Global relationship between upwelling intensities and mangrove distribution and area

Mangroves are essential coastal ecosystems distributed across tropical and subtropical regions, typically found at the confluence of river systems and the sea. Although air temperature has long been recognised as a key determinant of mangrove distribution, upwelling systems that transport cold, nutrient-rich waters from the deep ocean to the surface can also impede mangrove propagule dispersion. However, global studies that examine the influence of upwelling on mangrove distribution remain scarce. In this study, our objective was to investigate the relationship between upwelling systems and global mangrove distribution, with an emphasis on range limits and area extent. We adopted a novel multi-scale approach by analysing mangrove areas at several minimum size thresholds (≥5 ha, ≥50 ha, ≥100 ha, ≥200 ha, and ≥ 300 ha) to evaluate the scale dependence of upwelling effects. Our regression models revealed a clear trend: the coefficient of determination (R²) increased from 0.20 for patches ≥5 ha to 0.37 for ≥50 ha, 0.43 for ≥100 ha, 0.49 for ≥200 ha, and reached 0.53 for patches ≥300 ha. Furthermore, low-upwelling regions harbour 47.7 % of the total mangrove area (66,763 km²), whereas high-upwelling regions account for only 0.5 % (2642 km²). We also found that the highest upwelling intensities occur exclusively in the Atlantic East Pacific mangrove region, a key environmental contrast to the Indo-West Pacific. In conclusion, our study demonstrates that upwelling systems are one factor shaping global mangrove distribution in a strongly scale-dependent manner, with larger, contiguous patches exhibiting a markedly stronger response. These insights emphasise the need to incorporate upwelling intensity and spatial scale into global mangrove conservation and management strategies. This integration is essential to address the complex interplay of environmental factors under shifting oceanographic and climatic conditions.