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October 25, 2012

Ocean Acidification: A Big Problem

It’s uncharted territory as atmospheric carbon dioxide acidifies our oceans.

Our oceans are under assault, but not from on the surface or under the surface. They are under assault from above. As the atmosphere becomes more saturated with carbon dioxide, this gas is absorbed by seawater. This absorption creates carbonic acid, essentially the same compound that creates the fizz in carbonated beverages. Even very small changes in the pH of ocean waters have a big impact on a wide variety of species, and measurable declines in pH have already been recorded by scientists monitoring the world’s oceans.

First, let me state emphatically that this is not a discussion about “climate change” or “global warming” or whatever one wants to call it. We know that our atmosphere is becoming more and more saturated with carbon dioxide, most likely from a combination of sources. Some of it may be from a natural warming cycle, and some of it is from the burning of fossil fuels, but it is there in ever-increasing levels.

Scientific estimates are that about one-third of all the carbon dioxide released into the atmosphere by burning fossil fuels is absorbed by the ocean. That amounts to a staggering 1 million tons every hour. Already the effects of ocean acidification are showing up in a number of species that are at the bottom of the trophic pyramid, or ocean food web. Perhaps estuarine areas, which normally are more confined, experience
a higher level of impact from the carbonic acid. They also have higher levels of carbonic acid, but we’ll get to that later. In some areas, ocean acidification has caused the complete destruction of soft-shell clams by dissolving the shells of the juveniles.

The higher acidity has the ability to impact all shellfish. Along with increased water temperature, it has been shown to impact living corals, which essentially give reef structures their high level of productivity.

More scientific research is under way, but many have thought that adult fish can withstand carbon dioxide pulses far higher than what is predicted for the foreseeable future. That is the good news. What some research has shown is that larval and juvenile stages of the same species face a much greater risk from exposure to carbonic acid at even low levels. A study by researchers Zofia Baumann, Stephanie
Talmage and Christopher Gobler exposed both egg and post-larval stages of estuarine silversides to CO2 levels about twice current levels. The results showed that for the post-hatch larval stage, this exposure reduced survival by 74 percent and length by 18 percent.

The egg stage was even more susceptible to impacts. So carbonic acid may not have very high impacts on adult populations, but if this research shows the susceptibility of a wider range of species in their egg or larval stages, then there is real trouble on the horizon. What if this adversely affects anchovies along the Pacific Coast or herring or menhaden along the
East Coast? These forage fish supply protein for a wide variety of fish species across a wide area.

Not all species will be impacted in the same manner. In some areas, the mixing caused by currents will, for the time being, mitigate some of the impact and cause some to think that this problem does not exist. We know the impact of acid rain on riverine environments and that minor drops in pH cause big problems. While some of that has been mitigated by air-quality controls, as well as chemical neutralization, the
same things do not apply to the ocean as a whole. Although in the confines of estuaries, there may be some efficacy to neutralization efforts. No matter what is done around the earth to mitigate
increases, the atmospheric carbon dioxide levels will continue to rise for the foreseeable future. While I wish that I had a good solution to offer, I do not.

In some estuarine areas, there is another problem impacting our oceans. The run-off of nitrogen from the use of fertilizers and detergents both residentially and commercially is causing huge blooms of green algae and phytoplankton. These prolific algal blooms die off and release carbon dioxide, contributing to the chain reaction. We are at the front end of this major problem. While it may seem overwhelming, and it is, we need to understand what the impacts are and how extensive they may become. Without that, we will not be able to do anything other than watch. We are entering uncharted waters, and that is always concerning. While I hope that everything I have read on this trend is wrong, I am worried that this ocean assault is real and not going away.