Use of hyperspectral reflectance to non-destructively estimate seagrass Zostera noltei biomass

Abstract

Seagrasses are marine plants ranked worldwide amongst the most valuable coastal ecosystems. The global conservation effort requires accurate estimation of seagrass abundance and taxonomic composition. Hyperspectral reflectance has been used to estimate seagrass biomass, despite requiring destructive laboratory measurements that goes against conservation principles.Therefore, we assessed the efficiency of Zostera noltei hyperspectral reflectance to estimate its aboveground biomass in intertidal areas, having Ria de Aveiro coastal lagoon (Portugal) as a case study, with seasonal samplings during a whole year comparing (non-destructive) field- and (destructive) laboratory-based measurements of the spectral signature. Several vegetation indices (VIs) that focus on the spectral absorption of specific pigments were also tested: Normalized Difference Vegetation Indices (NDVI)-like ratios, Double Difference (DD)-like Ratios and Simple Ratios (SR).Here we show that Z. noltei hyperspectral signature, measured in the field and in the laboratory, is clearly related to the aboveground biomass of the plant along the year. We found that among the VIs, NDVI-like ratios showed higher correlation with Z. noltei aboveground biomass than the other types of VIs. Taking into consideration the sensitivity to biomass saturation, the NDVI705 was identified as the best vegetation index to estimate Z. noltei biomass during the whole year and in both type of measurements, up to a saturation level, also demonstrating the successful use of non-destructive methods.The suitability of hyperspectral reflectance measurements in order to estimate Z. noltei aboveground biomass was confirmed, confirming also the potential efficient use of field-based measurements (non-destructive) for conservation practices and sustainable management of the species in intertidal ecosystems and allowing aboveground biomass to be potentially proposed as a metric for the evaluation of seagrass healthy condition under EU policies (e.g. Water Framework Directive, Marine Strategy Framework Directive).