Effects of deep seawater on the growth of the rhyzostome jellyfish Mastigias papua

Abstract

Rhyzostome jellyfish, Mastigias papua, contain symbiotic dinoflagellates known as zooxanthellae in cells of mesoglea. It is well known that endosymbiotic zooxanthellae are capable of CO2 uptake and fixation and subsequent carbon translocation to jellyfish tissues. To evaluate the effect of deep seawater (DSW) on the growth rates of M. papua medusae, they were reared at 20‒25℃ for 50 days in 3 different waters: DSW, surface coastal seawater from Akazawa Port, Ito, Shizuoka (SCSW), and mixture of equal volume of DWS and SCSW. Survivorship was 100％ for all individuals used in the experiments. The specific growth rate of M. papua reared in the DSW was significantly higher than that observed in the SCSW, suggesting that high-nutrient-containing DSW is effective in carbon fixation of endosymbiotic zooxanthellae, which subsequently enhances the growth rate of host medusae. The density of zooxanthellae in the mesoglea did not show any significant differences among medusa groups reared in the three different seawater types. Hence, it is highly recommended to use the DSW for culturing jellyfish species with symbiotic zooxanthellae, such as upside-down jellyfish Cassiopea spp.