Photoacoustic device tracks ocean warming's impact on coral species

Many coral species, which are key for sustaining tourism, fishing, and human activity, may not survive beyond the end of this century due to ocean warming and acidification.

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Many coral species, which are key for sustaining tourism, fishing, and human activity, may not survive beyond the end of this century due to ocean warming and acidification. So properly evaluating the impact of these effects is crucial for more than 50 tropical countries and their coastal communities. Photoacoustics—the science of converting light-induced ultrasonic emissions to images—may just be the tool to provide key data, as it performs measurements quickly and doesn't require sample prep.

Professor Zvy Dubinsky, a researcher of aquatic photosynthesis at Bar-Ilan University (Ramat Gan, Israel), is leading the research to this end, alongside coral biologist Stefano Goffredo and chemist Giuseppe Falini of the University of Bologna in Italy. They, along with their research team, are addressing coral species evaluation through a five-year research project they're calling Corals and Global Warming: the Mediterranean Versus the Red Sea (CoralWarm). Funded by the European Research Council (ERC, Brussels, Belgium), CoralWarm combines field and laboratory experiments on Mediterranean and Red Sea coral species.

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The CoralWarm scientists had tried using various imaging techniques, including transmission electron microscopy (TEM), scanning electron microscopy (SEM), spectral imaging, and confocal laser microscopy, but found that none provide photosynthetic efficiency data. So they turned to time-consuming 14C labeling, oxygen evolution rates, and variable fluorescence to get it, explains Dubinsky.

Dubinsky started looking at photoacoustics as a tool for studying the optical properties and photosynthetic efficiencies of microalgal species while he was on sabbatical in the lab of Dr. David Mauzerall at Rockefeller University (New York, NY), he told BioOptics World. While there, he saw the potential of the method for determining photosynthetic light utilization efficiency of homogenous algal cultures, such as in coral.

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Using this work as a foundation, the research team developed a new photoacoustics-based tool that is handheld, submersible (SCUBA diver-operated), and enables rapid detection of the deterioration of coral reef communities. Dubbed ECHOGREEN and currently in proof-of-concept thanks to an ERC grant worth close to $200,000, the tool is non-destructive and therefore allows repeated measurements of the same samples, explains Dubinsky. What's more, each single measurement lasts 10 μs, allowing collection of 200–500 measurements in just a few minutes, he adds. The tool uses a 532 nm Q-switched Nd:YAG laser; as the researchers' main concern was the uneven surface of the coral and the inhomogenous distribution of the algae in the coral tissue, Dubinsky explains that expanding the laser pulse averaged the signal over a larger 0.5 cm diameter.

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ECHOGREEN could also be used to assess water quality in lakes, rivers, and reservoirs—important for those that are sources of drinking water. The tool already has a patent that covers the SCUBA diver-operated version and a business plan, says Dubinsky. Right now, they are working with a company on the design of a user-friendly prototype, as well as actively looking for potential partners to commercialize the tool in different photoacoustics-based configurations: the diver-operated version, a phytoplankton profiler, a benchtop laboratory instrument, and a flow-through version for optimizing algal mass culture operations.

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