Distribution and status of Posidonia oceanica meadows on the North-Western coast of Algeria

Posidonia oceanica is an endemic species of the Mediterranean Sea that in pristine coastal waters forms extensive meadows,which are, actually, exposed to natural and anthropogenic pressures, causing their regression throughout the basin. The aim of ourstudy is to summarise and evaluate current knowledge about the characterisation of Posidonia oceanica along the Western Algeriancoast, in order to provide new evidence about the distribution and health status this species. To realize our objectives, we combinedextracted data from published articles, theses, results of project reports, in situ observations and laboratory analysis. The results showthe presence of the meadows in fifteen coastal zones of Western Algeria, mainly located in shallow surface waters from 0.5 to18metres depth.The mean leaf length across all sites ranged from 153 to 667 mm. The mean number of leaves/shoot ranged between4.7 ± 0.9 and 6.0 ± 0.5 leaves/shoot. Leaf length showed a highly significant difference between the cold and hot season. The dataanalysis shows that the leaf biometric values and the shoot densities of the P. oceanica are greater than those of Mediterranean samples although these measures tend to decrease deeply. The analyses carried out on structural features of P. oceanica show that theWestern Algerian meadows are, globally, in good health status according to standardised scale. The available data on P. oceanicasummarised in this article represent an important starting point to build effective plans for understanding levels of environmentalthreats and for supporting conservation strategies for these important ecosystems. Conversely, the limited information available onthis seagrass along the Western Algerian costs only allows the description of some structural features, and permits us to draw overallconclusions on its general health status.