Assessing the Effects of Mussel Aquaculture on Coastal Water Quality Using Sentinel-2 Imagery: An Installation-Based Approach in the Sea of Marmara

Mussel aquaculture is often considered environmentally sustainable due to its potential to filter particles and recycle nutrients, yet its large-scale influence on coastal water quality remains difficult to quantify, especially in complex and highly variable systems such as the Sea of Marmara. Here, an installation-based analytical framework was implemented to evaluate potential mussel farm associations with turbidity and chlorophyll dynamics using Sentinel-2 satellite observations processed in Google Earth Engine. Twenty-one mussel farms in the southern Sea of Marmara were confirmed and digitized from high-resolution Google Earth imagery (most recent imagery year: 2025), and approximate installation years were assigned using time-series imagery interpretation supported by administrative information. Control areas were defined as a 1–3 km ring buffer around each farm to improve interpretability. Turbidity (B3/B2) and the Normalized Difference Chlorophyll Index (NDCI) were derived from annual and monthly median Sentinel-2 surface reflectance composites for 2018, 2020, 2022, and 2024. Annual-scale analyses (ANOVA and linear regression) detected no statistically significant pre- vs post-installation differences (p>0.05) and no significant relationships with time since installation. However, seasonal comparisons during the spring bloom period (March–May) revealed a recurrent negative chlorophyll difference in farm areas relative to controls, although the magnitude was limited and not consistently statistically strong. Overall, results indicate that mussel-related signals in the Sea of Marmara are scale- and season-dependent: patterns that may be consistent with filtration-related processes were more apparent under high-productivity conditions but are largely masked by strong regional variability and mixing, as well as known uncertainties in coastal optical remote sensing.