Digital image processing to detect subtle motion in stony coral

Abstract

Coral reef ecosystems support significant biological activities and harbor huge diversity, but they are facing a severe crisis driven by anthropogenic activities and climate change. An important behavioral trait of the coral holobiont is coral motion, which may play an essential role in feeding, competition, reproduction, and thus survival and fitness. Therefore, characterizing coral behavior through motion analysis will aid our understanding of basic biological and physical coral functions. However, tissue motion in the stony scleractinian corals that contribute most to coral reef construction are subtle and may be imperceptible to both the human eye and commonly used imaging techniques. Here we propose and apply a systematic approach to quantify and visualize subtle coral motion across a series of light and dark cycles in the scleractinian coral Montipora capricornis. We use digital image correlation and optical flow techniques to quantify and characterize minute coral motions under different light conditions. In addition, as a visualization tool, motion magnification algorithm magnifies coral motions in different frequencies, which explicitly displays the distinctive dynamic modes of coral movement. Specifically, our assessment of displacement, strain, optical flow, and mode shape quantify coral motion under different light conditions, and they all show that M. capricornis exhibits more active motions at night compared to day. Our approach provides an unprecedented insight into micro-scale coral movement and behavior through macro-scale digital imaging, thus offering a useful empirical toolset for the coral research community.

High-frequency imagery to capture coral tissue (Montipora capricornis) response to environmental stress, a pilot study

“…The basic aquarium setup was similar to the setup in this reference [ 21 ]. A colony of Montipora capricornis (around 15 mm × 20 mm) bought from a local store was raised in a 11.36 L aquarium (37.1 cm × 22.4 cm × 28.4 cm) with specific gravity of artificial seawater = 1.024 and pH = 8.4 [ 21 ]. Artificial seawater was made from Instant Ocean Reef Crystals Reef Salt.…”

“…To fully capture the dynamics of a system, the sampling frequency needs to be properly selected. Since the frequency of coral tissue motions of Montipora capricornis was identified to range from 0 min -1 to 0.25 min -1 , we chose to capture images of the coral every two minutes in our experiment [ 21 ]. For experimental studies, inconsistencies in lighting conditions in the underwater environment and depth can cause heavy color distortions of the captured images, which poses challenges related to color analysis and identification.…”

“…with a certain level of randomness or uncertainty) at different levels, from organs function (brain signals) to individual organism itself [ 22 , 23 ]. Corals also display stochastic behaviors in relation to tissue motion and polyp motion [ 21 , 23 ]. The corresponding temporal dynamics can be characterized by several measures, such as spatial distance and correlation.…”

Cellular adaptations leading to coral fragment attachment on artificial substrates in Acropora millepora (Am-CAM)

“…Live and static imaging is an effective way to detail the structures of reef-building corals at the organismal, tissue and cellular levels 6 , 38 , 40 – 45 . Recent advancements in imaging techniques have provided vital insight into coral calcification, biomechanics and cellular plasticity 38 , 40 – 43 , including non-invasive techniques for dynamic temporal imaging at high resolution, such as in vivo video and time-lapse microscopy 46 – 48 and novel static imaging 41 – 43 . The use of in vivo observations is maximised when used in combination with static microscopy to increase the resolution of observation in characterising soft tissue and skeletal development 6 , 43 , 49 .…”

Revealing the Systematic Nature of Coral Attachment to Reef Substrates

“…Recent advancements in imaging have provided vital insights into coral calci cation, biomechanics, and cellular plasticity 30,36,38−40 . These works highlight the ongoing importance of developing noninvasive techniques for dynamic imaging at high temporal resolutions, such as in vivo video and time-lapse microscopy and novel static methods 36,39,40 . The utility of the in vivo observation is maximised when used in combination with novel sample preparations for cellular and mineralized composites (skeleton) to maximise the observable capacity for static microscopy, including images produced by electron microscopy.…”