169 J. Black Sea/Mediterranean Environment Vol. 30, No. 3: 169-182 (2024) RESEARCH ARTICLE An ecological study on Posidonia oceanica (Linnaeus) Delile, 1813 meadow in Rachgoun Island (Algerian west coast, Mediterranean Sea) Adnane Mahmoud Benallal 1 , Ahmed Kerfouf 1* , Ali Becheker 2,3 , Patricio R. de los Ríos-Escalante 4,5 , Denis Françoise 6 ORCID IDs: A.M.B. 0009-0005-1778-0028; A.K. 0000-0002-4466-1201; A.B. 0000- 0003-2937-6768; P.D.L.R. 0000-0001-5056-7003; D.F. 0000-0002-0006-8238. 1 Laboratory of Eco-development of Space, University of Djillali Liabes, Sidi Bel Abbès, 22000, ALGERIA 2 Environment and Biodiversity Research Division, Environmental Research Center, Annaba 23000, ALGERIA 3 Environmental Research Center, BP 72 A Menadia Annaba, 23000 Annaba, ALGERIA 4 Departamento de Ciencias Biológicas y Químicas, Facultad de Recursos Naturales, Universidad Católica de Temuco, Casilla 15-D, Temuco, CHILE 5 Núcleo de Estudios Ambientales UC Temuco, CHILE 6 Le Mans University- Laboratory BOREA MNHN, CNRS 8067, SU, IRD 207, UCN, UA- Concarneau, FRANCE * Corresponding author: kerfoufahmed@yahoo.fr, ahmed.kerfouf@univ-sba.dz Abstract Posidonia oceanica is an endemic species of the Mediterranean Sea, but recently it is actually exposed to anthropogenic pressures by numerous activities of various origins (coastal developments, trawling, anchoring, turbidity, erosion and beach nourishment). The aim of this study is to evaluate the ecological status of P. oceanica meadows around Rachgoun Island of Algerian west coast. The entire island is protected according to the Ramsar Convention and a marine protected area in the process of being classified. The ecological study revealed that the density values reveal a dense to sparse meadow, and the cover rates are among similar values on the Algerian coasts, between 70 % and 88.32%. The analysis carried out on structural features shows that these parameters are strongly influenced by multiple factors (depth, hydrodynamics and anthropogenic actions). The biometric parameters and phenological study (length and width of leaves, leaf surface, coefficient A and leaf area index) of P. oceanica show that the Rachgoun Island meadows are, globally, in good health status. Keywords: Posidonia oceanica, ecological status, marine protected area, phenological study Received: 23.10.2024, Accepted: 21.12.2024