obtained from this study follow similar integrity to Panas et al.’s as both were performed in a similar allotment of time, followed PA DEP guidelines, and were performed in the state of Pennsylvania. Although a multi-seasonal study is generally recommended for this method design, data produced by this study can still be considered valid as Panas et al.’s study was able to collect statistically relevant results (in the form of biodiversity quantifications) despite only being performed for roughly one month during the relatively cold season of October-November.

Benthic Macroinvertebrate Sampling

At each sampling site, three trials were performed using the kick sampling method outlined by the PA DEP. Trials were originally intended to be performed sequentially with 10 minute intervals in between for the researcher and volunteers to recuperate. However, some trials from the same sampling site were performed on different days due to time limitations created by flood stage conditions in the Conodoguinet during the window of this study. Volunteers were used in this study to ensure as many benthic macroinvertebrates were collected to most accurately represent the macroinvertebrate assemblage present. No more than three volunteers assisted in data collection at one time. All volunteers signed a liability form in order to obtain a consent to participate declaration and were provided with a paddling jacket and waders. Copies of the liability forms signed by the volunteers are not included in order to maintain volunteer identity confidentiality. At no point did the researcher or any volunteer enter the water deeper than the height of their waders. In order to ensure ethicality, the method of this study was approved by the IRB at Cumberland Valley High School.

Trials were performed with upstream progression to ensure the testing area was undisturbed by previous trials while still representing fundamentally the same macroinvertebrate assemblage (Letovsky et al. 2023). Boundaries of each trial were marked using two wooden stakes parallel to the streambed around 1.5 meters apart. Trials lasted 16 minutes. Benthic macroinvertebrates were collected using a D-frame net and two finer nets to collect the broadest range of organisms possible. Benthic matter captured in nets was sifted through to ensure burrowing species were accounted for. Captured macroinvertebrates were transferred to a plastic container to be photographed for later identification. It should be noted that most studies, such as Panas et al., preserve all specimens in an ethanol or formaldehyde solution for later identification in a laboratory setting. As the researcher is not trained to work with hazardous chemicals, this study instead used photography to identify organisms collected with the most certainty possible. All equipment was sanitized between sample sites to prevent cross-contamination.

Sampling Sites

This study examined three sample sites in the Conodoguinet: Vincent DeFilippo Nature Preserve (site 1), Good Hope Access (site 2), and Oyster Mill Park (site 3). All three of the sites are public property and therefore adhere to the permissions granted to me through ownership of a Pennsylvania Fishing & Boating License. Three sample sites were chosen to ensure data is representative of the Conodoguinet Creek as a whole. Each sample site was originally intended to be assessed during the duration of 12:00 p.m. to 2:00 p.m. Data from each sampling site was originally intended to be gathered in the same day, however, testing dates were often rescheduled due to unsafe water conditions and the inability to enter the creek due to unexpected flooding. Unfortunately, flood-stage conditions and hazardous weather persisted over the greater majority of this study’s testing window. As a result, the researcher took the initiative to alter the original design of the study, changing testing dates to complete trials non-consecutively (on different dates) for a sample site, and straying from the original time of day window to accrue data from the original number of trials. All data collected was labeled with the time windows and the date of collection to maintain replicability.

Analysis

Organism population data collected during the kick sampling method was then transformed into quantifications of biodiversity through the application of the following biodiversity indices:

Total Taxa Richness
EPT Taxa Richness
Simpson’s Diversity Index
Pollution Tolerance Index (PTI-developed from Hilsenhoff Biotic Index)
Shannon Diversity Index (aka. Shannon-Weiner Diversity Index)
Percent Sensitive Individuals
Macroinvertebrate Biotic Index (MBI)

All online calculators used are listed in Appendix B. Multiple biodiversity indices were used to mitigate the impact of individual indices’ biases. All biodiversity indices used are those recommended by the PA DEP for benthic macroinvertebrate investigations with the exception that Shannon Diversity Index (which was of greater relevance to my study) was used to replace Beck’s index. Beck’s index is primarily used to assess the general health of a stream based on benthic community biodiversity. However, Shannon’s diversity index specifically aims to quantify an ecosystem’s biodiversity. In this way, the data collected in this study can directly address the question “To what extent does the presence of Faxonius rusticus impact the biodiversity of benthic macroinvertebrate assemblages in the Conodoguinet Creek?” by directly observing how the presence of a F. rusticus population impacts the biodiversity quantifications calculated by the structure of the benthic macroinvertebrate assemblages found in the Conodoguinet Creek.

