08 Jul 2025
BUMP platform gives color and fluorescence data from underwater observations.
An imaging platform developed at the Scripps Institution of Oceanography (SIO) could help reveal new details of coral microstructure and health.
Described in Methods in Ecology and Evolution, the instrument is designed to offer an unprecedented look at coral photosynthesis on the micro-scale.
The device is a development of earlier work on the use of pulse amplitude modulated (PAM) light measurements, in which the photochemistry of chlorophyll-containing systems can be studied by quantifying the fluorescence of chlorophyll at different redox states and under different light stimulation.
This technique is more straightforward on dry land than under the sea, but the advantages to researchers of successfully observing aquatic photosynthesis in situ are considerable.
So SIO set out to design an enhanced PAM platform, one enabling visual observations and variable chlorophyll fluorescence imaging in an underwater environment. Developed by SIO’s Jaffe Lab for Underwater Imaging, the instrument is christened the Benthic Underwater Microscope imaging PAM, or BUMP.
“This microscope is a huge technological leap in the field of coral health assessment,” said Or Ben-Zvi, postdoctoral researcher at Scripps Oceanography and lead author of the study.
“Coral reefs are rapidly declining, losing their photosynthetic symbiotic algae in the process known as coral bleaching. We now have a tool that allows us to examine these microalgae within the coral tissue, non-invasively and in their natural environment.”
Ocean photosynthesis: important for life on Earth
BUMP’s microscope unit includes as its light source an array of LEDs with a pair of Fresnel lenses, condensing the illumination onto an area of 1 cm2 for blue illumination or 4 cm2 for white illumination. Short exposures down to 50 microseconds are used to minimize motion blur and reduce the illumination’s effect on natural photosynthesis.
“With the PAM technique, the red fluorescence is measured to provide an index of how efficiently the microalgae are using light to produce sugars,” commented SIO. “The cyan/green fluorescence, concentrated around specific areas such as the mouth and tentacles of the coral, is attributed to special fluorescent proteins produced by the corals themselves that play multiple roles in the coral’s life functions.”
Trials of BUMP have included deployment at 12 meters depth under ambient light conditions in Maui, Hawaii, where the instrument revealed how the corals actively changed their volume and shape constantly. The project was able to add new observations to previously documented coral behavior, such as seeing a coral polyp trying to capture or remove a passing particle by rapidly contracting its tentacles.
Data collected with the new microscope could help reveal early warning signs appearing before corals experience irreversible damage from global climate change events, such as marine heat waves. These insights could help guide mitigation strategies to better protect corals.
Beyond corals, the tool has widespread potential for studying other small-scale marine organisms that photosynthesize, such as baby kelp. Researchers at Scripps Oceanography are already using the BUMP imaging system to study the early life stages of the elusive giant kelp off California.
“Since photosynthesis in the ocean is important for life on Earth, a host of other applications are imaginable with this tool, including right here off the coast of San Diego,” said the project.