Assessing the significance of leaf chlorophyll content for measuring the vegetation health in mangrove species along the Kerala Coast, India – A multi-proxy approach

This study aimed to estimate the chlorophyll content of mangrove species distributed along the Kerala coast of India, and also to address the critical issue of assessing the health of these ecosystems. We identified 16 mangrove species and estimated their chlorophyll concentration levels through a combination of field reconnaissance, in situ radiometric measurements at 218 locations, and UV spectrophotometric (ultraviolet–visible) analysis in the laboratory, and estimated the vegetation health from spectral indices using IRS (Indian Remote Sensing) Resourcesat LISS-IV (Linear Imaging and Self-Scanning Sensor) satellite imagery. This study revealed that the dominant species in Kerala are Avicennia officinalis, A. marina, Rhizophora mucronata and Excoecaria agallocha, whereas, Bruguiera sexangula is sparsely spread. Approximately 14 % of the mangrove cover along the Kerala coast is under stress due to various factors, including climate change and anthropogenic influences. Significantly, two of the 16 species, Avicennia marina and Rhizophora appiculata appeared relatively healthy, with average chlorophyll concentration index (CCI) values of 311.89±40.13 µmol/m2 and 553.42±23.24 µmol/m2, respectively. However, other dominant species Avicennia officinalis, Rhizophora mucronata, and Excoecaria agallocha exhibited average CCI values of 582.35±147.61, 611.7±104.58, and 559.04±141.13 respectively, and seemed to be under stress, calling for serious conservation measures. Our study also revealed the potential of cost-effective IRS LISS-IV imagery for identifying mangrove species and for estimating the chlorophyll concentration and plant vigour together with field and laboratory observations and measurements.