Species Collected

In this study 16 species were collected with an overall average total taxa richness (number of different taxa in a sample) of 8.11 (Fig. 2). Throughout all three sample sites, the F. rusticus population was relatively constant with an average population size of .7778 (site 1: 1, site 2: .6667, site 3: .6667) per trial and an average of 2.33 per sample site (Fig. 2). Although these population sizes seem low, it must be taken into consideration that the majority of the population sizes found for other species were not significantly greater (Fig. 2). Additionally F. rusticus is a substantially large, and aggressive macroinvertebrate (Laffitte et al. 2023), indicating it requires more space in which to live and is thus less population dense than smaller species of benthic macroinvertebrates. With this reasoning, it is highly likely that F. rusticus’ population in this study was significant.

Biodiversity Quantifications

The tables above were generated using average quantifications for each biodiversity index calculated (excluding percent sensitive individuals). Descriptive values (ie. “fair”) were determined using standard charts for decoding specific biodiversity indices provided by the online calculators used (index: MBI, PTI, Total Taxa Richness, EPT Taxa Richness) or by established interpretive charts used in literature such as in Guajardo 2015 (index: Simpson’s Diversity Index) and Reflinaldon & Hamid 2023 (index: Shannon Diversity Index). All qualitative biodiversity index interpretation charts listed in Appendix B and raw data in Appendix C; mean values were used for all calculations as any deviance in data from trial to trial in a sample site can be reasonably discerned to be caused by environmental third variables. Outliers are discussed in the section. For example, at sample site 1, where some biodiversity quantifications indicated “good” (index: MBI, PTI) and “fair” (index: Shannon Diversity Index, Total Taxa Richness) biodiversity, others reported “poor” (index: EPT Taxa Richness, Simpson’s Diversity Index).

The benthic macroinvertebrate biodiversity was of varying quality in terms of pre-established quantitative interpretations of biodiversity determined for specific indices. The discrepancies between the indications of different biodiversity indices may be due to the sample size of this study. As found in a study by Routledge, Shannon’s Diversity Index and Simpson’s Diversity index are both negatively impacted by a small population size due to their reliance on the multiplication of species’ population numbers (Routledge 1980). The mean sample size of macroinvertebrates in this study was 98.33 per trial. These values are unfortunately much smaller than similar studies within the field such as in Panas et al. where the average number of individuals per site was 179.64. As such, the nature of these indices may indicate why the scores from Shannon’s Diversity Index and Simpson’s Diversity Index in this study represented “stable enough” and “low degree of biodiversity”, despite the fact that other biodiversity indices scored biodiversity in these areas as “good” or fair” with the exception of EPT Taxa Richness. Despite the flaw of these two indices’ application to this study, it is still important to discuss what other factors may have influenced their deflated scores as a reflection of the data generated by this study.

Despite the index's occasional disagreeance in overall biodiversity descriptions, the trend in index values between sample sites was quite consistent. For example, site 1, although exhibiting similar biodiversity values to the other two sample sites, reported slightly better biodiversity in all categories (with the exception of sample site 3’s better score for Simpson’s Diversity Index).

Shannon Diversity Index & Simpson’s Diversity Index

First, the Shannon Diversity index is a biodiversity index primarily biased towards favoring samples’ evenness: The ratio of species’ population size (Strong 2016). Thus, a biodiversity quantification produced by the Shannon Diversity Index that indicates generally good biodiversity would include a sample that has both many different species as well as a significant number of each species. Although poor Shannon Diversity Index quantifications could have been simply reflective of poor biodiversity, it is more likely that low values may be more greatly attributed to the large Talitridae population. As seen in Fig. 2, significantly higher populations of Talitridae were found over any other species in every trial, thus negatively impacting Shannon Diversity Index’s accuracy. Similarly, the Simpson Diversity index is known as a dominance index which is greatly determined by the most dominant population(s) in a sample (Kitikidou et al. 2024): in this case, Talitridae. Thus, the Simpson Diversity index is most likely reflective of the same issues as the Shannon Diversity Index. This idea is further supported by the fact that sample site 3, despite being indicated to have the lowest biodiversity according to every other biodiversity index quantification, has the highest biodiversity according to Simpson’s Diversity Index and Shannon’s Diversity Index. This may be because sample site 3 has significantly large populations of species other than Talitridae (Fig. 2), increasing evenness.

The remaining biodiversity indices calculated, with the exception of total taxa richness, are all indices specifically tailored to report the biodiversity of benthic macroinvertebrate samples. Due to the unreliability of the quantifications provided by the Shannon Diversity Index and Simpson’s Diversity Index, a continuation of the analysis of results will henceforth rely on the remaining 5 biodiversity indices quantified.

