<i>In situ</i> study of environmental factors (temperature and salinity) affecting cohort patterns and growth rates in <i>Ciona robusta</i>

Assessing and understanding the ecological impacts of marine invasive species is important for managing marine ecosystems, especially since their rapid growth, short reproductive cycles, and wide range of water temperature adaptability pose major challenges. In this study, conducted in Mokpo, South Korea, we explored the cohort dynamics and environmental influences on the ascidian <i>Ciona robusta</i>, which is considered a widespread invasive species. Through biweekly field surveys and quantitative measurements (dry weight, wet weight and body length) conducted from June to October 2022, we identified five distinct cohorts, challenging existing assumptions about lifespan and cohort patterns. All separation index value (which quantify differences between cohorts) exceeded 2, indicating clear separation of cohorts during the study period. The cohorts had a lifespan of between 4 and 10 weeks, much shorter than the previously reported maximum of 2 years. These differences suggest that local climatic conditions can have a significant impact on lifespan parameters. In addition, growth rates were significantly positively correlated with environmental conditions, particularly temperature. This highlights that while <i>C. robusta</i> growth rates are particularly sensitive to temperature changes, they showed relative tolerance to the salinity variations observed in this study. Therefore, this study contributes to the understanding of the population ecology of <i>C. robusta</i> in temperate marine ecosystems. In particular, it provides valuable insights for developing management strategies to mitigate the impacts of <i>C. robusta</i> due to climate change.