Abstract
Blooms of the scyphozoan jellyfish Aurelia aurita are greatly regulated by the survival rate of planktonic ephyrae. The ecophysiology of ephyrae is poorly studied compared with polyps and medusae. As extremely strong starvation resistance and recovery capability of A. aurita ephyrae may due to its low metabolic rate as well as starvation may reduce the swimming ability of ephyrae which may lead to the higher predation loss, the effects of temperature and starvation on their respiration and pulsation rates were examined. In this study, ephyrae under different starvation conditions were measured by a fluorescence-based DO meter after 72 h incubation. And the pulsation rates were measured at every 10-d interval in 1-liter plastic bottle by a hand-held counter. The results showed that the mean respiration rates of newly released ephyrae were 0.24, 0.24 and 0.19 μl O2 ephyra-1 d-1 at 15°C, 12°C and 9°C, respectively, and the rates tended to decrease with increasing starvation duration. Carbon weight-specific respiration rates did not change significantly with starvation duration. The dry weight-specific respiration rates of newly released A. aurita ephyrae (i.e., 11.7-14.6 μl O2 mg DW-1 d-1) were nearly one order of magnitude lower than the rates for planktonic larvae of other taxa (e.g., molluscs, crustaceans and fish). The maximum pulsation rate taken by A. aurita ephyrae was 49.2 beats min-1, which represents the maximum swimming velocity to be 8.87 cm·min-1. The pulsation rates were not affected by temperature over the range between 9°C and 15°C. However, they were influenced by starvation duration. Starvation-derived decrease in pulsation together with associated body shrinkage may lead to lower encounter rate of prey and lower escaping ability from predators, which may lead to higher predation loss in the field.
Highlights
The moon jellyfish Aurelia aurita s.l. is the most common scyphozoan jellyfish in coastal waters around the world, and mass occurrences of this species have been reported from various regions
The results showed that the mean respiration rates of newly released ephyrae were 0.24, 0.24 and 0.19 μl O2 ephyra−1 d−1 at 15 ̊C, 12 ̊C and 9 ̊C, respectively, and the rates tended to decrease with increasing starvation duration
The effect of starvation on respiration rates and pulsation rates of A. aurita ephyrae was investigated, because we considered their extremely strong starvation resistance and recovery capability may be attributed to their low metabolic rates and their swimming ability is closely associated with feeding and escaping capabilities
Summary
The moon jellyfish Aurelia aurita s.l. is the most common scyphozoan jellyfish in coastal waters around the world, and mass occurrences of this species have been reported from various regions. In the life cycle of A. aurita, planktonic ephyrae play a critical role in population recruitment since the mortality of ephyrae can significantly influence the subsequent population of medusae [9] [10]. Studies on this vulnerable stage have seldom been reported. Our previous study found that A. aurita ephyrae have extremely strong starvation resistance and recovery capability, which are indicated by their extraordinarily long PNR50 (i.e., duration of starvation at which 50% of ephyrae could recover from starvation and grow to the stage) [9]. We consider that such starvation resistance and recovery capability may be attributed to extremely low metabolic rates of starved ephyrae
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