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Sito d'Interesse Comunitario Relitti di Posidonia presso Grado

Identity Card
Cod. RN2000: IT3330008
Surface Area: 0,91 ha
Sea Surface: 100,00 ha
Provinces: GO
  •  (photo by Saul Ciriaco)
  •  (photo by Saul Ciriaco)
  •  (photo by Saul Ciriaco)

The northern limit of Posidonia oceanica in the Mediterranean Sea

In the Gulf of Trieste, Posidonia oceanica constituted vast grasslands forming a wide discontinuous belt from Punta Sdobba to Punta Tagliamento. By the late 1960s, P. oceanica had virtually disappeared from almost the entire Gulf, and witnesses of its relatively recent presence are the subfossil remains (rhizomes). From the 1960s to the present day, P. oceanica has gradually been reduced to "a few tufts" in some areas overlooking the Grado coast. According to CAINER (1993-94) they are "extremely limited formations, not reaching the status of grasslands and therefore representing only small isolated clumps". This is due to climate change, to species sensitivity, to different polluting sources and to the action of turbo-blowers and traction cleats for truffle (Venus verrucosa) and smooth clam (Pitaria chione) fishing. The remaining populations of Posidonia oceanica are found at a depth varying between 3 and 4,5 meters on a hard substrate. Around, on the sandy bottom, instead, there are luxuriant Cymodocea nodosa grasslands. The biological value of this population lies in the fact that it is the northernmost limit reached by P. ocenica and that it has peculiar characteristics as it is monoclonal. The photophilic algal vegetation associated with the Posidonia di Grado leaves refers to the Myrionemo-Giraudietum sphacelarioidis Van der Ben, 1971, while the sciophilous vegetation associated with the rhizomes could be referred to Flabellio-Peyssonnelietum squamariae Molinier 1958. The algal biodiversity associated with Posidonia is relatively high compared to the neighbouring areas (e.g. Grado and Marano Lagoons).

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