EUROPA – Underwater flora and fauna,Posidonia

Posidonia (Posidonia oceanica) is a seagrass with dark green, meter-long leaves that grow in tufts from the tips of its intertwined branches. The branches grow only one centimeter per year and are often covered in sediment, sometimes in meters-long layers. Such branches began growing thousands of years ago, making Posidonia one of the longest-living organisms on Earth! The scientific genus name Posidonia was given after Poseidon, the Greek god of the sea. The species name oceanica was given to it by the renowned biologist Carl Linnaeus because he thought it lived in oceans. However, Posidonia is an endemic Mediterranean organism and its closest relatives inhabit the seas of Australia. Like terrestrial flowering plants, Posidonia reproduces through the process of flowering, which includes both male and female flowers. It blossoms at regular annual intervals and the unattractive green inflorescence blossoms during the autumn. Sometimes few can be found, while at other times, the inflorescence can be found in each of the hundreds of tufts on the surface of a square meter. After fertilization with thread-like and sticky pollen, which is carried by the sea, a fruit that looks like an olive develops. In the spring the fruit ripens, detaches itself from the stalk and floats on the surface for several days. When it bursts, a seed falls out and sinks to the bottom. If it sinks to the bottom at depths shallower than 40 meters which has enough light for the development of Posidonia, it will begin the process of slow growth. Through creeping growth and the branching of branches, over the course of decades, a settlement with a diameter of only a few meters will develop. Over the centuries, it may expand to encompass part of a smaller bay. It will take millennia for the settlement to reach the proportions that Posidonia has in the Croatian seabed today. Because of its extremely slow growth, any destruction of its smallest settlements is irreparable within the timeframe of a human lifespan. The settlements of Posidonia are inhabited by numerous organisms and are considered areas with the greatest biodiversity of the Mediterranean Sea as well as areas with the greatest organic production. Its leaves purify the water column and after they fall off, they accumulate on the shore as lažina (accumulated dry sea grass on a sandy shore) where during the winter they protect sandy beaches from erosion caused by waves. In its settlements in Croatia, a fish named picarel has been traditionally caught for centuries. Its leaves are even today used for making mattresses and pillows and its buried branches permanently store carbon, consequently reducing the impact of global warming. When you are near the sea, take a deep breath because you'll inhale the oxygen produced by the most important plant of the Mediterranean Sea: Posidonia. Dr. sc. Ante Žuljević