Effects of temperature on the reproduction type of Scolionema suvaense living on seaweed and seagrass

Abstract

Scolionema suvaense is a medusa belonging to the order Limnomedusae, and commonly lives on seaweed and seagrass. The benthic polyp and planktonic medusa are both stages of the life cycle of S. suvaense. Most of the planulae produced by sexual reproduction by the medusae do not metamorphose into polyps but to motile frustules moving to the bottom, which then metamorphose into polyps. The polyps can asexually produce not only medusae but also motile frustules. At a low temperature (15°C), polyps mostly asexually produce frustules. Extension of the habitat area by motile frustules is suggested to occur during winter and early spring when the temperatures are low. With increasing temperature, the reproduction type of S. suvaense polyps changes to asexual production of medusae. In the medusa stage, S. suvaense can reproduce both sexually and asexually. The relative percentages of asexually-reproducing medusae vs. sexually-reproducing medusae were highest at 20°C. This coincides with the highest abundance recorded for S. suvaense medusae, which showed an abrupt increase between May and June. Moreover, with increasing temperature (over 25°C), the reproductive mode of S. suvaense medusae changes from asexual to sexual, and asexually reproducing medusae are not observed at such high temperatures. Changes in the reproduction type and fluctuations in the subsequent population dynamics of S. suvaense depend on the in situ temperatures.