Modeling of Eucheuma cottonii habitat suitability in relation to upwelling and the Indian Ocean Dipole in Cilacap and Kebumen Coastal Waters, Indonesia

This study examines the influence of climate variability associated with the Indian Ocean Dipole (IOD) on the habitat suitability of E. cottonii cultivation in the coastal waters of Cilacap and Kebumen, southern Java. A Habitat Suitability Index (HSI) model was developed using a Boolean threshold implemented in Python. Environmental parameters included sea surface temperature (SST), salinity, nitrate concentration, surface current velocity, and bathymetry. The analysis focused on three representative years reflecting different climate conditions: negative IOD (2016), normal conditions (2018), and positive IOD (2019) from June–September. Results indicate that seasonal upwelling in southern Java tends to reduce habitat suitability for E. cottonii. During normal and positive IOD conditions, stronger upwelling from July to September corresponded with lower HSI values compared with June. In contrast, during the negative IOD phase, when upwelling signals were weaker, HSI values remained relatively stable. Kruskal–Wallis results indicate significant differences in SST, salinity, and nitrate among climate conditions, whereas surface currents show no significant variation. Sensitivity analysis suggests that bathymetry contributes more strongly to habitat suitability, while other parameters vary under different IOD conditions. Because the analysis is based on only three representative years, the results should be interpreted as exploratory rather than a generalized climatic pattern.