The presence of seagrass along the Romanian coast is currently seen as an important component of the marine ecosystem. Moreover, seagrass meadows play an additional wave energy dissipation role that has also to be considered among other ecosystem services. Assessing the impact of a seagrass meadow on the local hydrodynamics is needed to present an integrated protection and adaption plan for discussion with local stakeholders and coastal managers. The impact on wave heights of a possible seagrass meadow, located in front of the barrier beach at the Mangalia marsh on the southern Romanian coast, has been analysed using numerical modelling. Several seagrass configurations have been studied, for low and average wave conditions from various directions. The same waves were used after adding a vegetation mask to the analysed domain, to simulate the presence of a seagrass meadow. The results of the numerical simulations were extracted in several output points, located along three transects crossing the vegetation mask. They show the most significant reduction in the calculated wave energy density during a year of 16.6%, occurring within the seagrass meadow. Our results suggest that, for the southern Romanian coast, seagrass could be introduced in coastal protection plans as an additional measure for wave attenuation. The idea of this work came up following the FP7 RISES-AM project, GA 603396, funded by the FP7-ENV-2013-two stage program of the European Commission. The first author acknowledges the mobility projects MC2017-1274 and MC2018-1922, funded by the Romanian Authority for Scientific Research, covering the expenses of two research visits at the Maritime Engineering Laboratory of the Polytechnic University of Catalonia Barcelona Tech (LIM-UPC), during which work on this topic started. This work was partially supported by the Spanish Government within the Research, Development and Innovation Program through the grant to ECOPLANTS project (Ref. PID2020-119058RB-I00). The REST-COAST Horizon 2020 Research and Innovation Grant 101037097 has also contributed to finance some of the authors. The rest of the work has been performed within the projects PN 18160103 and PN 19200201, funded by the Ministry of Research, Innovation and Digitization of Romania and H2020 DOORS (EC Grant Agreement 101000518). We acknowledge as well the valuable comments of an anonymous reviewer, which allowed us to significantly improve the manuscript. Peer Reviewed