Mapping the National Seagrass Extent of Venezuela

Abstract

Owing to the threats faced by seagrasses in many parts of the world and the knowledge gaps in seagrass extent globally, there is an urgent need to map the global seagrass extent. Venezuela is no exception.

In the Caribbean, Wabnitz et al. (2009) had mapped its regional seagrass extent based on Landsat imagery. However, these are not available or accessible. For Venezuela, the available seagrass data on UNEP-WCMC consists only of point data and the extent maps of two islands, including the Los Rosque Archipelago National Park. Faced with the pressure of the invasive seagrass Halophila stipulacea, it is crucial to know where Venezuela’s seagrasses are, before trying to distinguish where the local and invasive seagrasses are found.

We use an established multitemporal composite approach on Google Earth Engine and Sentinel-2 imagery to map the Venezuelan seagrasses. Reference data were obtained from a mix of ground truth and historical data, curated by expert knowledge. The reference data were split using a 70:30 ratio to obtain 797 training data points and 329 validation data points. Our initial classification achieved an overall accuracy of 76%, which shows the potential of this approach to produce a national extent of seagrasses for Venezuela.