Field spectrometry: New methods to investigate epilithic micro-algae on rocky shores

The use of field reflectance spectrometry to detect and quantify chlorophyll-a in intertidal epilithic micro-algae is evaluated. Sandstone disks were placed into intertidal areas for different amounts of time to accumulate micro-algae. Field reflectance spectra (350-1050 nm) were acquired from each of the disks before and after they were collected from the intertidal zone. Pigments were extracted from the sandstone disks using methanol and chlorophyll-a concentration was determined spectrophotometrically. Other pigments were identified using High Performance Liquid Chromatography (HPLC). Different ratios of reflectance were tested. A ratio of reflectances at 750 and 670 nm (R-750/R-670) had the tightest correlation with chlorophyll-a (R-2 = 0.93; SE= 1.14; P= < 0.001; n = 25). Data from the field were used to predict values of chlorophyll-a, predictions were strongly and linearly related to observed values (R-2 =0.95; SE = 0.15; P < 0.001; n=8). The average difference and average absolute difference between observed and predicted values of chlorophyll-a was 0.03 mu g cm(-2) (1.79% of the measured range) and 0.14 mu g cm(-2) (8.38% of the measured range), respectively. Absorptions due to chlorophylls a, b and c, carotenoids and the phycobiliproteins phycoerythrin, phycocyanin and allophycocyanin were identified. The techniques described here enable estimation of amounts of chlorophyll-a and the detection of several other pigments. Thus, investigations of microflora in studies of succession, biofilms or grazing in intertidal habitats can be enhanced by field spectrometry. (c) 2005 Elsevier B.V. All rights reserved.