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To invade or not to invade: Impaired larval development at low salinities could limit the spread of the non-native crab Hemigrapsus takanoi in the Baltic Sea

Ola Mohamed Nour*, Christian Pansch, Mark Lenz, Martin Wahl, Catriona Clemmesen, Meike Stumpp

*Corresponding author:

ABSTRACT: The Asian shore crab Hemigrapsus takanoi, which is native to the north-west Pacific Ocean, was recently discovered in the Kiel Fjord (south-western Baltic Sea). In laboratory experiments, we tested the salinity tolerance of H. takanoi across eight salinity levels (0 to 35) and across three life-history stages (larvae, juveniles and adults) to assess its future potential to invade the brackish Baltic Sea. Larval development at the different salinities was monitored from hatching to the megalopa stage, while survival and feeding of juveniles and adults were assessed over 17 days. Larvae of H. takanoi were able to complete their development to the megalopa at salinities ≥ 20 and the time needed from hatching to reaching this stage did not differ between salinities of 20, 25, 30 and 35. At a salinity of 15, larvae still reached the last zoea stage (Zoea V), but the development to the megalopa was not completed. All juveniles and all adults survived at salinities from 5 to 35. Feeding rates of juveniles and adults increased with increasing salinity across the entire salinity range. However, feeding rate of adults reached its maximum between salinities 15 and 35. Our results indicate that both juveniles and adults of H. takanoi, are euryhaline and can tolerate a wide range of salinity, at least for the time period tested (2 weeks). However, larval development was impaired at salinities lower than 20, which may prevent the spread of H. takanoi into the Baltic Proper.