Assessment of Coral Reef Eutrophication Thresholds Across Puerto Rico Using In-situ and Satellite-derived Chlorophyll-a
摘要
Quantifying chlorophyll-a (Chl-a) is critical for assessing eutrophication in coral reef ecosystems to guide management and restoration efforts. However, eutrophication assessments are limited by the resource-intensive collection and analysis of Chl-a, while satellite estimates are complicated by bottom reflectance in shallow coastal areas. This study compared in situ Chl-a observations from Puerto Rico Coral Reef Monitoring Program sites with satellite-derived Chl-a estimates from Sentinel-3 OLCI sensor relative to published eutrophication thresholds. Satellite-derived Chl-a values (mean = 0.99 µg/L; range = 0.05 to 4.76 µg/L) overestimated in situ measurements (mean = 0.36 µg/L; range = 0.00 to 1.65 µg/L) by 0.60 ± 0.14 µg/L, with shallower sites exhibiting higher values. In situ measurements were used to guide the selection of nearby virtual stations, yielding satellite derived Chl-a values (mean = 0.38 µg/L; range = 0.07 to 0.72 µg/L) that were not detectably different from in-situ observations, although greater temporal variability was observed near river-influenced areas. Most sites exceeded the conservative 0.2 µg/L eutrophication threshold, with fluvially impacted sites exceeding the least conservative 0.5 µg/L threshold. This research highlights the limitations of current satellite algorithms in shallow, optically complex environments, where false-positive threshold exceedances may occur. We provide a practical approach for enhancing Chl-a monitoring at shallow coral reef virtual stations using in situ Chl-a data while more accurate Chl-a algorithms are developed. This study advances our understanding of the limitations and potential uses of satellite remote sensing in coral reef ecosystems, offering insights to optimize monitoring and better inform reef management.