Macroinvertebrate Biotic Index & Pollution Tolerance Index

MBI and PTI quantifications almost always indicated the biodiversity of all 3 sample sites to be of “good” quality. The MBI reported “good” biodiversity for all three sample sites, while the Pollution Tolerance Index (PTI) reported “good” biodiversity for sample sites 1 and 2 and “fair” biodiversity for sample site 3 (Fig. 4). These two indices Biotic Index are both biodiversity indices specified to measure macroinvertebrate biodiversity and, as such, consider the sensitivity of each species. As Talitridae are classified as “somewhat sensitive” (Stroud water Research Center), these indices are able to control for their large population sizes in a manner that Shannon Diversity Index and Simpson’s Diversity Index were not. The MBI is a holistic index (Monaghan 2016), and, as a result, the “good” biodiversity rating determined from this index represents a more generalized biodiversity indicator that is less biased by specific factors (ie. evenness) than other biodiversity indices in a macroinvertebrate sample. Furthermore, the PTI is able to balance uneven species populations as it focuses very specifically on the sensitivity of populations and was developed to indicate water quality over biodiversity, although it can reveal aspects of both (Chang et al. 2013). This bi-purpose bias of the PTI may be the reason why sample site 3 dipped down to “fair” biodiversity despite being reported “good” for the MBI. This small difference could have also easily been caused by small population sizes decreasing the accuracy of data in addition to the fact that sample site 3 reported the lowest biodiversity (Fig. 3). Regardless, the general agreement of these two more well-specified indices to macroinvertebrate samples reinforces that it is more likely that the Shannon Diversity Index and Simpson’s Diversity index represented flawed quantifications in the context of this study.

EPT Taxa Richness

EPT Taxa Richness is a quantification that solely counts the number of Ephemeroptera, Plecoptera, and Trichoptera taxons within a sample. Although also an index that focuses on quantifying benthic macroinvertebrate samples, EPT Taxa Richness quantifcations for this study reflected low values of biodiversity (Figs. 3 & 4). Although these poor biodiversity indications may be from samples having low populations of these three critical species, indicating that F. rusticus’s presence specifically degrades the densities of these species, it is more likely that these indications are due to a limitation of the research method and the researcher’s experience. First, as found by Letovsky et al., the kick sampling method, despite ultimately determined to be a good method to sample benthic macroinvertebrates overall, does have the inherent limitation of being a poor collection method of caddisflies. Additionally, it should be noted that the researcher is not a professional in this field and may have failed to recognize organisms from these taxons during a trial. Not only is it very easy for macroinvertebrates to hide within the substrate, but caddisflies in particular are able to disguise themselves in a cocoon that has a stick-like appearance. Thus, it is possible that, instead of these EPT taxon being decreased by F. rusticus, the study simply failed to report all EPT organisms collected during trials. This conclusion is further supported by the fact that the general percentage of sensitive individuals was quite high (site 1: 53.61%, site 2: 52.77%, site 3: 51.99%) according to the sensitivities listed by Stroud Water Research Center’s dichotomous key, meaning water quality is likely not the issue. Overall, it is unable to be determined whether the low EPT Taxa Richness scores were lowered by F. rusticus or the study design, and is therefore difficult to draw conclusions from this particular biodiversity index quantification.

Corbicula fluminea

The results of this study most strongly support that biodiversity in the Conodoguinet Creek, as indicated by the PTI and MBI, was generally of good quality despite the presence of F. rusticus. One speculation explaining the results of this study is F. rusticus’s impact on Corbicula fluminea (C. fluminea): an invasive species found at each sample site (Fig. 2). C. fluminea is known to be a prominent predator of phytoplankton and capable of causing multi-trophic level trickle-down effects on the benthic community surrounding it (Cooper et al. 2005). In decreasing the amount of available phytoplankton, a benthic community’s main primary producer, C. fluminea is able to outcompete other benthic macroinvertebrates. This can be seen within the data of this study as, although site 3 had the highest biodiversity in terms of the Simpson’s and Shannon’s Diversity Index, it overall had the lowest biodiversity when considering all other indices calculated (Fig. 4). This is particularly prevalent as sample site 3 had the highest population of C. fluminea (Fig. 2). However, similar to how the invasive green sunfish is able to preclude harmful Chironomidae (Babbington et al. 2023), F. rusticus may be reducing the C. fluminea population. F. rusticus is known to be an aggressive predator that preys on clams (Laffitte et al. 2023, Twardochleb et al. 2013), making it possible for F. rusticus to indirectly increase biodiversity in the Conodoguinet by eliminating a major source of food competition for other benthic macroinvertebrates.

Limitations

It is important to recognize the limitations of this study and how they may affect the data presented. First, there is a major limitation associated with all naturalistic experimental designs due to third variables. Although water temperature, water depth, surrounding descriptions (urban-in close proximity to a bridge and roads), and the number of volunteers participating were all collected as data in this study and were all proved to be relatively constant (see Appendix C), there are countless other third variables outside of F. rusticus and its surrounding food web that could have impacted the biodiversity quantifications of this study.

