The effects of temperature and salinity on egg development and settlement of the ascidian Herdmania momus were investigated. Adult specimens were collected from the Dodu Yacht facility in Jeju Island, Korea (33°30′30.54″N, 126°27′55.46″E) in August 2018. Egg development and larval settlement were observed and recorded at 8 h intervals using a stereomicroscope, under nine temperature (10, 13, 16, 19, 22, 25, 28, 31, and 34°C), and four salinity regimens (28, 30, 32, and 34 psu). The highest hatching rate (82.8±7%) was observed at 32 psu and 25°C and the lowest hatching rate (1.0±2%) was at 34 psu and 13°C. The developmental rate (0.222±0.0994) was highest at 28 psu and 28°C, and lowest (0.016±0.008) at 30 psu and 13°C. The highest settlement success rate (77.1±5%) was at 32 psu and 25°C and the lowest (0.1±1.0%) was at 30 psu, and 13°C. The rate of settlement (0.080±0.000) was highest at 28 psu and 28°C, and lowest (0.013±0.000) at 30 psu and 13°C. Both hatching and settlement success rates increased as temperature increased and tended to decrease beyond an optimal temperature range. Herdmania momus preferred 30-34 psu salinity and 22-25°C temperature. This study provides baseline information about the life history of H. momus, and important data to control the damage caused by the increase in number and distribution of this invasive ascidian.

The influx of marine exotic and alien species is disrupting marine ecosystems and aquaculture. Herdmania momus, reported as an invasive species, is distributed all along the coast of Jeju Island and has been confirmed to be distributed and spread to Busan. The potential habitats and distribution of H. momus were estimated using the maximum entropy (MaxEnt) model, quantum geographic information system (QGIS), and Bio-ocean rasters for analysis of climate and environment (Bio-ORACLE), which can predict the distribution and spread based only on species occurrence data using species distribution model (SDM). Temperature and salinity were selected as environmental variables based on previous literature. Additionally, two different representative concentration pathway (RCP) scenarios (RCP 4.5 and RCP 8.5) were set up to estimate future and potential habitats owing to climate change. The prediction of potential habitats and distribution for H. momus using MaxEnt confirmed maximum temperature as the highest contributor (77.1%), and mean salinity, the lowest (0%). And the potential habitats and distribution of H. momus were the highest on Jeju Island, and no potential habitat or distribution was seen in the Yellow Sea. Different RCP scenarios showed that at RCP 4.5, H. momus would be distributed along the coast of Jeju Island in the year 2050 and that the distribution would expand to parts of the Korea Strait by the year 2100. RCP 8.5, the distribution in 2050 is predicted to be similar to that at RCP 4.5; however, by 2100, the distribution is predicted to expand to parts of the Korea Strait and the East Sea. This study can be utilized as basic data to effectively control the ecological injuries by H. momus by predicting its spread and distribution both at present and in the future.