An Analysis on the Biophysical Conditions of Mangroves in the Caribbean Marine Biodiversity Program Seascapes

The program, funded by USAID, seeks to achieve sustained biodiversity conservation, maintain ecosystem services, and improve human well-being for communities adjacent to marine protected areas (MPAs/MMAs). An important component of the program is evaluating the status of mangroves and monitoring changes in the system over time. The CMBP targeted mangrove sites include Parque Nacional Manglares Del Bajo Yuna in the Dominican Republic, Tyrrel Bay in Carriacou, Grenada, Caracol and Fort Liberte in Three Bays National Park, Haiti, and Ashton Lagoon in Union Island and St. Vincent and the Grenadines. These sites were selected based on their ecological importance and the need for conservation efforts. The total mangrove extent measured in these sites varied, with Parque Nacional Manglares Del Bajo Yuna having the largest area of 3,456 ha, followed by Three Bays National Park with 4,257.42 ha. Field surveys were conducted in 2016 and 2017 to document current and changing mangrove conditions. The surveys collected data on mangrove species composition, canopy height, diameter at breast height, and species richness and percent cover. Remote sensing was also used to identify and monitor changes in mangrove extent. Satellite imagery with a spatial resolution of 2x2m was used to detect changes in mangrove forests, while drone imagery was collected for smaller mangrove sites in Grenada and St. Vincent and the Grenadines. Satellite image classification was performed using an object-oriented image analysis approach, which contrasts with traditional pixel-based unsupervised classifiers. This approach allowed for the inclusion of non-spectral attributes of the imagery, such as texture, spatial, and contextual information, to improve accuracy. The software used for mapping was eCognition (v. 9.1, Trimble Inc.), which segmented the image into landscape objects that represented distinct patches of uniform mangrove habitat. Change detection of the mean Normalized Vegetation Difference Index (NDVI) value was calculated for each mangrove image segment using the Quickbird and WorldView-2 imagery. NDVI is a normalized ratio of red and NIR spectral reflectance, which is sensitive to leaf chlorophyll density and green leaf area. The NDVI model indicates areas of higher biomass in orange and red shades and lower biomass in blue and yellow shades. The results of the change detection analysis indicate increases, decreases, or no significant changes in mangrove systems at the target CMBP sites. The Parque Nacional Manglares Del Bajo Yuna showed a significant increase in mangrove extent, from 3,456 ha in 2013 to 3,654 ha in 2017. In contrast, the mangrove extent in Tyrrel Bay, Carriacou, Grenada, decreased from 26.48 ha in 2014 to 24.51 ha in 2017. The mangrove extent in Three Bays National Park, Haiti, remained relatively stable, with a slight increase from 4,257.42 ha in 2014 to 4,311.19 ha in 2017. The mangrove extent in Ashton Lagoon, Union Island and St. Vincent and the Grenadines, also remained relatively stable, with a slight decrease from 19.81 ha in 2015 to 19.45 ha in 2017. The results of the change detection analysis indicate that the mangrove systems in the CMBP targeted sites are dynamic and subject to changes due to natural and human-induced factors. The analysis provides valuable information for mangrove conservation and management efforts, and highlights the need for continued monitoring and research to understand the complex dynamics of mangrove ecosystems.