Ocean Acidification

I. Purpose

The purpose of this experiment is to determine the effect of carbon dioxide (substituted with pH) on the heart rate, mortality rate, pregnancy rate, and molting speed of brine shrimp. This experiment is motivated by the increasing carbon dioxide concentration in the atmosphere caused by greenhouse gas emissions. As carbon dioxide is absorbed by the ocean, the pH, in turn, lowers.

II. Introduction

Carbon Dioxide

The average carbon dioxide concentration in Earth’s atmosphere is 330 ppm. Carbon dioxide is released into the air by the burning of coal, oil, natural gas, or any fossil fuel. In our atmosphere, carbon dioxide levels rise 1 ppm per year on average.

One quarter of all atmospheric carbon dioxide is taken up by the oceans as it tries to reach equilibrium by direct air-to-sea exchange. This causes ocean turnover when the carbon dioxide dissolves in the ocean and takes long periods of time to fully deteriorate. With increasing carbon dioxide and rising acidity levels, all of these factors do not occur fast enough to control carbon dioxide buildup.

“The Biological Pump” transfers carbon dioxide from the oceans surface to its depths. The whole process involves the releasing of carbon dioxide from the heated surface water, and organism remains and feces-like matter being metabolized and released as carbon dioxide. This biological pump may stop functioning if the climate change affects plants. This helps the process as well. This means that aquatic animals will have to adapt to increasing levels of carbon dioxide in the ocean’s waters or die trying.

The global average temperature has increased over the last several decades and the atmospheric pCO² is also slightly higher than previously measured. This change indicates that Earth’s climate is hyper-sensitive to the pCO² changes that are occurring. Our oceans waters now have a pH of 7.91-8.33 suggesting that carbon dioxide is now inducing the ocean’s surfaces to heat. This atmospheric carbon dioxide is enhanced by climate sensitivity, which means the atmosphere’s warming patterns are a large factor. In relation, the ocean’s pH values now show large amounts of carbon dioxide in the atmosphere.

The burning of fossil fuels and the atmospheric carbon dioxide levels rising has the ocean absorbing more carbon dioxide to stay in balance. The oceans will absorb as much carbon dioxide as people pump out by burning fossil fuels. The oceans take in so much of it that global warming occurs and heats the waters. This slows ocean circulation which, in turn, causes the oceans to take in less carbon dioxide, thus leaving more of it in the atmosphere. For the ocean to take in carbon dioxide, photosynthesis in phytoplankton as well as carbon dioxide dissolving in water must react with the seawater to create carbonic acid. This carbonic acid releases hydrogen ions and when combined with the carbonic acid in seawater. This process forms bicarbonate, which doesn’t escape the ocean easily. The reaction lowers the water’s pH, making it more acidic.

With temperatures growing higher, carbon dioxide leaks out of the oceans. This carbonate must be restocked once used. The replacement comes from deeper waters rich in dissolved carbonate. The warmer surface water makes it harder for winds to complete ocean turnover and with a lack of fresh carbonate-rich waters from below, the surface water is left saturated with carbon dioxide. In turn, fewer phytoplankton take in carbon dioxide from photosynthesis, slowing the process greatly and decreasing the amount of carbon dioxide the oceans can take in.

Brine Shrimp

The scientific name for brine shrimp is Artemia salina. They live in isolated bodies of salt water and feed on microscopic organisms such as algae, yeast, and bacteria. Brine is a salt solution, hence their name, and they are aquatic crustaceans. Brine shrimp can withstand wide changes in temperature because they have the ability to regain practically all of their intercellular water. Geographical location and water quality are important factors in determining their composition of fatty acids, proteins, pesticide concentrations, and other substances.

Brine shrimp are less than 1cm in length, and their bodies have wings along their sides with eleven pairs of appendages that undulate and act as paddles. The female of the species develop live young or eggs in her sack and the first batch of babies are born live. The live larval brine shrimp are also called Nauplii. They grow well in favorable conditions with good food, oxygen levels, and the right salt concentration. It takes three to six weeks for the shrimp to reach full maturity.

Brine shrimp must live in salty waters, and are suited for living in an array of salt concentrations as low as 25 ppt and as high as 300 ppt. The best salt concentration is 80 ppt, which is twice as salty as the ocean. Artemia cysts can stay dormant for long periods of time and can be easily hatched. They make valuable research organisms with short life spans that require very little food. Brine shrimp are an important food source for fish and crustaceans in home-based aquariums, aquaculture systems, and labs. The larvae or nauplii hatch in a few hours when added to water. When grown they have eleven limbs and can change colors in their transparent looking bodies.

