Field Spectroscopy And Spectral Analysis Of Caribbean Scleractinian Reef Corals And Related Benthic Biota
Abstract
Coral reefs are highly heterogenic ecosystems with a plethora of photosynthetic organisms forming most of the benthic communities. Usually coral reef benthos is a composite of reef corals, different groups of algae, seagrasses, sandy bottoms, dead rubble, and even mangrove forests living in a relatively small area. The remote characterization of these important tropical ecosystems represents a challenge to scientists, particularly due to the similarity of the spectral signatures among some of these components. As such, we examined the similarities and differences between nine Scleractinian Caribbean shallow-water reef corals' spectral reflectance curves. Samples were also collected from each species for pigment analysis using High Performance Liquid Chromatography (HPLC). Reflectance curves were obtained with the aid of a GER-1500 hand-held field spectroradiometer enclosed in an underwater housing. Our findings showed that even though most of the pigmentation was directly related to the relationship of corals with their symbiotic dinoflagellates (zooxanthellae), the presence of other endolithic photosynthetic organisms can also contribute to the light absorption of corals and, hence, the reflectance spectra of each species. Also, the relative contribution of chlorophylls vs. carotenes or xanthophylls depends on the coral species with some species relying more on Chlorophyll a and other species relying on Chlorophyl c2 and Peridinin with a small Chlorophyll a component. Pigments associated with the xanthophyll cycle of dinoflagellates (Diadinoxanthin and Diatoxanthin) were detected in most species. Pigments typical of endolithic organisms such as Zeaxanthin, Fucoxanthin, Violaxanthin and Siphonaxanthin were also detected in some coral species. The influence of major pigments on the reflectance curve was evidenced with a 2nd derivative analysis. This could be used to discriminate among most species. Further, an analysis of the integration of the area under the reflectance curve in the photosynthetically active radiation (PAR; 400-700nm) yielded an inverse relationship with the total pigment concentration with an up to 97% confidence level. Corals were distinguished from seagrasses and other benthic components based on their reflectance and differences in curve inflection peaks. Special care needs to be taken when characterizing sandy bottoms as they are influenced by the presence of photosynthetic microbiota as reflected in their reflectance curves. The use of this integration is proposed as a novel non-invasive method to predict pigment changes in reef corals aimed to monitor their health in the present climate change scenario.
- Publication:
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AGU Spring Meeting Abstracts
- Pub Date:
- May 2013
- Bibcode:
- 2013AGUSMOS21A..02T
- Keywords:
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- 4220 OCEANOGRAPHY: GENERAL / Coral reef systems;
- 1640 GLOBAL CHANGE / Remote sensing;
- 4872 OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL / Symbiosis