Furthermore, as previously discussed, the small sample size of this study impacts some biodiversity index quantifications and limits the accuracy of the data in this study. This limitation was unfortunately enhanced by severe weather and the limited amount of time data was able to be collected due to the nature of the AP Research project. Similar issues in the future may be able to be ameliorated by increasing the time allotted for each trial. Despite the index's occasional disagreeance in overall biodiversity descriptions, however, the trend in index values between sample sites was quite consistent. For example, site 1, despite having similar biodiversity values to the other two sample sites, reported slightly better biodiversity in all categories (with the exception of sample site 3’s better score for Simpson’s Diversity Index).

Finally, the expertise of the researcher must also be considered. The researcher is not a professional within the field and, although has experience with the techniques outlined in this paper, the researcher likely lacks knowledge of exact locations of specific species and may also make mistakes within the identification of macroinvertebrates. This issue is worsened by the researcher’s inability to access preservation chemicals to analyze species collected in a laboratory but was instead reliant on photographing organisms collected.

Biodiversity plays a key role in an ecosystem’s thermodynamic efficiency and the economic success of its ES (Vihervaara et al. 2019). Despite the negative impacts of invasive species in some ecosystems, invasive species can be the solution an environmental community needs to maintain biodiversity in others. As suggested by the results of this study and in works such as Babbington et al., invasive species may benefit the biodiversity of an ecosystem via precluding the growth of a more harmful, alternative invasive species. In this case, the Conodoguinet Creek may have been indicated to have biodiversity due to the ability of its F. rusticus populations to predate on the harmful C. fluminea. As a result, it may be beneficial for future studies to explore the question: to what extent does F. rusticus decrease C. fluminea populations? Answering this question would be able to confirm whether or not F. rusticus was able to preclude the overbearance of C. fluminea invasions on benthic macroinvertebrate biodiversity in the Conodoguinet Creek.

Furthermore, it can be speculated from the results of this study that F. rusticus does not always harm the populations of many important, biodiverse species other than its potential impact on EPT taxa species. Since data on F. rusticus and EPT taxa species in this study was inconclusive due to the limitations of the kick sampling method and the researcher’s experience, it may be beneficial for future research to specifically investigate this relationship using alternative sampling methods that can be specified to these species. Such research would confirm whether or not F. rusticus has a negative impact on these critical species and should not be trusted as a long-term solution to maintaining biodiversity in the Conodoguinet Creek.

Finally, this study provides insight into which ecosystems may benefit from an invasive population of F. rusticus. In recognizing the other species in an ecosystem in which F. rusticus has invaded, it may be possible to predict its potential net benefit which would impact any F. rusticus removal protocol. If the relationship between C. fluminea and F. rusticus shown in this study is confirmed through further research, it may be possible to predict a beneficial impact of F. rusticus in other streams in which C. fluminea and F. rusticus similarly coexist. Such indicators, if confirmed through research in many different ecosystems, could lead to easy and quick identifications of the benefit/detriment ratio of invasive species in a variety of ecosystems. Such a system would begin to open the door into how invasive species can strategically be used to support biodiversity which continues to fade across the globe.

ACKNOWLEDGEMENTS

I acknowledge the role of David Emerick as the AP Research proctor for this study which was originally performed under the AP Research curriculum. I also acknowledge Jenny Pyers who advised me throughout my process and lent me much of the equipment used.

FUNDING

No funding was received towards the creation of this work.

ABOUT THE AUTHOR

Author: Madeleine J. Carmichael

Affiliation: Cumberland Valley High School

Location: Mechanicsburg, PA, 17050, United States of America

E-mail: [email protected]

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Pennsylvania Department of Environmental Protection
See appendix entry A-1 and A-2 for guidelines by Shull 2018 and Chalfant 2012.
Dichotomous key provided by Stroud Water Research Center, see appendix entry A-3
See appendix entry D-1for a blank copy of the volunteer liability form.
Weather commonly consisted of snowy/rainy weather that increased researcher/volunteer risk of hypothermia as well as raised water levels to extremely flooded, unsafe conditions.
Referred to in this study as the more specific taxa Heptageniidae
Referred to in this study as the more specific taxa Hydropsychidae

No competing interests reported.

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Faxonius rusticus impact on the biodiversity of benthic macroinvertebrate assemblages in the Conodoguinet Creek

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Abstract

Figures

INTRODUCTION

LITERATURE REVIEW

METHODS

Benthic Macroinvertebrate Sampling

Sampling Sites

Analysis

RESULTS & DISCUSSION

Species Collected

Biodiversity Quantifications

Shannon Diversity Index & Simpson’s Diversity Index

Macroinvertebrate Biotic Index & Pollution Tolerance Index

EPT Taxa Richness

Corbicula fluminea

Limitations

CONCLUSION

Declarations

References

Footnotes

Additional Declarations

Supplementary Files

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