Viability and hatchability of brine shrimp Artemia franciscana cysts after passing through the digestive system of eared grebes Podiceps nigricollis

Brine shrimp Artemia franciscana provide food for many migrating and staging birds that spend summer and fall on Great Salt Lake, Utah, USA. Artemia produce live young and cysts (hard-walled eggs); these cysts are commercially harvested on Great Salt Lake and support a large industry in Utah. It is unclear the impact that millions of hungry birds have on the Artemia population in the lake. To help assess that, this study evaluated cyst viability (percentage of cysts that contain an embryo) and hatchability (percent of cysts that hatch) from cysts that had passed through the digestive tract of eared grebes Podiceps nigricollis and cysts obtained directly from Great Salt Lake at the same site where each grebe was collected. Hatchability was significantly higher for cysts collected from the water column (19%) than from the stomach (0.3%) or intestines (3%) of eared grebes. Viability also was significantly different for cysts collected from the water column (29%), stomach (0.7%), and intestines (5%). These results indicate that eared grebes nutritionally benefit from eating cysts and that they may be an important food source for grebes in late fall after the adult population of Artemia dies off due to the water becoming too cold. Also, enough cysts survive their passage through the digestive system that grebes can vector hatchable cysts to other waterbodies.