Long-term assessment of ecological change in Izmir Bay using abiotic and biotic indicators within a tipping point framework
Regional Studies in Marine Science, cilt.99, 2026 (SCI-Expanded, Scopus)
- Yayın Türü: Makale / Tam Makale
- Cilt numarası: 99
- Basım Tarihi: 2026
- Doi Numarası: 10.1016/j.rsma.2026.105124
- Dergi Adı: Regional Studies in Marine Science
- Derginin Tarandığı İndeksler: Science Citation Index Expanded (SCI-EXPANDED), Scopus, BIOSIS, Zoological Record
- Anahtar Kelimeler: ALEX index, Benthic degradation, Dissolved oxygen, Ecosystem instability, Eutrophication, Izmir Bay, TUBI
- Dokuz Eylül Üniversitesi Adresli: Evet
Özet
Izmir Bay, one of the most heavily impacted semi-enclosed basins of the eastern Mediterranean, has experienced long-term nutrient enrichment and organic loading that threaten ecosystem stability. This study evaluates long-term summer observations collected between 2008 and 2025 by integrating dissolved oxygen (DO), ammonium (NH₄–N), nitrate + nitrite (NOₓ-N), ortho-phosphate (o.PO₄–P), and total organic carbon (TOC) with benthic bioindicator indices (TUBI and ALEX) to assess ecosystem change along the bay’s environmental gradient. The results reveal pronounced spatial contrasts across the bay. The Inner Bay is characterized by high TOC and ammonium accumulation, persistent hypoxia, elevated NOₓ concentrations, degraded benthic conditions (low TUBI), and strong invasive-species pressure (high ALEX), indicating chronic ecological stress and reduced ecological resilience. In contrast, the Outer Bay maintains relatively stable oxygen conditions, lower nutrient levels, and healthier benthic communities, although occasional influence from the Gediz River is evident at Station 3. The Middle Bay shows intermittent extremes in nutrients, TOC, dissolved oxygen, and biotic indices, suggesting increasing ecological instability and possible threshold-like ecosystem responses. Correlation analyses revealed strong relationships between TOC, ammonium, and benthic degradation patterns, although these associations do not necessarily imply direct causality. NOₓ appeared as a secondary indicator of nutrient imbalance. Benthic responses to dissolved oxygen exhibited non-linear response patterns potentially associated with ecological stress gradients. Reported fish mortality events in 2024 coincided temporally with severe oxygen depletion and nutrient anomalies in the Inner Bay, providing additional observational evidence of heightened ecological stress and increasing ecosystem vulnerability in this part of the bay. Beyond the regional case study, the integrated use of abiotic and biotic indicators provides a transferable framework for identifying potential signals of ecosystem instability in semi-enclosed coastal systems. Such assessments can support ecosystem-based management and long-term monitoring of Mediterranean and other coastal environments experiencing similar anthropogenic pressures.