Increase in ocean acidification could lead to lost fish larvae in quiet reefs

(Phys.org)—A small team of researchers has found evidence that suggests that as the oceans acidify due to increased carbon dioxide levels, some fish larvae may become lost while looking for a home. In their paper published in the journal Biology Letters, Tullio Rossi, Ivan Nagelkerken, Jennifer Pistevos and Sean Connell, all with The University of Adelaide describe their study of a natural environment that mimics oceans of the future and their experiments with larvae exposed to increased acidification levels

Many studies have been done with the goal of better understanding what will happen in the ocean as acidification occurs, but few if any have looked into the possible impact due to changes in sound dispersal. Prior research has shown that fish larval dispersion and then the subsequent finding of a home, is tied very closely to sound—marine life living on a coral reef makes a lot of noise and can serve as a beacon. Fish larvae have evolved an ability to use the noise to find their way home after riding currents for days, weeks or months. But, the researchers wondered, what will happen if the reefs become quieter due to the existence of less marine life in a more acidic ocean?

To find out, they ventured first to an undersea carbon dioxide vent off the coast of New Zealand where acidification levels are close to what many believe will become the norm over the next hundred years—they sank microphones and recorded underwater sounds and found that there was much less natural noise than in nearby areas where acidification levels were normal. That suggested that an increase in acidification would indeed mean a quieter underwater world.

Next, the researchers went back to their lab and tested mulloway fish larvae responding to changes in acidification—first they exposed a test group to high levels of carbon dioxide for nearly a month, then they put them in a tank to see if they would make their way using acoustic cues, to what should be their natural environment. They did not, they instead avoided them—larvae reared in a normal environment responded positively, as expected. The team also tried putting the damaged larvae in a tank where the conditions were similar to that around the natural carbon dioxide vent and found that they tried to avoid that environment as well. Their simple experiments indicate, the team suggests, that some fish larvae in the future might have to find another way home, or perish.

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