Coastal ecosystems play an important role in marine life. They are home to several shellfish hatcheries and finfish, and they are highly productive. Within recent years, the effects of ocean acidification on coastal ecosystems have been apparent, especially pertaining to the shellfish that represent a large part of coastal organisms. In particular, scientists recognized both positive and negative outcomes on oyster populations in relation to calcification, growth rates and reproduction, and death rates.
The increasing amount of CO2 entering the earth’s oceans slowly decreases the pH level and therefore, affects the amount of calcium carbonate available to oysters. This compound is vital for many species of oysters in order for them to produce their protective shells. Over the past decade, ocean acidification has decreased calcification rates for many oyster species such as the Sydney rock oyster (Saccostrea glomerata), and the Pacific oyster (Crassistrea gigas). However, the Suminoe oyster Crassostrea ariakensis did not exhibit the same consequences. This demonstrates that while ocean acidification may be detrimental to some species of oysters, there are other species that exhibit little difference and may even thrive in oceans with larger concentrations of CO2.
Other research has been fulfilled to explore the impacts of ocean acidification on growth rates and reproduction. A particularly interesting study on Sydney rock oysters (S. glomerata) showed that elevated pCO2 negatively affected their larvae, resulting in an overall reduction of their growth, rate of development, and survival. However, when adult S. glomerata were exposed to elevated pCO2, their offspring were actually influenced in a positive way; They were larger and developed faster than S. glomerata not in waters with higher concentrations of pCO2. The results of this study suggest that it could be possible for oysters to adapt or acclimate over time to an environment with more pCO2.
Between 2005 and 2009, Pacific oyster hatcheries viewed drastic death rates. Whiskey Creek Shellfish Hatchery lost 75 percent of it’s oyster population in 2007, while Taylor Shellfish Farm’s hatchery was 60 percent below average in the year 2009. These large losses in oysters were primarily due to ocean acidification. However, natural processes also played a role in the outcome of oyster production per year. Taylor’s production in 2010 was it’s best ever because of winds that reduced the amount of upwelling and kept the surface waters away from waters rich in CO2.
Since Whiskey Creek and Taylor’s hatcheries were subject to major reductions in their oyster populations, the need for further studies became more apparent. The decrease in oyster productions had economic consequences because many people rely on oysters for their jobs. In 2010, the federal budget dedicated $500,000 towards monitoring CO2 levels in hatcheries. One popular monitoring device is the IOOS buoy, which allows people to truly look at the changes in water conditions. It was said that, “putting an IOOS buoy in the water is like putting headlights on a car.”
Although the affects of ocean acidification range depending on location, oyster species, and connection with natural occurring processes, it is clear that ocean acidification changes the conditions of oysters and other coastal organisms.
Ocean Acidification: A National Strategy to Meet the Challenges of a Changing Ocean. Washington, D.C.: National Acadamies , 2010. 68-72. Print.
At first, it might seem like a good thing that the oceans are absorbing massive amounts of carbon dioxide—about a quarter of all anthropogenic CO2 emissions. I mean, it’s slowing down global warming right? Not so fast. What many don’t realize is that even though the oceans are delaying atmospheric climate change, beneath the surface, dissolved CO2 causes enormous problems. Carbon dioxide forms carbonic acid when it dissolves in water, and the average acidity of ocean water has decreased from a pH of 8.2 to pH 8.1 since the Industrial Revolution. It may not seem like much, but because the pH scale is logarithmic, this 0.1 point decrease represents a 30% increase in the acidity of our oceans.
This increased acidity caused by our fossil fuel addiction means that we’re putting millions of aquatic species at risk. The situation is particularly worrying for species that use calcium carbonate to build their skeletons or shells, because the ability for these calcifying organisms to build their shells depends on the chemistry of the water they live in. These organisms range from phytoplankton, zooplankton and corals to molluscs, echinoderms and crustaceans. While there are exceptions, many studies of these organisms have found that an increase in dissolved CO2 and a decrease in pH results in decreases of average calcification rates and shell weights.
If this doesn’t seem like a big deal, then you should know that not only could this have rippling effects throughout oceanic ecosystems, but humans will be affected too. Or rather, humans are already feeling the effects, because ocean acidification has already reached economically important aquatic species. In 2007, oyster farmers in the Pacific Northwest discovered that their oyster larvae were dying like they had never seen before. The cause? The ocean water that the farmers used for their oyster tanks was so acidic that larvae shells were actually dissolving in it.
At one Washington farm, a shocking 80% of its oyster larvae died in 2009. The problem is particularly bad in the Pacific Northwest because of natural upwelling patterns, which brings up CO2-saturated water absorbed by the Pacific Ocean 50 years ago. Yes, you heard right. Water from 50 years ago, when CO2 emissions were much lower than they are today, is killing shellfish. Imagine how damaging the situation could become when the CO2 absorbed now resurfaces 50 years in the future.
In 2007, the total mollusc harvest is estimated to have been worth $15 billion. Some populations are especially dependent on shellfish— for example, New Zealand, Thailand, France and Chile rely on molluscs and other shellfish for over 10% of their protein. The subsistence fishers of small tropical island nations are even more vulnerable to changes in shellfish populations. Clearly, we should be concerned that our CO2 emissions are putting lives and livelihoods at risk through ocean acidification. If we don’t take action immediately, we’ll be harming more than just ocean life—humans will be feeling the effects as well.
Large bodies of water, like the ocean, act as a buffer for our atmosphere by absorbing a quarter to a third of all emitted carbon dioxide. This, at first glance, appears to be a way to slow the progress of global warming. In reality, it is simply another issue associated with increased carbon emissions. When carbon dioxide is absorbed in the ocean, it reacts with water to form carbonic acid, which goes on to dissociate into hydrogen atoms and bicarbonate. An increase in free hydrogen atoms is responsible for the increased acidity of the ocean, but also has most of the carbonate ions tied up in bicarbonate. Carbonate reacts with calcium ions to form calcium carbonate which is the main component in the shells and exoskeletons of sea organisms. With a decrease in carbonate ions, there is a decrease in calcification.
The consequences of decreased calcification are still being fully researched, but oyster hatcheries have seen less and less successful harvests the past few years. A study done by Oregon State University for Whiskey Creek Shellfish Hatchery showed irrefutable increases in ocean acidity. The study went on to show that an upwelling had brought up more acidic water from the bottom of the ocean. Some would argue that the bad harvest is simply a result of the upwelling and that acidification did not play a significant role. The major flaw in this argument is that this type of upwelling has always occurred and the deeper water has always been more acidic. Oysters are struggling to even make in out of the larvae stage because they are unable to accumulate enough calcium carbonate to make a suitable shell. This not only effects the two billion dollar shellfish business but effects the entire food chain of the ocean.
In order to combat this issue, Integrated Ocean Observing System (IOOS) buoys have been placed in the ocean where the water that is pumped into the hatchery comes from. The hatchery is now warned one or two days before very acidic water is coming through. Rather than having larvae in the water when this happens, they save money and resources by waiting to start their harvest. This has allowed them to continue to make money at a lower rate though. While they used to always be harvest oysters, they are limited as to when they are able to do that now. Before the implementation of the buoys, the oyster hatcheries were producing at twenty percent of their capabilities. Since they have been installed, the hatcheries are now functioning at seventy percent. For now, monitoring the situation has been enough to save the shellfish industry, but this may not be the case in the future. In order to ensure healthy shellfish for years to come, humans need to find ways to decrease their carbon dioxide output.
“Chapter 3.” Ocean Acidification: a National Strategy to Meet the Challenges of a Changing Ocean. Washington, D.C.: National Academies, 2010. Print.