Optical spectra and pigmentation of Caribbean reef corals and macroalgae

Coastal reef degradation and widespread bleaching of corals, i.e. loss of p igments and/or symbiotic zooxanthellae, is increasing globally. Remote sens ing from boats, aircraft or satellites has great potential for assessing th e extent of reef change, but will require ground-verified spectral algorith ms characteristic of healthy and degraded reef populations. We collected se ven species of Caribbean reef corals and also representative macroalgae fro m reefs near Lee Stocking Island, Bahamas and quantified their pigments usi ng high performance liquid chromatography. We also measured the fluorescenc e and reflectance spectra of corals and macroalgae using an in situ benthic spectrofluorometer. In visibly pigmented (unbleached) coral from 4 to 5 m depth, the mean (+/- SD) surface density of pigments (3.0 +/- 1.3 mu g chlo rophyll-a cm(-2) and 2.1 +/- 0.7 mu g peridinin cm(-2)) was similar between colonies of the same species, but differed among species. The mean quantit y of pigment per zooxanthella(1.8 +/- 0.9 pg chi-a cell(-1) and 1.4 +/- 0.7 pg peridinin cell(-1)) also differed among species and sometimes between c olonies of the same species. Chi-a and peridinin densities per surface area of coral were positively correlated. When excited with blue light (480 nm) , macroalgae and corals had typical chlorophyll fluorescence with a peak at 680 nm and a smaller shoulder peak at 730 to 740 nm. Most corals, unlike m acroalgae, also had distinct fluorescence peaks between 500 and 530 nm. In visibly bleached corals 680 nm fluorescence was greatly reduced in amplitud e. Pigmented coral, under natural lighting conditions, had a reflected ligh t peak at about 570 nm. Reflectance increased over all wavelengths in bleac hed corals, with the greatest increase at the wavelengths where chlorophyll and accessory pigments absorb light, i.e. 670 and 450 to 550 nm. Both fluo rescence and reflectance spectra appear promising to remotely differentiate between pigmented and bleached coral and between coral and macroalgae.