Over the past several decades, anthropogenic pressures such as urban development and climate change decreased the amount of hypersaline lake habitat around the world. However, extensive management efforts throughout recent years transformed Great Salt Lake into an example of how proper management can help retain critical habitat while also providing economic returns. Located in northern Utah, Great Salt Lake sits in one of the deepest portions of the Great Basin. This terminal lake receives input from a 21,500-square-mile watershed. Under average conditions, Great Salt Lake is 75 miles long and 25 miles wide and covers 1,700 square miles. Recent drought conditions and increased upstream diversions throughout the region have reduced the surface area of Great Salt Lake to under 1,000 square miles. Over time, Great Salt Lake has been partitioned into four ecologically distinct bays by the construction of human-made causeways. The North Arm, known as Gunnison Bay, has the highest salinity, ranging from 26-28%. The South Arm, known as Gilbert Bay, ranges in salinity from 10-17%. Due to the lake's extreme salinities, its permanent residents are restricted to a select few halophilic microorganisms, including chlorophytes, brine shrimp, and brine flies. Although the diversity of organisms found within Great Salt Lake is limited, the lake supports a variety of migratory birds which rely on the brine flies and brine shrimp. Annual waterbird surveys on Great Salt Lake revealed that over 10 million individuals from 338 species utilize the wetlands and uplands associated with the lake each year. Of the birds found throughout Great Salt Lake, over 5 million eared grebes and 600,000 Wilson's phalaropes visit each year, representing up to 90% of the North American and 33% of the global population for each species, respectively (Great Salt Lake Ecosystem Program, 2024). To prepare for the next portion of their migration, waterfowl resting at Great Salt Lake require abundant food resources, relying primarily on brine flies and shrimp. Whereas brine shrimp were previously believed to be the primary food source for waterfowl at Great Salt Lake, recent studies revealed that brine flies likely occupy a large portion of bird diets. Vest et al. (2011) observed that 68% of the diet of Common Goldeneye wintering at the lake were comprised of brine fly larvae, while the locations of phalaropes throughout the lake were positively correlated with elevated abundances of brine fly adults and larvae (Frank & Conover, 2019). Although we are only just beginning to understand the dietary importance of brine flies for waterfowl, that these flies may comprise the majority of waterfowl diets and are associated with potentially at-risk species such as the Red-necked phalarope emphasize the need to better understand brine fly population dynamics, ensuring adequate food during future migratory seasons. The process of developing a monitoring protocol for brine flies is complicated by their life history strategies. Brine flies spend most of their lifespan as either larvae or pupae in the benthos of Great Salt Lake, often attached to microbialite structures at shallower depths. These reef-like structures grow extremely slowly, forming as phototrophs deposit calcium carbonate compounds over the course of thousands of years (Lindsey et al., 2020). Therefore, it is critical to develop a non-invasive method of counting fly larvae that does not rely on harvesting or disturbing the microbialites. However, accessing areas where larvae are present is complicated by the lake's extreme conditions; elevated turbidity during certain periods of the year, cold temperatures, and elevated salinity impede traditional visual survey techniques. Thus, the aim of this project is to improve current monitoring strategies for brine flies, enabling us to assess the status of fly populations throughout the lake while simultaneously mapping out their distribution. This information would then be readily available for determining resource availability for higher trophic levels, ensuring Great Salt Lake remains a viable winter staging ground for migratory birds moving forward.

1) Map the distribution of Brine Fly larvae/pupae across the South Arm of Great Salt Lake. 2) Develop and implement a visual-based survey protocol to monitor brine fly populations in the benthic zone of Great Salt Lake. 3) Continue monitoring brine fly populations for the foreseeable future to ensure adequate food for Great Salt Lake migratory birds. 4) Develop a map of the substrate throughout the South Arm of the Great Salt Lake to better understand the distribution of both microbialites and brine fly habitat.

During water years 2021 and 2022, lower amounts of precipitation, combined with diversions upstream of Great Salt Lake, caused the lake's water level to drop rapidly. The sudden decrease in water elevation resulted in several of the microbialite fields around the lake becoming exposed, and the subsequent death of the associating phototrophic communities. This process of microbialite death caused the loss of critical habitat for brine flies, whose larvae rely on the microbialites as both a substrate and food resource. Current survey methods revealed that the brine fly population likely declined during this time, although due to the lack of resources and the difficulties associated with monitoring brine flies, detailed population responses of brine flies to periods of extreme drought have not been documented. Although as the lake's water elevation increased the flies appeared to recover, it is critical we improve our monitoring strategy for these organisms to better understand how their abundances change in response to extreme conditions.

