Abstract
Abstract. Sargassum is a brown seaweed distributed in the Philippines and recognized as an additional source of income for fishing communities. Due to uncontrolled harvesting of the seaweed, the Department of Agriculture regulated its collection and harvesting by imposing seasonal restrictions. Hence, the need to identify the locations and cover of healthy Sargassum is vital to address the demand in the market while maintaining ecological balance in the marine ecosystem. Two Sentinel-2 satellite imagery (10 m resolution) acquired on December 08, 2017 (peak growth) and May 27, 2018 (senescence stage) were used to map the presence of Sargassum in the eastern coast of Southern Leyte. Supervised classification using maximum likelihood algorithm and accuracy assessment were conducted before generating the map. Three classes were considered namely Sargassum, clouds and land. Furthermore, Anselin Local Moran’s I (cluster and outlier analysis) was conducted to determine which areas have significant clustering of “healthy” Sargassum using the normalized difference vegetation index (NDVI). For both image dates, high classification accuracies of Sargassum were obtained in the islands. However, there are misclassifications of Sargassum in Silago (UA = 78.72%) and Hinunangan (PA = 82.35%) using the May image. Furthermore, misclassification of Sargassum were obtained in Silago (PA = 93.6%) and Hinundayan (PA = 96.23%) using the December image. Clusters of high NDVI values are more evident in December. Healthy Sargassum are apparent in the coast of Silago and mostly found near shore and in rocky substrates.
Highlights
1.1 Background of the StudyThe genus Sargassum is one of the important brown seaweeds that is distributed in temperate and tropical oceans
The study area limits its extent to 500 m offshore due to the inability of the seaweed to grow beyond the set distance. The coastline of these municipalities were used as the study area because, naturally growing Sargassum are present in the area
Top Of Atmosphere (TOA) reflectance is a combined surface and atmospheric reflectance in order to reduce the in between-scene variability through a normalization for solar irradiance (Congedo 2016)
Summary
The genus Sargassum is one of the important brown seaweeds that is distributed in temperate and tropical oceans It is utilized as animal feed, fertilizer, and as source of alginate which has various industrial uses. It is a promising raw material for ethanol production because of its relatively high content of holocellulose (Tamayo and Del Rosario 2014) It provides food, refuge and breeding grounds for fish, sea turtles, marine birds, crabs, shrimps and more. MERIS stopped functioning in 2012 MODIS alternative floating algae index (AFAI) was used to continually monitor the distribution of the seaweed in the Caribbean, the greater Intra-Americas. Geostatistical analysis was conducted to determine the locations of healthy Sargassum within the study area as a tool for Sargassum resource management
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