Changes in Marine Habitats

Oceans are a principal basis of life on Earth, and we are damaging them – fast. Specifically, ocean acidification is wiping out reefs and other organisms, and will soon affect many aspects of our lives. One quarter of all ocean life depend on reefs for food and shelter. Considering that reefs cover less than one percent of the earth’s surface, and less than two percent of the ocean floor. Coral reefs are also known as the rainforests of the sea because of how diverse the species that reside there are. We are facing a huge issue in our point in time. Our oceans absorb a great amount of carbon dioxide emitted into the atmosphere from human activity in which negatively effects on shell-forming organisms. So, not only do these chemicals affect the climate, but they also affect a great part of ocean life. Ocean acidification is the intake of CO2 by the world’s oceans, decreasing the concentration of carbonate ions, the state of calcium carbonate minerals, and the pH (therefore increasing the acidity). When the ocean absorbs CO2, the water becomes more acidic. CO2 reacts with water molecules to form carbonic acid which then breaks down into a hydrogen ion and bicarbonate. All of these hydrogen ions being present, is what then acidifies the ocean, and lowers the pH. pH is essentially the measurement of acidity in a solution, and is measured on a scale from 0 to 14. pH at 7.0 is presented to be the normal level, but, anything below 7.0 is considered acidic.

This photo indicates the process of ocean acidification as CO2 chemically reacts with H2O, causing it to become carbonic acid, or H2CO3. The water then becomes more acidic as the carbonic acid breaks down into a hydrogen ion, or H+, and bicarbonate, or CO3 2-.

Ocean acidification reduces the amount of carbonate, a key component in sea water. Most importantly, this makes it more difficult for marine organisms to form shells. The chemical reactions between carbon dioxide and our oceans make it more difficult for marine calcifying organisms to form shells and skeletons, and also existing shells become vulnerable to dissolution. Wherever there are marine calcifying organisms, there are risks from ocean acidification. The impacts of acidification will eventually make its way through the food chain, affecting economic activities, such as: fisheries, aquaculture, and tourism. A rapid pace of acidification will influence the extent to which calcifying organisms will be able to adapt, which is very problematic.

In chemical equilibria, when a species is added to the equilibrium, the chemicals react to keep the system in balance, in equilibrium. Hence, if a species acting as a reactant is added to the system, more product will be produced. In the chemical equilibrium for ocean acidification, CO2+CO3^(2-)+H20=2HCO3^(2-), one can see that an increase in the amount, or concentration, of CO2 in the ocean will trigger an increase in species 2HCO3^(2-), an acid. An increase in the amount of H+ ions, present in the HCO3^(2-), lowers the pH of the ocean. The pH of the ocean has fallen 0.1 pH units, representing a 30% increase in acidity. With the addition of a reactant, more product will be produced, and less of the other reactants, meaning less CO3^(2-), carbonate ion, being produced.

Carbonate ions are the backbone to much of the life in the oceans, those relying on calcium carbonate material. Calcium carbonate makes up the shells of calcifying species, like oysters, clams, sea urchins, shallow water corals, deep sea corals, and calcareous plankton. Reef-building corals and animals with shells lack the materials to build their own skeletons, and existing shells face risk of dissolving in more acidic waters. Coral reefs become more susceptible to damage in general, like storms or temperature changes, and their recovery time is prolonged. Supporting the most diverse multitude of plants and animals in the ocean, coral reefs are known as “the rainforests of the sea.” When such a large part of the food web of the ocean is affected, everything is affected.

Shells + skeletons of marine organisms/animals can become less dense/strong when exposed to ocean acidification. With coral reefs, this may make them more vulnerable to storm damage + slow recovery rate. Mollusks shells, for example, dissolve under acidic conditions. After fourty five days, the shell almost completely dissolves when placed in seawater with pH and carbonate levels under 7.0.

Every organism- from plankton, to fish, to aquatic plants- is affected by ocean acidification. As previously mentioned, shelled organisms are the most obviously affected, with their shells weakening and even disintegrating in acidic waters. Plankton, as previously mentioned, are dependent on calcium carbonate, and are the basis of the entire food web of the ocean, sustaining organisms from tiny fish to the ocean’s largest animal, a blue whale. Pteropods, pictured below, are disintegrating, and are a critical component to the diets of birds and fish. Not only are so many organisms affected by the state of shell-building organisms, meaning a lack of food and habitats for many aquatic organisms, but the raised acidity impacts them directly as well. Fish can become afflicted by acidosis, an oversaturation of acid in their blood. In order to reach equilibrium with the water around them, their cells take in carbonic acid. They then need to use energy to expel acid through their gills, kidneys, and intestines to return their blood to a normal pH- energy that needs to go to finding food, digesting it, reproducing, and escaping predators. Even their brains can be affected; clownfish, in more acidic waters, fail to flee threatening noises the way they usually would, swim farther from their homes, and struggle finding their way back. A certain type of algae, coralline algae, also builds its “skeleton” out of calcium carbonate. Coralline algae is made of a high-magnesium calcite form of calcium carbonate, even more soluble than regular calcium carbonate material. This algae, as you may get from the name, helps support coral reefs, specifically helping cement them to the ocean floor. A study by geologists and biologists found that coralline algae in acidifying conditions covered 92% less area than in regular conditions. This means more space in the sea for non-calcifying algae, which can smother and destroy reefs. It also means much, much less places for coral larvae to settle and grow. No part of the ocean is safe in increasingly acidifying conditions. Human life revolves around the ocean. It provides much of the oxygen we breathe, much of the food we eat, much of the money we spend.

Why are mollusks in particular important to the marine life? Mollusks are a big aspect in the marine ecosystem. They are home to many species of soft-bodied animals. Some include: snails, sea slugs, and clams. Not to mention, mollusk shells provide shelter for the food us humans eat. Even though there are many subgroups of mollusks, we actually have three major groups in which we classify the foods that end up on our dinner table such as squid, clams, oysters, mussels, scallops, and/or octopus. These three major groups are: the Gastropods, the Bivalves, and the Cephalopods. In conclusion, mollusks provide a home to many marine organisms and animals that not only us humans eat, but other bigger fish in the ocean, such as whales, eat as well. We rely on them for food, cleansing the water and making it healthy, and recycling any plant or animal waste.

“We find that oceanic absorption of CO2 from fossil fuels may result in larger pH changes over the next several centuries than any inferred from the geological record of the past 300 million years, with the possible exception of those resulting from rare, extreme events such as bolide impacts or catastrophic methane hydrate degassing.”  This strongly implies that humans using fossil fuels to power their society are responsible for the ocean acidification. As the main cause of this drastic shift, we ought to own up to our mistakes and come up with a solution to this problem.

National Geographic built on these findings, explaining how bad this problem truly is, with even the water chemistry itself morphing into a toxic being at the cost of our harmful behaviors that drain the planet.

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