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Jellyfish are important components of aquatic ecosystems and may interfere with human priorities through damage to fisheries, tourism, and power production. Jellyfish populations are renowned for large, unexplained outbreaks (blooms) that may be affected by polyp density and environmental factors, including temperature, salinity, light, and food. In this study, 14 to 15 sites underneath marina floats were monitored by monthly photographs; temperature, salinity, and light intensities were recorded beneath the floats from December through March in 3 yr in order to quantify the amounts and times of strobilation of the moon jellyfish Aurelia labiata in relation to polyp density and environmental factors in Cornet Bay, Washington, USA. Strobilation occurred during February 2004 (Year 1), January and February 2005 (Year 2), and February to April 2006 (Year 3), when temperature, salinity, and light were increasing after the annual minima. Polyps averaged 58% cover and densities of 9.3 cm -2 with little variation among years. Polyp densities were not correlated with the amounts or start times of strobilation. By contrast, the amounts and times of strobilation and all physical factors tested (temperature, salinity/precipitation, light) differed significantly among years. Strobilation was greatest (~63% of polyps) and earliest in Year 2, when pre-strobilation temperature and daily light exposure were high and precipitation was low. The differences in amounts and times of strobilation were greater than predicted from previous laboratory experiments, thus suggesting additive effects of environmental factors. Warm temperatures, nutrient delivery from run-off, and high sunlight enhance plankton production, providing abundant food for the polyps and new jellyfish, and those environmental cues synchronize jellyfish and plankton production.
Purcell et al. (Mon,) studied this question.