Spectral reflectance of the seagrasses: Thalassia testudinum, Halodule wrightii, Syringodium filiforme and five marine algae

Spectral reflectance of three Western Atlantic subtropical/tropical dominant benthic seagrasses (Thalassia testudinum, Halodule wrightii and Syringodium filiforme) measured in the laboratory by UNIspec Spectral Analysis system over 400-1000 nm are compared to five Western Atlantic dominant benthic and intertidal algae (Fucus vesiculosus, Ulva lactuca, Halimeda incrassata, Udotea flabellum and Penicillus capitatus). Thalassia spectra are also compared to previously studied forest species, showing that the spectral reflectance signature of Thalassia was of the same general shape as forest species, but of lesser peak height (18% vs 28-50%) in the 750-759 nm range. For marine plants, near-infrared reflectance of Thalassia, Syringodium and Halodule was intermediate (18%) between the ubiquitous green alga Ulva (15%) and the temperate brown alga, Fucus (27%). The brown alga had a unique spectral signature in the first difference spectrum (three secondary peaks at differing spectral values than the other species' secondary peaks). Comparisons between Halodule, Syringodium and Thalassia near-infrared peaks and Halimeda (58%), Penicillus (29%) and Udotea (42%), subtropical/ tropical algae, were also carried out. Halimeda differed most from the other green algae in terms of numerous oscillations from 450 to 700 nm seen in the first difference spectrum. The three seagrasses were similar in spectral reflectance curve shape to one another but differed somewhat in peak height. The first difference spectrum was helpful in pointing out subtle differences among the species and between algae and seagrass. Spectral reflectance data such as those presented here appear potentially useful for remote sensing of shallow habitats, and may additionally be used to monitor their health.