Anthropogenic noise pollution is dramatically altering the home of millions of marine species. Commercial shipping, seismic exploration and drilling for oil and gas, and the use of sonar for military purposes are making the oceans an increasingly noisy place. Ocean acidification is putting a megaphone to such practices by decreasing the concentrations of sound-absorbing chemicals such as borate and carbonate1. The current trend of increasing anthropogenic carbon emissions and noise pollution is unsustainable. We have to change our behavior before our impact on marine biodiversity becomes irreversible.
While the focus of media attention regarding anthropogenic noise pollution has been on marine mammals, hearing can be an equally important sense for fish as well. Sound travels faster in water than air, and perhaps as a result, many types of marine organisms have developed hearing as a primary sense for navigating through the murky depths. Recent studies have shown that fish grown in water with high levels of CO2 lost their ability to avoid reef noise2. This represents a severe impairment of natural sensory responses necessary for predatory avoidance, reproduction, feeding, habitat selection, navigation, and communication.
The inner ear structures of many fish are composed of aragonite, and are thus susceptible to decalcification as a result of ocean acidification3. Although the impact of this phenomenon on fish hearing is not fully understood, it demonstrates that the consequences of anthropogenic carbon emissions are far reaching. It may never be possible to assess the total impact our lifestyle is having on our environment.
Fishing is a 60 billion dollar industry. Over 100 million tons of fish are consumed each year, providing 2 billion people worldwide with at least a fifth of their average animal protein intake4. Aggressively polluting the environment of organisms so crucial to the survival of our own species is masochistic. How can we justify exploiting the oceans to satisfy current demand if it means sentencing future generations to a world with scarcer food sources?
Several things could be done to improve sustainability. The increase in commercial shipping over the last few decades itself has contributed to a 12 dB increase in ambient ocean noise5. Diverting shipping lanes away from organism-rich ocean zones would help limit the impact of noise pollution on marine animals if curbing the amount of shipping itself is not possible. Marine protected areas have been successfully instituted to shelter cetaceans from anthropogenic noise polluters6. Such guidelines require strict enforcement and must be expanded to protect fish and invertebrate species. Seismic exploration of the ocean floor involves the use of airguns, or underwater cannons that eject compressed air every ten seconds. Such sounds can propagate far beyond the source, causing tissue damage and deafness in thousands of organisms7. Countries need to develop ways to conduct such surveys that minimize such environmental casualties. Ocean acidification will continue to intensify the ill effects of anthropogenic noise pollution by decreasing seawater sound absorption and decalcifying fish ear structures unless something is done to reduce carbon emissions.
It is widely accepted by the community of ocean scientists that ocean acidification seems to have little effects on adult fish. A study conducted by Philip L. Munday, of the James Cook University, set out to test the effects of increased CO2 levels in water on young fish. Because adult fish can regulate their acid-base levels via their gills, they can adjust to acidity changes that occur in the waters around them. But the young ones haven’t yet developed that mechanism, so the hypothesis was that more acidic waters would have an effect on them, and more particularly on their otolith (ear bones) development which are made of aragonite. Batches of Damselfish hatchlings were placed in 4 separate aquariums with different CO2 for three weeks after which they were killed and their growth was measured. The results showed that there were no significant differences in skeletal size and otolith size and shape among the four batches of fish. This therefore led to the conclusion that young fish, particularly young Damselfish have some resistance water acidity changes.
Source: Marine Ecology Progress Series, Vol. 423: 211-211, 2011