UC San Diego

Jellyfish blooms and their effects on ecosystems and humans are sources of increasing concern. In this dissertation, I examine the conditions to which the bloom- forming jellyfish Aurelia sp1 are exposed in San Diego embayments and perform laboratory experiments to explore the tolerances of polyps, ephyrae, and juvenile medusae to environmentally relevant changes in salinity, dissolved oxygen, and dissolved organic matter (DOM). In Mission Bay, Aurelia sp1 polyps were present year-round from 2008 - 2012. Strobilation and ephyrae production occurred in late autumn, continuing through winter. Medusae were only collected in winter and spring of 2008. In San Diego Bay, ephyrae were present each winter and medusae were present each spring. Combining my data with presence/absence records from other sources extending back to 2000, in years with high precipitation, medusae were absent in Mission Bay, but present in San Diego Bay. The timing of precipitation events coincides with the presence of ephyrae, suggesting that low salinities in Mission Bay caused high mortality of ephyrae, leading to recruitment failure and the absence of medusae. When exposed to acute salinity changes, Aurelia sp1 polyps can survive for at least 72 h at salinities from 6 to 52 psu. Ephyrae are more sensitive, surviving from 17 to 40 psu. Juvenile medusae have salinity tolerances similar to ephyrae, but survive longer than ephyrae at the same salinities. Aurelia sp1 polyps survive for at least 28 days when exposed to dissolved oxygen levels as low as 0.8 mg L⁻¹. Ephyrae survived for 10 days at similar oxygen concentrations. Ephyrae exposed to hypoxia have lower C and N content than those exposed to air-saturated conditions, while polyps show no change. Exposure to dissolved organic matter (DOM) had little impact on growth or survivorship of Aurelia sp1 polyps over 3 months. With and without DOM, fed polyps increased in abundance and starved polyps decreased in abundance. Unfed polyps in artificial sea water had lower C and N content than fed polyps in filtered sea water, but DOM made no difference within fed and unfed treatments. Aurelia sp1 population dynamics may be particularly sensitive to survivorship of ephyrae