Effects of salinity on seed germination and early seedling growth of the Mediterranean seagrass Posidonia oceanica (L.) Delile

Previous research has demonstrated the low tolerance of Posidonia oceanica mature shoots to salinity variability but there is no information about the response of its seeds and seedlings to this impact. In the present study, two independent experiments were conducted to investigate the effects of salinity variation on germination, development and survival of P. oceanica seeds and seedlings under laboratory-controlled conditions. Maximum P. oceanica seed germination occurred at the control salinity (37), while mortality was lowest for this treatment. However, no significant differences were detected with other salinity levels (39–49). In contrast, salinity appears to play an important role in seedling development. The number of blades, the length of the primary root and the maximum length of leaves of seedlings were significantly reduced with increased salinities. The results observed in the present study are consistent with those obtained for mature P. oceanica shoots, and suggest that hypersalinities, such as those associated with brine discharge of a desalination plant, may limit P. oceanica seedling recruitment, affecting the expansion and recovery of Posidonia meadows.