Farmington Bay is a hypereutrophic embayment of the Great Salt Lake. Monitoring of brine shrimp (Artemia franciscana Kellogg) populations had indicated that brine shrimp densities in Farmington Bay are only 61% of those in the Great Salt Lake. Lower densities may be due to water quality issues or to predation by an invertebrate predator, the water boatman (Trichocorixa verticalis) that thrives in the lower salinity water of Farmington Bay. To determine the impacts of water boatman predation on brine shrimp populations, we performed two mesocosm experiments in Farmington Bay during Fall 2003. Replicate treatments either included or omitted water boatmen from 60-L tubes. In the 2-day long Experiment 1, water boatman predation had no effect on adult brine shrimp mortality (25% mortality with corixids, 29% without). However there was significantly higher juvenile mortality in predator treatments than in controls (62% vs. 34%). In Experiment 2, adult male and female brine shrimp were added to each tube and mortality was examined after two weeks to allow natural recruitment with and without predators. Experiment 2 also showed corixid predation had no effect on adult brine shrimp densities, but juvenile brine shrimp densities in the predator treatments were only 47% of the controls, indicating that under nearly natural conditions, water boatmen can exert an important control on brine shrimp populations by decreasing juvenile recruitment.
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