Activity: Ocean acidification and eggshells

Ocean acidification and eggshells (20 pts)

Introduction/background

There is scientific evidence that suggests that the pH in our oceans is decreasing and therefore the oceans are becoming more acidic. This could have significant impacts on life in the sea.

For example, many marine species rely on calcium carbonate (CaCO3) to build a shell or skeleton. One of the effects of increasing acidity is a reduction in the availability of carbonate. This means that any animal that produces a calcium carbonate shell or skeleton will find it much more difficult to do so. Organisms could grow more slowly, their shells could become thinner or they might dispense with shells altogether.

A typical chicken eggshell consists of about 94–97% calcium carbonate, so this experiment uses chicken eggs to simulate the potential effects of acidity on marine animals. As with shelled marine animals, eggshells vary between different species and vulnerability to acidity will vary with shape, thickness, structure and so on.

pH and ocean acidification

pH is a measure of the acidity or alkalinity of a solution. Pure water is said to be neutral. The pH of seawater is about 8 but this varies slightly throughout the world.

The world’s oceans currently absorb as much as one-third of all CO2 emissions in our atmosphere. This causes the pH to decrease, resulting in the ocean becoming more acidic.

This could have significant impacts on life in the sea. For example, many marine species rely on calcium carbonate to build a shell or skeleton. One of the effects of increasing acidity is a reduction in the availability of carbonate. This means that any animal that produces a calcium carbonate shell or skeleton will find it much more difficult to do so. Organisms could grow more slowly, their shells could become thinner or they might dispense with shells altogether. It is difficult to predict the overall impact on the marine ecosystem, but many scientists fear that ocean acidification has the potential to decrease marine biodiversity on a very large scale.

Links to New Zealand research

Abby Smith is a biogeochemist at the University of Otago. Part of Abby’s research involves working on different bryozoan species and investigating how they respond when they are placed in solutions with different pH levels. The results have shown that a decrease in pH affects the skeletons of bryozoan species differently, depending on what they are made of and the shapes formed by their colonies. These results mean that some species of bryozoans have the potential to act as ‘canaries in the coal mine’ and provide early warning signs for areas that are at greatest risk from ocean acidification.

What you need

3 eggs, ideally these eggs should be hardboiled to minimize any mess from this lab.

3 beakers, jars, bowls or cups. It will help to avoid spills if they have lids (container should have at least 300ml (or ~1 ¼ cup) capacity)

250ml tap water (or ~ 1cup)

50ml (or ~1/4 cup) vinegar. If you don’t have vinegar, substitute lemon juice.

50ml (or ~1/4 cup) household ammonia. If you don’t have ammonia, substitute ~1/8 cup of liquid dishwashing soap.

Note: The amount of liquid required may vary according to the size of container used. 1cu=237ml

What to do

Watch the video clip Ocean acidification. Chicken egg shells, like the exoskeletons of many marine organisms, are made of calcium carbonate. We’re using the chicken eggs as a proxy for marine exoskeletons.

The question for this week’s lab is: Under what kind of pH (acidic, basic or neutral) do chicken eggs dissolve?

Write a hypothesis that address the question above that is aligned with the experiment that you’ll do which is outlined below:

Hypothesis (2 pts):

Set up and label 3 beakers:

Acidic solution: 100ml tap water (or ~1/2 cup) and 50ml (or ~1/4 cup) vinegar

Basic solution: 100ml tap water (or ~1/2 cup) and 50ml (or ~1/4 cup) household ammonia

~Neutral solution: 150ml (or ~¾ cup) tap water

Look under the ‘What you need’ section above for substitutions if you don’t have vinegar or ammonia.

Place 1 egg into each beaker (make sure the eggs are all the same size and from the same carton). Be sure to label your containers so as you watch the eggs you know which is in an acidic solution, which is in a basic solution and which is in a neutral solution. You can put the entire egg in, or you can peel the egg and just put the shell in. I recommend that you use the entire egg though.

This is Day 0. Record any observations and take a picture of your eggs at this time/Day 0 in Table I below in the Data section. Specifically, pay attention to whether there are bubbles, if the egg is floating or on the bottom of the container, the color of the egg, and the size of the egg. (Hint: You should observe bubbles, at least in the acidic solution)

In addition to these written observations, please include pictures of your eggs at Day 0, Day 1, Day 2, and Day 3 also in the Data section below. Day 1 is 24h after you set up the experiment. Day 2 is 48hr after you set up the experiment. Day 3 is 72h after you set up the experiment as well as the last day of the experiment. Try to put all of your eggs in the same picture, and be sure the treatments are labelled so I can tell which egg is in which solution.

Leave the beakers in a cool area for 24 hours. Observe each beaker again, record any changes in Table I under Day 1, and take pictures of your eggs.

Repeat for 2 more days (so 3 days/72h total). Be sure to record your observations in Table I each day and take pictures of your eggs.

Lift the eggs carefully out of the solutions and feel them. Record any differences from the starting egg under Day 3 in Table I and take a final picture of your eggs. For example, are the eggs hard or squishy? Do they still have their shell? If they all have shells, can you tell a difference in the thickness or fragility of the shells?

Data

Table I (6pts)

Day 0 Observations

(When you set up the experiment)

Day 1 Observations

(24h after you set up the experiment)

Day 2 Observations (48h after you set up the experiment)

Day 3 Observations

(72h after you set up the experiment)

Egg in Acidic Solution

Egg in Basic Solution

Egg in ~ Neutral Solution

INSERT PICTURES HERE (6 pts, 1.5pts/picture): Please include 4 pictures, one from Day 0, one from Day 1, One from Day 2, and one from Day 3. Each picture should show all of your eggs. Please be sure it is clearly labelled which egg is in which treatment so I can figure out what is going on with your experiment.

Discussion questions (6 pts)

How do you think ocean acidification might affect marine animals with calcium carbonate shells or exoskeletons?

How do you think ocean acidification might affect the marine food web?

Is there anything we can do to reduce ocean acidification?

http://sciencelearn.org.nz

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