Using the critical salinity (Scrit) concept to predict invasion potential of the anemone Diadumene lineata in the Baltic Sea

It is widely assumed that the ability of an introduced species to acclimate to local environmental conditions determines its invasion success. The sea anemone Diadumene lineata is a cosmopolitan invader and shows extreme physiological tolerances. It was recently discovered in Kiel Fjord (Western Baltic Sea), although the brackish conditions in this area are physiologically challenging for most marine organisms. This study investigated salinity tolerance in D. lineata specimens from Kiel Fjord in order to assess potential geographical range expansion of the species in the Baltic Sea. In laboratory growth assays, we quantified biomass change and asexual reproduction rates under various salinity regimes (34: North Sea, 24: Kattegat, 14: Kiel Fjord, 7: Baltic Proper). Furthermore, we used 1H-NMR-based metabolomics to analyse intracellular osmolyte dynamics. Within 4 weeks D. lineata exhibited a 5-fold population growth through asexual reproduction at high salinities (34 and 24). Biomass increase under these conditions was significantly higher (69%) than at a salinity of 14. At a salinity of 7, anemones ceased to reproduce asexually, their biomass decreased and metabolic depression was observed. Five main intracellular osmolytes were identified to be regulated in response to salinity change, with osmolyte depletion at a salinity of 7. We postulate that depletion of intracellular osmolytes defines a critical salinity (Scrit) that determines loss of fitness. Our results indicate that D. lineata has the potential to invade the Kattegat and Skagerrak regions with salinity >10. However, salinities of the Baltic Proper (salinity <8) currently seem to constitute a physiological limit for the species.学界普遍认为，外来物种对本土环境的适应能力决定了其入侵成功与否。纵条矶海葵（Diadumene lineata）是一种广布性入侵物种，具备极强的生理耐受能力。该物种近期在波罗的海西部的基尔峡湾（Kiel Fjord）被发现，尽管该区域的半咸水环境对多数海洋生物而言具有生理胁迫性。本研究针对采自基尔峡湾的纵条矶海葵样本开展盐度耐受实验，以评估该物种在波罗的海的潜在地理扩张范围。在实验室生长实验中，我们对不同盐度处理组（34：北海、24：卡特加特海峡、14：基尔峡湾、7：波罗的海本部）下的生物量变化与无性繁殖速率进行了定量分析。此外，我们采用基于氢谱核磁共振（1H-NMR）的代谢组学技术分析了细胞内渗透调节物质的动态变化。在高盐度条件（34与24）下，纵条矶海葵通过无性繁殖在4周内实现了种群数量5倍增长。该条件下的生物量增幅（69%）显著高于盐度14组。而在盐度7的条件下，海葵停止无性繁殖，生物量下降，并出现代谢抑制现象。研究共鉴定出5种主要的细胞内渗透调节物质，其表达会随盐度变化发生调控，且在盐度7时出现渗透调节物质耗竭。我们推测，细胞内渗透调节物质的耗竭会界定一个临界盐度（Scrit），该临界值决定了物种适合度的丧失。研究结果表明，纵条矶海葵具备入侵盐度大于10的卡特加特海峡与斯卡格拉克海峡区域的潜力。但目前波罗的海本部盐度低于8的水环境，似乎构成了该物种的生理极限。