Posidonia oceanica

Posidonia oceanica, commonly known as Neptune grass or Mediterranean tapeweed, is a seagrass species that is endemic to the Mediterranean Sea. It forms large underwater meadows that are an important part of the ecosystem. The fruit is free floating and known in Italy as "the olive of the sea" (l'oliva di mare). Balls of fibrous material from its foliage, known as egagropili or Neptune balls, wash up to nearby shorelines. Posidonia has a very high carbon absorption capacity, being able to soak up 15 times more carbon dioxide every year than a similar sized piece of the Amazon rainforest....read more on Wikipedia.