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Researchers: brine shrimp counts low through winter but models point to strong cyst production this fall
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Summary
Spring brine shrimp (Artemia) counts dropped in January–March, but researchers reported model-based predictions that, after removing sampling outliers, place expected cyst density for the coming fall in a favorable range. Factors such as salinity, chlorophyll, grazing and freshwater inputs were flagged as uncertainties.
Connor Simon, a biologist with the Great Salt Lake Institute program, presented spring monitoring and a harvest model that projects fall cyst density for brine shrimp.
Simon reviewed surface temperature, salinity, chlorophyll and cyst-density time series and said spring counts (January–February) ranged from about 18.7 to 41.33 nauplii (systs) per liter. Using a two-piece regression model that separates density-independent and density-dependent dynamics, the team generated a predictive fall cyst density. "We are poised for good cyst production this coming fall," Simon said, noting model uncertainty from environmental drivers and sampling variability.
Simon and colleagues described how outlier samples (extreme streaks through the brine layer) influence predictions. When extreme outliers were removed, the predicted fall cyst density shifted from roughly the low-40s cysts per liter to an expected value in the mid-30s (after certain high outliers were excluded). The model runs both with and without flagged outliers; Simon said removing extreme values tightened confidence intervals but did not change the overall positive outlook.
Presenters reviewed life-stage time series: early-year adults largely died off during cold months, juveniles began to appear earlier than in recent years, and peak hatching occurred earlier than historical averages, producing a new maximum for March counts at some sites. Simon cautioned that juvenile counts remain low in absolute terms but indicate progression past a winter bottleneck. He also showed new data on brine-fly larvae (bycatch enumerations from plankton tows) that yielded low winter densities with an uptick in February; the significance of fly larvae in lake ecology is still under study.
Gary Golovksi (University of Notre Dame) and others discussed mechanisms that might explain low chlorophyll despite conditions that earlier years supported blooms: dilution by rising lake volume, recolonization of microbialite biofilms that draw down nutrients, and altered north/south connectivity that changes nutrient flux. Presenters emphasized that predicting recruitment and cyst production depends on a complex mix of salinity, nutrient availability, grazing pressure and hydrology.
Presenters described methods, including vertical plankton tows and refractometer surface-salinity measurements, and noted that March hatching made some spring samples unusable for predictive purposes (the model used January–February data to avoid hatch-driven declines in nauplii). No regulatory decisions were taken; this was a technical status update and modelling briefing.
