Neptune Grass

Marine Plant

Identification & Biology

• IdentificationA marine flowering plant (not an alga) with long, ribbon-like green leaves growing from horizontal rhizomes buried in sandy substrate. The leaves form dense underwater meadows. Dead leaf material accumulates as brown, fibrous balls (known as egagropili) washed ashore.
• SizeLeaf length up to 150 cm. Meadows can extend for kilometres.
• Social HabitForms extensive underwater meadows that are among the most important habitats in the Mediterranean. Extremely slow-growing, with meadows taking centuries to develop.
• HabitatSandy and muddy bottoms in clear water with sufficient light. Requires clean, well-lit conditions.
• Depth0 to 40 m. Most productive between 5 and 25 m where light is strongest.
• Feeds OnPhotosynthetic. Absorbs sunlight, carbon dioxide, and dissolved nutrients through its leaves and roots. Produces oxygen.
• DistributionMediterranean Sea only. Endemic to the Mediterranean basin. Found throughout Maltese coastal waters where conditions allow.
• DescriptionPosidonia oceanica is the most important marine habitat in the Mediterranean. Its meadows support over 400 plant and 1,000 animal species, produce vast quantities of oxygen, stabilise sediment, protect coastlines from erosion, and sequester carbon. A single square metre of Posidonia meadow can release up to 14 litres of oxygen per day. The species is strictly protected under EU and national legislation. Meadow regression due to coastal development, anchoring, and pollution is one of the most serious environmental issues in the Mediterranean.