The natural pH of seawater is 8.2. The addition of carbon dioxide emissions into the world oceans, of which they have absorbed approximately half, has dropped the pH to 8.1. By the end of the century, the pH of the world’s oceans may drop to only 7.8. The increasing acidic environment has put the oceans’ marine life in jeopardy, from coral to fish.
A recent study performed in Papua New Guinea in a naturally carbon dioxide rich environment found that by the end of the century coral may be severely limited to nonexistent due to the pH levels. Coral provide a home for a plethora of species, from aquatic plants to hundreds of fish species. The loss of coral would spell disaster for many species which would likely disappear along with the coral.
Another study, which was conducted in a laboratory with clownfish, found that increasing ocean acidity may have additional consequences on fish hearing as well-consequences which would occur before coral disappeared. In the study, which was published in the journal Biology Letters, scientists raised clownfish in waters of differing acidities. One set of clownfish were raised in waters as they are today, with 390 parts per million of carbon dioxide. Other clownfish were raised at 600, 700 and 900 parts per million to reflect potential levels later in the century.
The scientists set up a test chamber in which they would emit predator noises from a loudspeaker. The scientists found that the clownfish raised in the waters with today’s level of carbon dioxide, 390 parts per million, largely avoided the end emitting the predator noises. Seventy-five percent of the clownfish remained at the end of the tank away from the noises during the tests. It is unknown whether a larger percentage would have avoided the predatory noises prior to the industrial age emissions.
However, in waters with high acidities, the clownfish seemed unaffected by the predatory noise. The scientists determined that the higher acidities caused the clownfish to become deaf. The scientists did not determine any physical problems with their ears, leading them to believe that it was likely due to an issue with their nerves due to the acidity levels.
Obviously avoiding predators for any species is a key to survival, so the loss of hearing for the clownfish would be severely debilitating for the species. In addition to needing hearing ability to avoid predators, the fish also rely on it for many of their life functions. Steve Simpson, from the United Kingdom’s Bristol University, stated: “Sounds are also important for mate detection, pack hunting, foraging-so if any or all of those capacities are gone, you’d have a very lost fish.”
The scientists do not know whether the clownfish could adapt over time to increasingly acidic waters if the growing acidity spanned decades. However, if acidity occurs in a shorter time frame adaptation is unlikely to occur. Whether or not other species would become hearing impaired due to rising acidities is not yet known.