Posidonia oceanica, a species of seagrass, is often referred to as the “lungs of the Mediterranean” because the seagrass meadows absorb carbon dioxide and output oxygen at twice the daily rate of tropical forests.

Cow bream, Sarpa Salpa, over seagrass in Mediterranean

Cow bream, Sarpa Salpa, over Posidonia oceanica seagrass in the Mediterranean

Seagrasses store an estimated 27.4 million tonnes of carbon each year, burying it in the soil below. And unlike forests that hold carbon for about 60 years then release it again, seagrass ecosystems have been capturing and storing carbon since the last ice age. With seagrass meadows disappearing at an annual rate of about 1.5 per cent, 299 million tonnes of carbon are being released back into the environment each year, according to research published in Nature Geoscience (DOI: 10.1038/ngeo1477).

In addition to storing carbon, seagrasses protect coastlines from floods and storms, filter out sediment, and serve as a vital habitat and nursery for fish, crustaceans and other commercially important species.

Cuttlefish egg on Posidonia oceanica

Cuttlefish egg on Posidonia

In the past century, 29 per cent of seagrass has been destroyed globally by coastal development, fishing by otter-trawling, pollution, and now climate change.

Unique to the Mediterranean Sea, Posidonia beds are identified as a priority habitat for conservation under the European Union’s Habitats Directive (Dir 92/43/CEE) and Catalunya has banned otter-trawling over Posidonia beds. Yet the destruction of this slow growing species continues at an alarming rate.

Nudibranch laying eggs on seagrass

Nudibranch laying eggs on Posidonia

On the Costa Brava, where Kenna Eco Diving has been researching Posidonia for the past 13 years, we have witnessed a loss of an estimated 25 per cent of the Posidonia meadows. Seagrass-friendly moorings for boats are installed during the peak summer months, but boaters are not penalised for anchoring in the Posidonia beds, destroying hundreds of years of growth in minutes.

Barren areas between Posidonia Beds

Barren areas between the Posidonia Beds

As Posidonia meadows are being destroyed the Posidonia pipefish, a relative of the seahorse, is suffering. The Posidonia pipefish is perfectly adapted to the seagrass habitat and has evolved to resemble a blade of seagrass. It is virtually impossible to see unless it swims above or outside the seagrass beds – a rare occurrence as it is a poor swimmer and rarely ventures out of the safety of the Posidonia meadows, spending it’s time head down within the shoots searching for tiny shrimps to eat. It is totally dependent on the Posidonia habitat for daily food and shelter, and as a seasonal breeding ground and nursery.

Syngnathus typhle - the elusive Posidonia pipefish

Syngnathus typhle – the well camouflaged Posidonia pipefish

Posidonia and the pipefish are just two of the key species being studied by volunteer scuba divers assisting Kenna Eco Diving with underwater surveys for the SILMAR Project on the Costa Brava. We are the only voluntary coordinators for the Spanish SILMAR Project working through the English language, opening this volunteering opportunity to international divers who come from all over the world to spend a few weeks or months assisting with the project aimed at conserving Mediterranean biodiversity.

Transect through posidonia beds

Transect through Posidonia beds

Please sign the petition asking for anchoring to be regulated in Posidonia meadows – http://campaign.kennaecodiving.net/campaign-petition.

Photos copyright Gaye Rosier


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