Non-invasive estimation of coral polyp volume and surface area using optical coherence tomography

Abstract

The surface area (SA) and three-dimensional (3D) morphology of reef-building corals are central to their physiology. A challenge for the estimation of coral SA has been to meet the required spatial resolution as well as the capability to preserve the soft tissue in its native state during measurements. Optical Coherence Tomography (OCT) has been used to quantify the 3D microstructure of coral tissues and skeletons with nearly micron-scale resolution. Here, we develop a non-invasive method to quantify surface area and volume of single coral polyps. A coral fragment with several coral polyps as well as calibration targets of known areal extent are scanned with an OCT system. This produces a 3D matrix of optical backscatter that is analyzed with computer algorithms to detect refractive index mismatches between physical boundaries between the coral and the immersed water. The algorithms make use of a normalization of the depth dependent scatter intensity and signal attenuation as well as region filling to depict the interface between the coral soft tissue and the water. Feasibility of results is judged by inspection as well as by applying algorithms to hard spheres and fish eggs whose volume and SA can be estimated analytically. The method produces surface area estimates in calibrated targets that are consistent with analytic estimates within 93%. The appearance of the coral polyp surfaces is consistent with visual inspection that permits standard programs to visualize both point clouds and 3-D meshes. The method produces the 3-D definition of coral tissue and skeleton at a resolution close to 10 µm, enabling robust quantification of polyp volume to surface area ratios.

An unmanned aerial vehicle pipeline to estimate body volume at scale for ecological monitoring

“…In addition, methods exist for estimating the 3D surface area or volume of stationary aquatic species. For example, corals have been measured using handheld camera photogrammetry (Lange & Perry, 2020), satellite-based methods (Collin et al, 2021), optical coherence tomography (Jaffe et al, 2022), and underwater remotely operated vehicles (ROVs; Price et al, 2019).…”

“…In addition, methods exist for estimating the 3D surface area or volume of stationary aquatic species. For example, corals have been measured using handheld camera photogrammetry (Lange & Perry, 2020), satellite-based methods (Collin et al, 2021), optical coherence tomography (Jaffe et al, 2022), and underwater remotely operated vehicles (ROVs; Price et al, 2019). However, these methods are not easily adaptable to mobile species and so the challenge of developing a widely-applicable method for estimating the body volume of mobile species underwater remains unsolved.…”

Reconciling the variability in the biological response of marine invertebrates to climate change

“…Technological advancements, such as optical coherence tomography (Jaffe et al, 2022;Wangpraseurt et al, 2019), live confocal microscopy to measure tissue thickness (Huffmyer et al, 2020), tissue clearing coupled with light sheet fluorescence microscopy (Liu et al, 2020), chemical and hyperspectral imaging (Ricci et al, 2023), bioprinting of coral microhabitats (Wangpraseurt et al, 2022), mathematical modeling (Bouderlique et al, 2022;Murthy et al, 2023) and nanobiotechnology (Roger et al, 2023a,b), have already begun to further elucidate the internal environment of coral tissue with respect to oxygen levels, pH and light and the consequent biological responses to these environmental factors. These advances provide important avenues for continued research into how fine-scale differences in environmental parameters impact the biological responses of corals to various stressors.…”

Non-invasive investigation of the morphology and optical properties of the upside-down jellyfishCassiopeawith optical coherence tomography

“…In this context, optical coherence tomography (OCT) presents an attractive alternative imaging modality (Fercher et al, 2003; Huang et al, 1991; Schmitt, 1999), as it enables non-invasive in vivo imaging of live specimens using near infrared (NIR) wavelengths, allows for high-resolution tomographic scanning of tissue in real time, and enables 3D reconstruction of large samples with a potential depth of penetration of several millimeters depending on the scattering properties of the sample (Schmitt, 1999; Wangpraseurt et al, 2017b). Previous studies have utilized OCT for visualizing and quantifying structural characteristics, such as surface area, volume, and porosity in biofilms (Depetris et al, 2021; Wagner et al, 2010), terrestrial plants (Hettinger et al, 2000), and marine invertebrates (Speiser et al, 2016), including scleractinian corals (Jaffe et al, 2022; Wangpraseurt et al, 2017b; Wangpraseurt et al, 2019).…”