Wide Field-of-View Fluorescence Imaging of Coral Reefs

Abstract

Coral reefs globally are declining rapidly because of both local and global stressors. Improved monitoring tools are urgently needed to understand the changes that are occurring at appropriate temporal and spatial scales. Coral fluorescence imaging tools have the potential to improve both ecological and physiological assessments. Although fluorescence imaging is regularly used for laboratory studies of corals, it has not yet been used for large-scale in situ assessments. Current obstacles to effective underwater fluorescence surveying include limited field-of-view due to low camera sensitivity, the need for nighttime deployment because of ambient light contamination, and the need for custom multispectral narrow band imaging systems to separate the signal into meaningful fluorescence bands. Here we describe the Fluorescence Imaging System (FluorIS), based on a consumer camera modified for greatly increased sensitivity to chlorophyll-a fluorescence, and we show high spectral correlation between acquired images and in situ spectrometer measurements. This system greatly facilitates underwater wide field-of-view fluorophore surveying during both night and day, and potentially enables improvements in semi-automated segmentation of live corals in coral reef photographs and juvenile coral surveys.

Scaling up Ecological Measurements of Coral Reefs Using Semi-Automated Field Image Collection and Analysis

“…The first involves recent development in the field of automated image analysis using deep Convolutional Neural Networks (CNNs) which have dramatically increased the classification accuracy for a wide range of images [89,90]. The second involves the opportunity to complement the RGB camera used here with multi-spectral or fluorescence cameras [91]. In this case, collecting additional spectral information could improve the ability to detect additional spectral signals, thereby improving precision and accuracy when distinguishing visually overlapping categories.…”

In situ Analysis of Coral Recruits Using Fluorescence Imaging

“…Even though the camera was placed on a frame positioned on the seabed, there were still small movements that caused slight differences between the images. In Treibitz et al (2015) the images were aligned manually. In the present case, to overcome these movements and register the image pairs automatically, we developed an image registration algorithm written in MATLAB (Mathworks, Inc.; Akkaynak, 2017).…”

“…Consequently, most studies detecting fluorescence in situ take place at night to avoid ambient light illumination (Piniak et al, 2005;Baird et al, 2006). Treibitz et al (2015) showed that fluorescence could be imaged during daytime by subtracting the ambient light image (captured with the strobes off).…”

Development of a Regional Coral Observation Method by a Fluorescence Imaging LIDAR Installed in a Towable Buoy

“…In satellite remote sensing, coral observation is disturbed by waves on the sea surface and the absorption and scattering of light in seawater [5]. Underwater investigations are hindered by the narrow field of view (hereafter FOV) and slow survey speed [6]. The present study attempts to improve coral observation with a boat-based observation technique.…”

“…Because these damages diminish the coral cover within a short time, reliable and frequent coral viability checking is essential for coral monitoring. To assess coral viability, we can exploit the fluorescence properties of corals [6]. The surface tissue of most corals contains innate fluorescent proteins, which emit at blue-to-green wavelengths (400-570 nm) under ultraviolet (hereafter UV) excitation [8].…”