Biodiversity: The importance of Neptune grass
Did you know that Neptune grass‚ or Posidonia oceanica‚ is not a seaweed but a plant?
The Neptune grassland‚ nowadays almost disappeared in the areas affected by the presence of anthropic activity‚ is abundantly present inside the Marine Protected Area of Capo Gallo - Isola delle Femmine and Ustica‚ occupying extensive surfaces and offering shelter to a considerable quantity of animal species and plants. The MPA offers excellent conditions for the settlement and development of neptune grass‚ representing an ideal habitat for the growth of this very important plant‚ endemic to the Mediterranean sea.
Seagrasses are much more complex plants than the algae they are often confused with. Originated from land plants‚ about 100 million years ago‚ they evolved with special adaptations to develop in the marine environment.
Like terrestrial plants‚ neptune grass also has real roots‚ stems (called rhizomes) and leaves‚ on average just over one meter long and about one centimeter thick and are therefore characterized by organs with specialized tissues for the absorption and transport of water and nutrients‚ as well as for the synthesis and accumulation of photosynthetic products.
The rhizomes‚ which can grow horizontally (plagiotropic) or vertically (orthotropic)‚ undergo a process of lignification that prevents decomposition even for hundreds of years.
During our dives‚ we can see that these plants grow on so called “mats”‚ a terraced formation consisting of a set of rhizomes and sediments trapped by the leaves themselves‚ which can reach considerable dimensions. In this way the neptune grass meadows can colonize an environment that is difficult to use by algae due to their lack of roots.
Neptune grass reproduces sexually‚ with the formation of hermaphrodite flowers and fruits‚ and also through sexual development with a growth of stolons. The fruit‚ commonly called "sea olive"‚ reaches maturity between March and May. It then detaches from the plant and due to the presence of oily substances‚ it floats. Dragged by the currents it moves until it rots‚ deposits the seeds on the bottom‚ where they sprout if they find suitable conditions for development.
The meadow of neptune grass has a great importance for the balance of the coasts and the marine environment‚ so much to be considered a "bioindicator": its presence indicates in fact a moderate intensity of the currents‚ a remarkable transparency of the water column and excellent biochemical conditions of the waters in which it has settled.
We usually can admire the beautiful green neptune grass fields during our dives‚ as these plants live between 1 and 30 meters of water depth and tolerates temperatures between 10 and 28 degrees centigrade. It is a plant that needs constant salinity values and strong lighting (limiting factors).
In autumn‚ when diving‚ we can see that the neptune grass loses its outer leaves‚ which become brown and are photosynthetically inactive. Once detached‚ they play an important role in protecting the coast from the waves‚ reducing the phenomenon of erosion: the leaves torn from the winter storms are deposited by the waves on the coasts where‚ piling up‚ they form structures that take the name of "banquette".
Underwater‚ every part of the neptune grass plant is colonized by plant and animal organisms. On the leaves it is possible to observe brown and red encrusting or filamentous algae‚ together with many bryozoans and hydrozoans (slender feathered structures). Adapted to low light intensity are the organisms that live adhered to the substratum of the Posidonia oceanica‚ consisting of leaves and rhizomes. But also some vagile organisms‚ that is‚ capable of moving inside the prairie can be found here: among these the most present are the echinoderms such as the sea urchin and the starfish. Among the molluscs‚ the habitual and almost exclusive inhabitant of the prairies is Pinna nobilis‚ the largest bivalve in the Mediterranean Sea‚ but hard to find nowadays when diving‚ since it is strongly threatened by fishing and pollution.
The netpune grass fields are also a fundamental nursery where not only fish species but mollusc shellfish and many other organisms find protection for reproduction and growth.
Curiously‚ the genus Posidonia‚ next to the Mediterranean‚ is found exclusively along the southern and western coasts of the Australian continent. The Posidonia is among the most important ecosystems of the Mediterranean Sea (climax community) and has been indicated as a "priority habitat" that must be protected.
All PADI scuba diving courses are aimed at protecting these ecosystems. From your PADI Open Water Diver Course up to scuba diving courses like the PADI Advanced Open Water Diver or PADI Deep Diver‚ at our dive resort Evasioni Blu Diving‚ you have the opportunity to explore wonders like the fields of neptune grass in the Marine Protected Area of Isola delle Femmine and Ustica. But even more interesting is knowing how to identify the different marine animal and plant species with the PADI AWARE –Fish Identification or PADI Underwater Naturalist Diver specialty certifications.
Did you know…?
• In the past the leaves were used as an insulator in the construction of roofs and in pharmacology to treat inflammation and irritation.
• In 2OO6 a Posidonia plant about 8 km in length was discovered in the Balearics‚ to which an age of 1‚000 years was attributed. The plant was located inside a prairie that extends for 7OO square km‚ from the area of Es Freus (Formentera) to the beach of Las Salina (Ibiza).
The importance of Posidonia:
• Thanks to its leaf development it frees up to 20 liters of oxygen a day for every square meter of grassland.
• It produces and exports biomass both in the neighboring ecosystems and in depth.
• It offers shelter and is a breeding area for many fish‚ cephalopods‚ bivalves‚ gastropods‚ echinoderms and tunicates.
• It consolidates the seabed below the coast‚ helping to counteract the excessive transport of thin sediments from the coastal currents.
• It acts as a barrier that dampens the force of currents and waves preventing coastal erosion.
• The damping of the wave movement caused by the layer of dead leaves on the beaches protects them from erosion‚ especially during the winter storms.
