MEPS:Advance View   -  DOI: https://doi.org/10.3354/meps12204

ABSTRACT: Early-developed polyps of the giant jellyfish Nemopilema nomurai that are sexually produced during the rainy season form the principal recruitment for benthic population stages, regulating the mass outbreaks of medusae that occur in east Asian marginal seas. Their survival, development and subsequent asexual reproduction are likely facilitated by hyposaline seawater and potentially enhanced micro-zooplankton around the estuaries that comprise the major nurseries of medusae. In this study, 8-tentacled polyps that developed from planulae were incubated at 11 salinities from low to high (8, 11, 13, 15, 18, 20, 23, 25, 28, 31, 33) with 3 feeding frequencies (once every 3 d, once every 9 d, unfed; Brachionus plicatilis concentration: 0.16 mg C l^-1) at a constant temperature (19°C). Survival rate of early-developed polyps increased 3-fold at salinities 11 to 20, >80% greater than at salinities 25 to 33. The composition of fully developed polyps, somatic growth, and podocyst diameter positively depended on food supply, except at salinity 8. The potential podocyst production of polyp colonization reached normal peak at salinity 20 in the group that was fed once every 3 d. Excystments were significantly restricted at salinity <20. These findings confirm that estuarine areas with salinities from 11 to 20 are appropriate for N. nomurai polyp colonization, where prospectively increasing micro-zooplankton supply rooted in frequent eutrophication may benefit polyps. An asexual reproduction strategy also corresponded with autumn salinity fluctuations. The intensity of diluted water and monsoonal rainfall, as well as plankton supply around the estuaries in autumn may fundamentally affect polyp abundance and size, determining the population size of medusae in the following spring.

KEY WORDS: Polyps · Low salinity · Survival · Growth · Podocyst reproduction