The Division of Wildlife Resources' Great Salt Lake Ecosystem Program (GSLEP) is tasked with monitoring and conserving the lake's ecosystem, within which brine flies play an important role. This project aims to improve our understanding of the distribution and abundance of brine flies across Great Salt Lake, providing us with a more holistic view of how the ecosystem functions and ensuring adequate food for other inhabitants of the lake. This project will also provide us with a protocol that can then be implemented to monitor future changes in brine fly populations under fluctuating lake conditions.

Not applicable

Brine fly larvae are detritivores that play a key role in cycling nutrients back into the lake's ecosystem, many of which stem from dead brine shrimp and potentially other allochthonous inputs from freshwater inflows around the lake. Without the fly larvae, fewer nutrients may be available to phototrophs in the lake, and we may observe a shift in algal communities towards undesirable, potentially toxic algal species.

Not applicable.

Monitoring Brine Fly populations is complicated due to the difficulties associated with sampling the benthos of Great Salt Lake. Most larvae are located either attached or near microbialite structures throughout the lake, many of which are in areas too shallow to permit boat travel and are therefore only accessible by wading. Surveys on foot entail walking into the microbialite fields from the shore and using waterproof portable cameras (i.e., GoPro) to image microbialite structures. However, during winter periods it is not logistically feasible to access the microbialite fields due to the dangers associated with water temperatures and the elevated turbidity, which make photographing the larvae extremely difficult. Additionally, underwater cameras lack the necessary tools to calculate surface area when photographing a microbialite, making it difficult to standardize larvae counts by area surveyed. Finally, to obtain a holistic representation of the brine fly population across the South Arm of Great Salt Lake, it is necessary to visit microbialite fields across the entirety of the lake, which is near impossible to accomplish without motorized transportation. To circumvent the issues associated with sampling larvae by foot and the lack of boat accessibility, we propose using a remotely operated vehicle (ROV) during sampling efforts. Whereas boats require several feet of water to operate, the ROV can venture into much shallower waters, weaving through microbialite fields to arrive at a targeted destination. To reach sites where water levels prevent boat traffic, we will anchor outside of the microbialite field then launch the ROV, controlling the vessel using live video streamed from the ROV to a handheld controller. The ROV that is being requested for this project is outfitted with up to an 8K video camera and several thrustors that allow for precise positioning and replicable photography of brine fly larvae while causing minimal disturbance to the organisms or microbialites. Once launched, the underwater vessel tracks its path and is able to maintain stability despite waves or current using the onboard thrusters, ensuring the photographs are clear and easily analyzed back at the lab. Furthermore, the ROV is outfitted with calibrated lasers that allow users to calculate the area photographed and use this to determine abundance of larvae per unit area. In addition to photographs, the ROV can collect water quality information and bulk water samples, which can then potentially be used to assess which abiotic parameters drive the distribution of brine flies across the lake. Once photographs are collected, they will be brought back to the lab and analyzed using ImageJ software, where we will count the number of individuals in the field of view and determine the area surveyed. Densities calculated from the sample sites will then be extrapolated using the total area of Great Salt Lake containing microbialites to determine the overall abundance of brine flies on the lake. Initial sampling efforts with the ROV will focus on mapping where the brine flies are located throughout Great Salt Lake to determine potential sampling sites. The final number of sampling sites that will be visited during subsequent surveys will be based on the heterogeneity of the microbialite fields across the lake and the variability in brine fly abundances among sites, ensuring the surveys result in accurate representations of the overall population. Due to logistical constraints and to prevent interference with the brine shrimp monitoring program, initial sampling efforts for brine flies will be restricted to once per month for the first year. Depending on the results of the initial year of sampling, both the frequency of survey efforts and the number of sites visited may be altered to better assess annual changes in fly abundance. Similar to the brine shrimp program, the density of brine flies will eventually be communicated with the public through the Great Salt Lake Ecosystem Program webpage, which will display the sampling period and population size. Additionally, a summary of the data and final report will be submitted to the Utah WRI detailing the findings and recommendations for future brine fly sampling efforts.

Please see above under methods.

Not applicable.

Brine Fly monitoring will continue indefinitely following the project, although the sampling strategy and protocol may be modified based on the project's findings.

The purpose of this project is to develop a survey protocol that promotes proper management of brine flies in the Great Salt Lake ecosystem, where the flies occupy a critical role as ecosystem engineers and prey for other members of the food web. This project will improve our understanding of where the flies are located and how the population changes throughout the year, which will ultimately allow us to target and direct conservation efforts towards regions of the lake where brine fly habitat may be at risk. Overall, this project aims to protect brine flies as both members of the Great Salt Lake ecosystem and as a natural resource for other organisms found throughout the lake.