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

Outbreaks of jellyfish are reported worldwide, yet the environmental factor s 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 dramati c annual variations that are correlated with salinity and temperature. We m easured 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 fact or at low salinities (5 to 20 parts per thousand); however, ephyra producti on increased significantly with increasing temperature at high salinities ( 20 to 35 parts per thousand). Conversely, each 5 degrees C: decrease in tem perature delayed strobilation (ephyra production) by about 1 wk. Salinity s ignificantly affected the numbers of ephyrae and polyps produced in all exp eriments. Ephyra and polyp production was lower at both low (<11 parts per thousand) and high salinities (greater than or equal to 25 parts per thousa nd) than at intermediate salinities. Also, more ephyrae, but, not polyps, w ere produced with more available prey. Medusa numbers were 2 orders of magn itude lower in July 1996 when water temperatures, salinities, and zooplankt on densities in Chesapeake Bay all were lower than in July 1995. The effect s of these factors are important in understanding the changes caused by hum an activities in near-shore ecosystems, including effects of global warming , eutrophication, and reduction of commercial species.