The Lungs of the Mediterranean

Posidonia Oceanica

Kali xronia to all! A new year with new perspectives, new challenges, new possibilities. So straighten your spine, pull your shoulders back, raise your chest, take a deep breath and ‘go’! But … that deep breath … some of you will have already felt this one coming … also has a story bound to the overarching theme of our monthly blog; the Mediterranean Sea.

A while back we shared with you the historical significance of the Noble pen shell (Pinna Nobilis) and the sea silk that is produced from its roots. We highlighted the damage that is inflicted to these beautiful, grand shells by ‘randomly’ dropped anchors. The damage is, however, not limited to these shells alone. Indirectly we too are affected. This is why …

Let’s begin with the bigger picture - Mother Earth. Did you know that most of our precious, life-sustaining oxygen comes from the Earth’s oceans? The oceans are home to many ‘freely’ suspended species. Phytoplankton constitute the plant-based of these species and are a vital link in both the food chain and the production of oxygen. Scientists estimate that these little plants produce anywhere between 50 to 85% of the oxygen in the Earth’s atmosphere. Amazing, isn’t it?

Olive of the Sea

Let’s zoom in on the Mediterranean Sea. The Mediterranean is home to another amazing sea plant, the Posidonia Oceanica. Posidonia Oceanica is a sea grass species (not to be confused with sea weed) that you will only find in the Mediterranean and is also the most common species of sea grass in the region. Their name is derived from Poseidon, in Greek mythology the god ruling the seas, the waters and their gods. It is also known as Neptune grass, Mediterranean tapeweed or simply Posidonia. Scientists have established that Posidonia cover anywhere between 25,000 and 50,000 square kilometers of the sea bottom along the Mediterranean coastline. That constitutes roughly 25% of the sea bottom of the Mediterranean Sea within the 0 to 40-meter mark. Posidonia is the most important source of fresh oxygen for the Mediterranean region. According to scientists Posidonia produce between 1 and 20 liters of oxygen per square meter per day. That is almost twice the amount of oxygen produced by a square meter of tropical rain forest per day. That is why Posidonia is also referred to as the lungs of the Mediterranean.

Every year Posidonia bear fruit that require six to nine months to ripen. The likeness of this fruit to another famous Greek product explains it more commonly used nickname ‘olive of the sea’ (see the photo featured on the right hand side).

Posidonia is an incredibly resilient species of underwater flora and has been around for over 100 million years. In fact, the oldest living life form on the planet is a community of Posidonia that was researched in 2012. DNA analysis revealed that patches of a Posidonia community growing between Spain and Cyprus are over 200.000 years old. That makes these patches considerably older than the Tasmanian plant that up until that point held the record with 43.000 years.

Posidonia is, however, not only important for its oxygen production. The sea grass removes large quantities of carbon dioxide from the water. This phenomenon is known as carbon capture and alleviates the effects of climate change.

Posidonia Oceanica Beach Protection

It has also been established that Posidonia plays an important role in the protection of the coastline, both below and above the surface. The ‘living’ sea grass beds absorb the energy of passing waves hence reducing their strength and size as they approach the coastline. This reduces both the speed and severity of coastal erosion. The dead sea grass that washes ashore mixes with the sand forming a buffer against coastal erosion. Both by absorbing the impact of the waves breaking on the shoreline and by the shear weight of the sea grass reducing the mobility of the sand.

Unfortunately, the global surface area covered by Posidonia is declining by a rate of 1-2% per year. That rate of decline is four times faster than the annual rate of decline of tropical rain forests. That is extremely worrying. In the Mediterranean Sea the rate of decline approaches 5% per year. That is simply criminal! Due to the slow growth of Posidonia and their low seed production the losses stated above are pretty much irreversible. The regeneration of sea grass communities takes centuries.

The decline of Posidonia oceanica is almost wholly due to anthropogenic factors (in other words caused by people). The largest impact comes from construction works, trawling (big nets pulled behind fishing boats), pollution of the coastal waters, the use of anchors and artificial beach replenishment. Although Posidonia oceanica is a nationally and internationally protected species in practice that status seems to have little effect on the rate of its decline. Tragic but true.

Should you be a boat owner than please consider carefully where you drop anchor next time. A few meters to the left or right might just make a huge difference.