Experiment on pipefish Syngnathus typhle to inhabit low salinity areas of the Baltic Sea

The aim of the study was to investigate the mechanisms allowing pipefish to inhabit low salinity areas of the Baltic Sea. The parental Syngnathus typhle generation for this experiment was caught in seagrass meadows of six sampling sites along the German coastline of the Baltic Sea in spring 2017, i.e. in the Flensburg Fjörd, Falckensteiner Strand, Orth Bay next to Fehmarn, Salzhaff and 2 sample sites around Rügen. Three sampling sites are characterized by relatively high salinity conditions (14 - 17 PSU; high salinity origin; H) and three sampling sites by relatively low salinity conditions (7 - 11 PSU; low salinity origin, L; Table 1). Salzhaff was assigned the category low because salinity drops are common after rainfall accompanied with freshwater discharge due to enclosed morphology of the inlet. Therefore, pipefish in Salzhaff are likely to be exposed to salinity levels below 10 PSU. A minimum of 30 non-pregnant males and 30 females were caught snorkelling with hand nets at each sampling site at depths ranging between 0.5 and 2.5 m. At each sampling site, water temperature and salinity were measured from water collected about 1 m below the surface using a salinometer (WTW Cond 330i). The common garden experiment was conducted at the facilities of the GEOMAR (west shore) in spring 2020.