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Ocean acidification can make some species shine brighter

A more acidic ocean could give some species shine.

As the pH of the ocean decreases as a result of climate change, some bioluminescent organisms may become brighter, while others see their dark lights, scientists report on Jan. 2 at the Society for Integrative and Comparative Biology's annual virtual meeting.

Bioluminescence is strictly in parts of the ocean (SN: 19/05/20). The ability to illuminate darkness has evolved more than 90 times in different species. As a result, the chemical structures that create bioluminescence vary enormously, from individual chains of atoms to massive ringed complexes.

With such variability, changes in pH could have unpredictable effects on creatures ’ability to glow (SN: 7/6/10). If fossil fuel emissions continue as they are, the average pH of the oceans is expected to drop from 8.1 to 7.7 by 2100. To find out how bioluminescence may be affected by that decline, sensory biologist Tom Iwanicki and colleagues from the University of Hawaii at Manoa brought together 49 studies on bioluminescence in nine different strands. The team then analyzed data from those studies to see how the brightness of the creatures ’bioluminescent compounds varied at pH levels from 8.1 to 7.7.

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As the pH drops, bioluminescent chemicals in some species, such as marine thought (Renilla reniformis), double in light production, the data showed. Other compounds, such as those of the sea firefly (Vargula hilgendorfii), show modest increases of only 20 percent. And some species, such as zucchini (Watasenia scintillans), appear to have a 70 percent decrease in light production.

For the sea firefly, which uses bright trails to attract mates, a small hike could give it a sexy edge. But for firefly squid, which also uses luminescence for communication, low pH and less light may not be a good thing.

Because the work was an analysis of previously published research, “I’m interpreting this as a first step, not as a definitive result,” says Karen Chan, a marine biologist at Swarthmore College Pennsylvania who did not participate in the study. "It provides (a) verifiable hypothesis that we must … analyze."

Iwanicki agrees that the next step is to definitely try. Most of the studies analyzed removed luminescent chemicals from an organism to test them. It will be crucial to find out how compounds work in ocean creatures. “Across our oceans, 75 percent of visible critters are capable of bioluminescence,” says Iwanicki. "When we're older changing the conditions under which they can use that (ability) … that will have a world of impacts."

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