Using Scuba for In Situ Determination of Chlorophyll Distributions in Corals by Underwater Near Infrared Fluorescence Imaging

Abstract

Studies reporting quantitation and imaging of chlorophyll in corals using visible fluorescent emission in the red near 680 nm can suffer from competing emission from other red-emitting pigments. Here, we report a novel method of selectively imaging chlorophyll distributions in coral in situ using only the near infrared (NIR) fluorescence emission from chlorophyll. Commercially available equipment was assembled that allowed the sequential imaging of visible, visible-fluorescent, and NIR-fluorescent pigments on the same corals. The relative distributions of chlorophyll and fluorescent proteins (GFPs) were examined in numerous corals in the Caribbean Sea, the Egyptian Red Sea, the Indonesian Dampier Strait, and the Florida Keys. Below 2 m depth, solar induced NIR chlorophyll fluorescence can be imaged in daylight without external lighting, thus, it is much easier to do than visible fluorescence imaging done at night. The distributions of chlorophyll and GFPs are unique in every species examined, and while there are some tissues where both fluorophores are co-resident, often tissues are selectively enriched in only one of these fluorescent pigments. Although laboratory studies have clearly shown that GFPs can be photo-protective, their inability to prevent large scale bleaching events in situ may be due to their limited tissue distribution.

Experimental Techniques to Assess Coral Physiology in situ Under Global and Local Stressors: Current Approaches and Novel Insights

“…A fundamental measure of coral status is quantification of the light-harvesting pigments of the endosymbionts over time, whereby decreasing trends may provide early warning of the onset of bleaching events. The underwater fluorescence imaging has been adapted to conduct large-scale in situ assessments of coral reefs, through the detection of chlorophyll and green fluorescent proteins wide spatial scales ( Treibitz et al, 2015 ; Oh et al, 2020 ). Chlorophyll concentrations are indicative of photo-acclimation, among other things, and green fluorescent proteins may, in addition to being a signal of tissue repair ( D’Angelo et al, 2012 ), contribute to photoprotection in corals; and thus, quantifying these concentrations can provide crucial information on the bleaching susceptibility or resistance of corals ( Salih et al, 2000 ; Kenkel et al, 2011 ; Roth and Deheyn, 2013 ).…”

Experimental Techniques to Assess Coral Physiology In Situ: Current Approaches and Novel Insights

“…A fundamental measure of coral status is quantification of the light harvesting pigments of the endosymbionts over time, whereby decreasing trends can provide early warning of the onset of bleaching events. The underwater fluorescence imaging has been adapted to conduct large-scale in situ assessments of coral reefs, through the detection of green fluorescent proteins in corals [85,86]. Because the concentration of these pigments and fluorescent proteins are directly involved in photoprotection and photo-acclimation, quantifying the concentrations present in a coral population or community can provide crucial information on bleaching susceptibility or resistance [87][88][89].…”

Experimental Techniques to Assess Coral Physiology In Situ: Current Approaches and Novel Insights

“…Underwater fluorometryThe photochemical performance of coral endosymbionts is a key aspect influencing the health of scleractinian corals, so measures of holobiont photophysiology provide insight to coral metabolic status.Fluorometry can provide insight in two broad ways: a measure of the abundance, character, and distribution of light-harvesting pigments and fluorescent proteins in corals (i.e., the potential energy source), and the photophysiological status of the endosymbiont i.e., how well these pigments are being used to generate energy for the coral.A fundamental measure of coral status is quantification of the light harvesting pigments of the endosymbionts over time, whereby decreasing trends can provide early warning of the onset of bleaching events. The underwater fluorescence imaging has been adapted to conduct large-scale in situ assessments of coral reefs, through the detection of green fluorescent proteins in corals[91,92]. Because the concentration of these pigments and fluorescent proteins are directly involved in photoprotection and photo-acclimation,…”