Determination of the ecological quality by posidonia meadows ecosystem in Gökçeada (North Aegean) coastal waters

Posidonia oceanica (Linnaeus) Delile seagrass meadows distribute to wide geographical areas along the infra-littoral zones in the coastal zones of the Mediterranean Sea. However, recent anthropogenic pressures on coastal regions and changing climate conditions have caused irreversible regression and loss of this habitat. Due to its low resilience to the anthropogenic pressures, P. oceanica is used as a bioindicator or 'biological quality element' in long-term monitoring programmes, including in the European Commission's Water Framework Directive (WFD 2000/60/EC) for evaluation of the status of coastal water bodies through ecological modellings. Presence of P. oceanica meadows distributed to wide areas in specific coasts of Gökçeada (North Aegean) under the effect of Turkish Straits Sytem, is very crucial in terms of biodiversity and ecological characteristics of the region and also increases the potential of becoming a "protected area". However the coasts of the island are under the threat of the urbanization, t urism and agricultural activities in the recent years with the population growth. Through this study, the coastal ecosystem status is determined via the conceptual model developed from the ecological and biometric parameters of P. oceanica and its ecosystem components in the sites exposed to different natural and anthropogenic pressures from Gökçeada (North Aegean) in the period of 2016-2018. Furthermore, the ecological indices tested at Western Mediterranean, are adapted to Eastern Mediterranean with the aim of intercalibration and also the relationship between the coastal ecosystem status and the natural and anthropogenic factors is revealed with a multi-disciplinary approach. The ecosystem status (EBQI) and the ecological quality ratio (EQR) of nine different sites around Gökçeada, showed statistical differences (ANOVA, p<0,05). According to the EQR values determined with the descriptive parameters of P. oceanica; Fidanlık (0,62±0,03) is classified as "Good"; Tepeköy (0,46±0,00), Kaleköy (0,43±0,03), Yıldızkoyu (0,41±0,03), Kuzulimanı (0,47±0,02), Güzelcekoy (0,44±0,00), Yüzentaşlar (0,41±0,02) and İncesu (0,49±0,00) are classified as "Moderate" whereas; Kapıkaya (0,32±0,01) is classified as "Poor" status. In terms of the EBQI values determined with the P. oceanica ecosystem functioning; Fidanlık (5,3±0,1), Tepeköy (4,5±0,7) and Yıldızkoyu (4,2±0,1) are classified as "Moderate"; Kuzulimanı (3,7±0,5), Güzelcekoy (3,5±0,1), Yüzentaşlar (4,1±0,4) and İncesu (3,5±0,3) are calssified as "Poor"; Kaleköy (3,3±0,5) and Kapıkaya (3,4±0,1) are classified as "Bad" status. The strong relation (R2=0,6126, p<0,05) between the ecological quality ratios (EQR) and the anthropogenic pressures (LUSI), proved the effectiveness of the Posidonia Biotic Index (BiPo) in determining the ecological status. On the other hand, the less relation (R2=0,3773, p>0,05) between the ecosystem status (EBQI) and the anthropogenic pressures (LUSI), especially reflected the overfishing pressure besides water quality. As can be seen in other studies conducted at a local scale, ecological indices are convenient tools in terms of reliability and feasibility at the Mediteranean scale besides their relevancy in reflecting the anthropogenic pressures. The descriptive ecological and biometric parameters of P. oceanica (lower limit depth and type, meadow density and cover, plagiotrophic rhizomes, rhizome growth, leaf production and foliar surface, shoot length, coefficient A, epibiota biomass) showed statistical differences (ANOVA, p<0,05) both spatially and bathymetrically, therefore we assumed the most important environmental factor affecting the growth of the meadows around the island is "siltation". The decrease of the specific parameters of P. oceanica with the increasing bathymetric slope, put forward the decline of the vitality of the meadows through time. Conservation status, phase-shift and the patchiness of the habitat are approved the hypothesis of "eco-health of P. oceanica is negatively affected from anthropogenic pressures" by showing statistical differences in both shallow and deep zones of four sites; two reference (Fidanlık and Tepeköy) and two anthropized (Yıldızkoyu and Kuzulimanı). The highest conservation index is recorded in the shallow zones of Fidanlık (CI=0,98±0,02) and Tepeköy (CI=0,95±0,03) whereas; the lowest values are recorded in Yıldızkoyu (CI=0,78±0,10) and Kuzulimanı (CI=0,55±0,08), both exposed to tourism pressure. Moreover settlement of Cymodocea nodosa ve Caulerpa racemosa around the roots and rhizomes and their distribution through dead matte areas in Yıldızkoyu (SI=0,01±0,02) and Kuzulimanı (SI=0,02±0,05) with the highest substitution index, creates an important threat for the meadow beds in the future. Also early phase-shift (PSI<0,25) in these sites, could still recover even in the presence of human-induced pressures due to the removal of the principal reasons of regression. It is clear that the coastal ecosystem of Gökçeada (North Aegean) and the ecological status of the P. oceanica meadows are affected from the local anthropogenic pressures (tourism, agriculture, discharges of wastewater) besides natural environmental pressures (hydrodynamism, sedimentation). The ecosystem of the region resists to preserve its natural characteristic structure against to these stress factors. This study contribute to the inventory works of the "coastal conservation and management" plans and also to the sustainibility of the long-term monitoring programmes. Besides, it leads to the "ecosystem based approach" for our coastal waters; therefore more comprehensive researches should be conducted at all Turkish coasts considering the sub biogeographical areas.