Growth and reproduction of gelatinous zooplankton exposed to low dissolved oxygen

The lobate ctenophore Mnemiopsis leidyi and the scyphomedusan jellyfish Chrysaora quinquecirrha are seasonally important consumers in the food web of Western Atlantic and Gulf of Mexico estuaries, including Chesapeake Bay. The abundance and importance of these gelatinous species may be increasing as a result of anthropogenic alteration of these systems, particularly the increasing severity and extent of low dissolved oxygen. Ctenophores and jellyfish are more tolerant of hypoxia than co-occurring finfish, and can sustain high feeding rates in hypoxic waters. We examined the effects of hypoxia exposure on M. leidyi and C. quinquecirrha growth rates and M. leidyi reproduction over 4 d periods in 1 m(3) mesocosms at a range of natural prey densities. Both small (0.2 to 2.0 ml biovolume) and larger (8.0 to 17.6 ml biovolume) ctenophores had significantly reduced growth at oxygen levels of 1.5 and 2.5 mg l(-1) as compared to air-saturated water, especially at high prey densities. Egg production by large ctenophores was also significantly reduced by exposure to low dissolved oxygen concentrations. In contrast, C. quinquecirrha growth rates were unaffected by low dissolved oxygen concentrations tested. These results are counter-intuitive as M leidyi preferentially utilizes moderately hypoxic bottom waters in the field, while C. quinquecirrha avoids such waters. Our findings suggest that hypoxia may differentially affect population growth of these dominant gelatinous species.