The life cycle of an Artemia begins with the hatching of cysts which are encased embryos that can stay in their dormant state for years if kept dry. If they are in 25°C temperatures, after 15-20 hours, the cysts burst open and the embryo leaves the shells and hangs beneath it, still in a hatching membrane. This stage is referred to as the naupliar stage and soon they emerge as free swimming creatures. In their first larval stage as nauplii, they are a brownish orange color and do not eat because their mouths and anus are not fully developed. By the second larval stage, after 12 hours, they molt and filter feed on particles of different microalgae, bacteria, and detritus. They molt through 15 molting cycles and they can reach full adulthood in eight days. If the nauplii are kept in low salinity waters and optimal food levels are provided then pregnant females give birth to free swimming nauplii in ten to eleven broods over the course of their 50 day life spans.

Adults growing and cyst hatching should be done at optimal temperatures of 25-30°C. The preferable salinity is 30-35 ppt but they can live in fresh water for about five hours before dying. A pH of more than five and less than ten is also suitable for the Artemia to ensure no fatalities. Minimum amounts of light are needed for hatching and oxygen levels in the water are very important because it dictates what the brine shrimp will eat. With a good oxygen supply, the Artemia will be a pale pink, yellow, or green. Any waters with low oxygen levels will have large amounts of organic matter and high amounts of salinity from evaporation. This causes the shrimp to feed on bacteria, detritus, and yeast cells; then they will produce hemoglobin and turn red or orange. If this occurs, they reproduce dormant cysts and may cause the colony to crash. The foods the brine shrimp will eat should be decided based on digestibility, solubility, and particle size.

If good food levels are to be maintained then frequent feedings or continuous drip feeding are required. Some choices would be: micronized rice bran, whey, wheat flour, soybean powder, fish meal, egg yolk, and homogenized liver or dried microalgae such as spirulina. When the Artemia eat, the food isn’t directly consumed. Instead, the food is transferred to the mouth in a package-like form. As the space between their legs widens as they move forward, water is taken into this space where tiny filter hairs collect the food particles from the steady stream. On their backstrokes, the water is forced back out leaving the food remains at the base of their legs. There, glands secrete adhesive material that clumps the food into package form. The micro-hairs then move the food toward the mouth. On a final note, having good circulation, correctly distributing the animals, and giving them strong aeration are all important factors for raising Artemia.

III. Variables

Independent Variable: pH of the water

Dependent Variable: mortality, Pregnancy rate, heart rate, and molting speed

Control: pH 8.2, because it is proper pH, and, according to research, the best pH for raising Artemia salina

Constants: volume, type, temperature, salinity, and aeration of water; volume and type of salt in the water; amount of light; amount, type, and time of receiving food; number of shrimp per tank; mass of eggs and time when placed in water; time of tank cleaning; where shrimp are kept during cleaning; type of equipment used.

IV. Hypothesis

If the pH of the water is tested across a range of values (pH 8.2, pH 7, pH 6, pH 4), then as the pH decreases, the mortality rate of the brine shrimp will stay constant, the pregnancy rate of the brine shrimp will decrease, the heart rate of the brine shrimp will decrease, and the molting speed of the brine shrimp will decrease.

The mortality rate will be constant throughout, but other variables will change significantly as the pH lowers down to pH 4. Because the brine shrimp are not familiar with a pH lower than 5, but are able to withstand environmental stress, they will be able to survive in pH 4 but not function properly. They will adapt, but not completely. For example, their heart rates will slow drastically; they will molt slowly, or not reproduce properly due to low pH. In other words, they will adapt but mutate as the pH decreases.

Independent Variable: pH of the water

Dependent Variable: mortality, Pregnancy rate, heart rate, and molting speed

Control: pH 8.2, because it is proper pH, and, according to research, the best pH for raising Artemia salina

Constants: volume, type, temperature, salinity, and aeration of water; volume and type of salt in the water; amount of light; amount, type, and time of receiving food; number of shrimp per tank; mass of eggs and time when placed in water; time of tank cleaning; where shrimp are kept during cleaning; type of equipment used.

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peppy, HubPages, 12 February 2011. Full article.