The effects of temperature, salinity, food and predation on the invasive hydrozoan, Moerisia lyonsi, were studied in the laboratory to understand its cross-oceanic distribution patterns and the quantitative relationships between the asexual reproduction of polyp and medusa buds. Polyp mortality occurred only at some treatments of salinities 35-40. Polyps reproduced asexually at salinities 1-40 at 20-29°C, but not at 10°C. The highest asexual reproduction rates occurred at salinities 5-20 without significant difference among salinities. The scyphomedusa, Chrysaora quinquecirrha, was found to prey heavily on the medusae of M. lyonsi and may have restricted its distributions in estuaries. The initiation and proportion of medusa bud production was more responsive to environmental changes than that of polyp bud production. Unfavorable conditions enhanced polyp bud production, while favorable conditions enhanced medusa bud production. The adaptive reproduction processes of M. lyonsi and the significance to survival and dispersal of the populations are discussed.