Changes in the fluorescence of the Caribbean coral Montastraea faveolata during heat‐induced bleaching

Abstract

In order to evaluate the response of commonly occurring green and orange fluorescent host-based pigments, a thermal stress experiment was performed on specimens of the Caribbean coral Montastraea faveolata. Seven paired samples were collected from a small oceanic reef near Lee Stocking Island in the Bahamas. Seven of the fourteen corals were subjected to elevated temperatures for 28 d, followed by a recovery period lasting 53 d. Throughout the experiment, high-resolution (ϳ400 m pixel Ϫ1 ) multispectral images of induced fluorescence were recorded at wavelengths corresponding to the green and orange host pigments, plus chlorophyll. These images revealed that the fluorescence of both host pigments was concentrated at polyp centers and declined by 70-90% in regions between polyps. Chlorophyll fluorescence, however, was distributed almost uniformly across the entire coral surface, but with decreases of 10-30% around polyp centers. A normalized difference ratio between the green and orange pigments (GO ratio) was developed to facilitate comparison with chlorophyll fluorescence as a bleaching indicator. Analysis showed a high correspondence between a sustained GO ratio of less than zero and the death of corals. Finally, this ratio was resistant to contamination from other sources of chlorophyll fluorescence, such as filamentous algae.

Automated annotation of coral reef survey images

“…First, we used fluorescence information to improve the classification accuracy of the dominant benthic classes by 2.7%, which is equivalent to a 22% relative reduction of error-rate. In contrast to previous work that investigated the use of fluorescence spectra to classify groups defined by their level of bleaching [93], fluorescence signatures [148,88], or other physiological states [118,149,36], our work provides evidence that the fluorescence signatures can be directly related to benthic taxonomy. Second, most work on coral fluorescence has relied on relatively expensive spectrometers or custom multi-spectral cameras which have high spectral but limited spatial resolution [148,88].…”

“…Multispectral cameras, underwater spectrometers, underwater radiometers and underwater fluorometers (diving PAMs) have been previously used to quantify physiological parameters of coral reef organisms [133]. Another option is to measure fluorescence signatures which have been shown to contain ecologically relevant information such as level of bleaching [93], recruitment levels [133], and physiological state [149]. However, until recently, fluorescence imaging systems were limited either by resolution [149], spatial coverage of the measurements [87,147] and/or ease of operation [87,149,88].…”

Effects of cold stress and heat stress on coral fluorescence in reef-building corals

“…In a heat stress experiment of Montastrea faveolata, the ratio of green to orange fluorescence switched when corals bleached and eventually died, then being mainly orange52. However, it was not determined if the source of the orange fluorescence was from coral FPs or phycoerythrin from endosymbiotic cyanobacteria53.…”

Peer Review #1 of "Effects of reduced dissolved oxygen concentrations on physiology and fluorescence of hermatypic corals and benthic algae (v0.1)"

“…Emission in red, at wavelengths longer than 630 nm, is not generated by the coral host (Mazel 1995, Salih et al 2000., Neori et al 1988), but from photosynthetic pigments found in their algal symbionts (Jeffrey and Haxo 1968), which show a distinct chlorophyll peak at 680 nm (red light) when excited with blue light (480 nm) (Gurskaya et al 2001). The detected rise in red fluorescence for corals in low oxygen treatments may therefore either be attributed to increases in zooxanthellae (yet unlikely since the corals were bleached and dying), or to the growth of endolithic algae (already present in the coral skeleton), cyanobacteria and/or filamentous algae starting to colonize the bare coral skeleton (Shashar et al 1997;Zawada and Jaffe 2003).…”