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MEPS prepress abstract   -  DOI:

Rising seawater temperatures affect the fitness of Rhopilema nomadica polyps and podocysts and the expansion of this medusa into the western Mediterranean

Hila Dror, Dror Angel*

*Corresponding author:

ABSTRACT: Since first reported in the eastern Mediterranean in the 1970’s, the swarm-forming scyphomedusa, Rhopilema nomadica, has been continuously expanding westward. We examined the effect of temperature on the benthic stages (polyps, podocysts, and strobilae) to assess whether they are able to survive and reproduce in the western Mediterranean temperature regime (12.2–26.2°C). In the first experiment, polyps and podocysts were maintained at 4 constant temperatures (12, 18, 24, and 30°C; 55 d), and in the second experiment, temperatures were reduced (12, 15, 18°C), then kept constant, and finally brought back to 25°C (14, 18, and 14 d, respectively). High temperatures proved beneficial to polyp survival and asexual reproduction, yet, in some cases, polyps were able to survive temperatures as low as 12°C. Strobilation occurred at temperatures between 22 and 30°C. Podocyst production, excystment, and strobilation, all take place following a temperature increase, and excystment of podocysts occurs mainly during the first 2 weeks following podocyst production. We propose that the role of podocysts in R. nomadica is to, mainly, increase the current season’s polyp population, contributing to swarm formation, rather than as a means to maintain polyp populations during harsh environmental conditions. Since polyps are able to survive winter temperatures in the western basin (12°C) and reproduce by podocysts and strobilation during summer temperatures (24°C), thermal constraints will probably not restrict the expansion of R. nomadica into the western Mediterranean. Expected future climate change conditions will increase the performance and range expansion of this species.