Acclimation potential of the invasive sea anemone Haliplanella lineata (Verrill 1898) to changing salinities

We detected a successful establishment of the Japanese sea anemone H. lineata in Kiel Fjord. The cosmopolitan actinian has successfully invaded multiple ecosystems around the world. The introduction of invasive species poses a threat to the native communities and may also cause economic problems. Invasive species are known to possess wide physiological tolerances of abiotic stressors, which enables them to survive transport and facilitates settlement. For invaders to the Baltic Sea one of the most challenging factors is the salinity gradient. The degree of euryhalinity of this osmoconforming organism therefore determines its geographic distribution. To study the invasion success of H. lineata in relation to salinity we assessed anemone growth and asexual reproduction as fitness proxies during a 4-week acclimation period to salinity levels representing environmental conditions that can be encountered in the Western Baltic Sea & North Sea (7, 14, 24 and 34 PSU). We assessed salinity dependent energy budgets using feeding rate, oxygen consumption and ammonium excretion to determine the Scope for Growth. An NMR-based metabolomic approach was used to analyse intracellular osmolyte composition. H. lineata exhibited a rapid - 5-fold - population growth at salinities of 24 and 34 PSU within 4 weeks. Euhaline salinities of 24 and 34 PSU seem to provide significantly better conditions in terms of biomass growth (0.53±0.09, 0,54±0.15 mg day-1, respectively) and fission rate (2.14±0.41 and 1.96±0.64 fission week-1, respectively) than animals maintained at 14 PSU (1.39±0.48 fission week-1). Anemones acclimated to 7 PSU did not reproduce asexually, moreover their biomass decreased. They further exhibited significantly lower respiration rates implying a state of metabolic depression. Feeding rate significantly increased at 14, 24 and 34 PSU compared to 7 PSU. Further, feeding rate at 34 PSU was significantly higher compared to 14 PSU. However, the energy budget calculations demonstrate that large amounts of energy are unaccounted for. This is most likely due to differences in absorption efficiencies, DOM leakage, anaerobic processes or mucus production. Betaine, dimethyl sulfone, glycine, homarine and taurine were identified as the five major osmotically active solutes. Betaine made up the largest fraction (40 %) and experienced the strongest changes in relative abundance with changing salinity (0.01±