Temperature, salinity and food effects on asexual reproduction and abundance of the scyphozoan Chrysaora quinquecirrha

Outbreaks of jellyfish are reported worldwide, yet the environmental factors that control the sizes of jellyfish populations are not well understood. The scyphomedusan Chrysaora quinquecirrha occurs in the mesohaline portion of Chesapeake Bay each summer. Population sizes of the medusae show dramatic annual variations that are correlated with salinity and temperature. We measured the total numbers of ephyrae and polyps produced by benthic polyps of C. quinquecirrha in laboratory experiments lasting 42 d, and found that temperature (15, 20, 25 degrees C) was not a statistically significant factor at low salinities (5 to 20 parts per thousand); however, ephyra production increased significantly with increasing temperature at high salinities (20 to 35 parts per thousand). Conversely, each 5 degrees C: decrease in temperature delayed strobilation (ephyra production) by about 1 wk. Salinity significantly affected the numbers of ephyrae and polyps produced in all experiments. Ephyra and polyp production was lower at both low (<11 parts per thousand) and high salinities (greater than or equal to 25 parts per thousand) than at intermediate salinities. Also, more ephyrae, but, not polyps, were produced with more available prey. Medusa numbers were 2 orders of magnitude lower in July 1996 when water temperatures, salinities, and zooplankton densities in Chesapeake Bay all were lower than in July 1995. The effects of these factors are important in understanding the changes caused by human activities in near-shore ecosystems, including effects of global warming, eutrophication, and reduction of commercial species.