Since the industrial revolution, humans have been pumping carbon dioxide and other harmful gasses into our atmosphere as a by-product of our dirty energy sources. Thankfully, it is now widely accepted that these emissions are having devastating effects on our planet, most notably the changing of our climates. Around a quarter of these emissions (24 million tons of Carbon per day) are absorbed into our oceans. Our governments told us that the oceans were helping to alleviate the issues of climate change by absorbing our harmful gasses. However, it is not until recently scientists recognise the fact that the ocean is under stress and by absorbing these gasses could be slowly dying.
The mass absorption of carbon into the oceans is causing them to become more acidic. Scientists have coined the phenomenon Ocean Acidification (OA). Acidification shifts the equilibrium of carbonate chemistry in seawater, reducing pH and the concentration of carbonate ions in the ocean. CO2 reacts with water particles to form carbonic acid. Carbonic acid then dissociates to form bicarbonate ions and hydrogen protons. These hydrogen protons, which are corrosive to carbonate, then react with carbonate ions (CO32-) to produce more bicarbonate ions. This cycle reduces the availability of CO32- in the oceans which is required by many organisms for calcification (growth of exoskeletons).
The oceans have a history of changing chemistry, usually the erosion of chalky cliffs and rocks are enough to balance the changing carbon levels and keep the ocean at a stable equilibrium. However, humans have been pumping these harmful gases into our oceans at a rate never seen before. By 2100 the ocean will be at its most acidic point for 800000 years, the rate of change is the highest it’s been for 300 million years. This means our planet is struggling to cope with the rapid change, and we are not sure what it means for our ocean communities.
The most obvious effect of OA is on those organisms that create their skeletons out of calcium carbonate (CaCO3). Increasing OA decreases the availability of CaCO3, reducing the ability of reef-building corals and shell fish to produce their skeletons. Organisms such as sea snails, sea urchins and zooplankton will have reduced ability to maintain their protective shell. When carbonate concentrations fall below their saturation threshold, structures made out of CaCO3 will begin to dissolve.
Many of these organisms which rely on CaCO3 are the basis of most marine food webs. Almost all crustaceans and fish have larval stages, we call these organisms zooplankton. Reduced ability to grow their skeletons will damage their populations dramatically. Almost all marine food webs rely on these zooplankton for their energy, if we lose zooplankton then the populations of their consumers could collapse. A dramatic effect on some calcifying species, including oysters, clams, sea urchins, corals and calcareous plankton has already been noticed, leaving many food webs at risk.
Perhaps the most worrying issue is that of the reduced ability for coral reef systems to build their hard skeletons. Coral reefs are home to millions of aquatic species and are relied upon for the majority of sea water food webs. If coral reefs continue to be destroyed then the ocean as we know it will be lost. It looks like we are reaching a point where coral reefs erode faster than they can be rebuilt due to the lack of CaCO3 availability in the water.
Until recently most experiments on the effects of OA have been short term, lab based experiments. This means it is hard to get an accurate picture of the potential effects of OA in the natural environment, were much more variables come into play. However, recently scientists have started to take advantage of natural laboratories. Areas were volcanoes emit large amounts of carbon into coastal environments are now been heavily studied. These small scale areas offer scientists insights into how large amounts of carbon could change the ocean environment.
Unfortunetly, these natural experiments on volcanoes are giving pretty grim out looks. Some found that with a pH of 7.8 (normal is 8.2pH) calcifies were completely absent and there was up to 30% biodiversity reduction. Areas around these natural vents emitting CO2 showed no coral or sea urchins and seagrass dominated the areas. High CO2 and low pH stimulates the productivity of many marine photoautotrophs (seagrasses), studies of high CO2 communities near submerged volcanic vents reveal luxurious seagrass beds. This may sound like a positive but this drastically reduces the biodiversity of areas reducing the productivity of our oceans.
The destruction we are causing to our oceans through OA will come back to affect us humans as well. Today, more than a billion people worldwide rely on food from the ocean as their primary source of protein. Many jobs and economies depend on the fish and shellfish in our oceans. In recent years, there have been near total failures of developing oysters and other shellfish in aquaculture facilities around the world. If we are not careful we will destroy the food webs that actually are feeding us.
Ocean acidification is a relatively new field of research. While it is gaining some attention among policy makers, international leaders and the media, there is still much to understand about the issue itself and how it will affect not only the marine environment but the subsequent impact upon our society. It is clear that we are the ones who have created this disaster, it is also clear we are going to be the ones who ultimately suffer from it.
The problem is that OA is just one of the things devastating our oceans. This article has not mentioned the issues of ocean temperature rising, mass overfishing and habitat destruction that is happening all over the world. Our oceans are been attacked on so many fronts it is hard to see how we can solve these problems. The most worrying issue is the lack of discussion and coverage of these issues were it matters. Our earth is dominated by oceans and yet we continue to neglect and abuse them. It is up to us to make these issues at the forefront of our everyday discussions, if we show we care then we can start to influence our governments to do something to put this right, tighter regulations and sanctions must be put onto the global corporations who are still pumping these toxic gasses into our oceans. Let’s not sit back and watch our oceans die.