The Posidonia Oceánica is an endemic aquatic plant of the Mediterranean Sea. They are not algae; they are plants with flowers adapted to the sea floor.

Located in the sandy bottoms of Las Rotas and Las Marinas, the sea grass prairies provide high ecological value to the marine environment, coasts and beaches. They constitute a major green lung for the Mediterranean Sea - 1 m2 produces 10 liters of oxygen a day -. In addition, it provides shelter to a large variety of animal and plant organisms.

The Posidonia remains on the beach, with their roots and leaves, retain the sand and protect the beaches from erosion, hence it is not convenient to continually remove them. They are considered as a good bioindicator of the quality of the coastal sea water.

The Posidonia seagrass prairies are priority habitats and are protected by the EU, national and Valencian Community legislation.