Mapping the relocation and expansion of Kappaphycus alvarezii cultivation units based on rainfall and sea surface temperature from high and low resolution satellite data in Bone Bay, Indonesia

Abstract

Climate variability increases the pressure on the sustainability of seaweed cultivation in tropical regions. This study aimed to analyse the dynamics of relocation and expansion of Kappaphycus alvarezii cultivation in Bone Bay, Indonesia, by integrating high-resolution multitemporal PlanetScope imagery with sea surface temperature (SST) and rainfall data obtained from MODIS and CHIRPS during the period 2022–2024. An Object-Based Image Analysis (OBIA) approach combined with the Random Forest algorithm was applied to map the spatial distribution of cultivation areas and quantify temporal changes in the area and number of cultivation units. Classification results showed consistent performance with a moderate level of accuracy, with overall accuracy values ranging from 68.4% to 72.5% and Kappa coefficients between 0.58 and 0.67, indicating that high-resolution optical imagery is capable and temporally stable in detecting seaweed cultivation areas in complex coastal environments. Temporal analysis revealed clear seasonal and interannual variability, with a tendency for cultivation area expansion during the monsoon transition period (March–September) and contraction during the rainy season (October–December). Statistical analysis showed a consistent negative relationship between increasing sea surface temperature and the area and number of cultivation units, whereas rainfall only had a positive effect at moderate intensity levels. This study confirms the novelty of an integrative approach between high-resolution satellite imagery and climate variables as a basis for developing a seaweed cultivation management system that is adaptive to future climate variability and changes.

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