Microbialite Communities and Food Web Linkages in Great Salt Lake, Utah, USA

Great Salt Lake (GSL) is a large hypersaline lake with simple benthic and pelagic food chains characterized by high production of invertebrate herbivores, brine flies (Ephydra spp.) and brine shrimp (Artemia franciscana) that feed upon phytoplankton and attached algae on benthic microbialites. Over the course of its recorded history, GSL water levels have fluctuated in response to climate patterns and human interventions, which affect abiotic conditions and food web components. However, studies of benthic responses to abiotic conditions and the role of microbialites in the food web are few and a major gap of knowledge. As concerns about the potential impacts of climate change and human development on the GSL food web increase, understanding the effects of changing abiotic factors on the benthic and pelagic components is crucial for managing and protecting productivity.

Three objectives guide this research: 1) Characterize microbialite primary producer and diversity responses to changing abiotic conditions; 2) Determine the effects of physical and biotic factors on food web components and how future climate changes may affect GSL; and 3) Provide an initial assessment of benthic-pelagic linkage and herbivore population responses to changing food availability and abiotic conditions. My review of historical and recent GSL studies showed that changes in temperatures and nitrogen were more impactful than salinity on primary producers and consumers. Microbialite primary producers in the lab grew best at low salinity and intermediate temperature, and diversity increased with temperature and declined with salinity and showed a positive relationship with primary producer abundance. Lab studies showed that both herbivores survived best at 90 ppt salinity and 10°C, but brine fly larvae performed best on diatoms and least on cyanobacteria, while brine shrimp exhibited opposite responses. Field studies revealed a mid-summer benthic-pelagic linkage in which brine shrimp feed on microbialite-associated production and potentially compete with brine fly larvae when their primary food source, phytoplankton, are depleted. This work provides a first comparative assessment of benthic and pelagic responses to abiotic changes and establishes a seasonal linkage that suggests microbialites are an important resource sustaining brine fly and brine shrimp production in GSL.