Mgreen500
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Question on how to measure plankton

Postby Mgreen500 » Tue Oct 17, 2017 10:32 am

Good afternoon,
My daughter was interested in doing a science fair project on the effects of sunscreen on plankton or possibly zooplankton. She was interested in how the coral reefs are possibly being affected by the oxybenzone. She wanted to do varying concentrations of sunscreen and see how the mortality or motility is affected. Is there any way to measure this in a reasonable way? Thank you

SciB
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Re: Question on how to measure plankton

Postby SciB » Wed Oct 18, 2017 6:18 pm

Hi,

That's a great idea for a project! Just about everyone uses sunscreen and then goes in the water at the beach. Some of the chemicals will end up in the water and the trace amounts could have an adverse affect on some types of plankton. The problem, naturally, is what organism to use to test your hypothesis.

Two single-celled marine plankton come to mind as possible test organisms for your project--dinoflagellates and cyanobacteria. The dinos are bioluminescent and you could measure the amount of light they produce as a readout for an effect of exposure to a sunscreen chemical: https://www.sciencebuddies.org/science- ... lagellates

The other potential test organism is marine blue-green bacteria, known as cyanobacteria. They are able to photosynthesize when exposed to light and produce oxygen gas that you can collect and measure as an indicator of the health of the plankton. Carolina Biologicals sells cyanobacteria cultures that you might be able to use for your project: https://www.carolina.com/living-organis ... nobacteria

I hope this helps you decide on how to do your project. Please post again with more questions and we can help you work out the details of the experiments.

Good luck!

Sybee

Mgreen500
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Joined: Tue Oct 17, 2017 10:23 am
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Re: Question on how to measure plankton

Postby Mgreen500 » Mon Oct 23, 2017 8:23 am

Thank you so much for the response. She likes both ideas, she is just not sure how she would go about collecting the oxygen and measuring it with the Cyanobacteria? Her methodology was using varying concentrations of oxybenzone sunscreen and seeing the response or possibly oxybenzone vs. zinc oxide.I assume for the dinoflagellates she would use a luminometer to measure the bioluminescence?

SciB
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Re: Question on how to measure plankton

Postby SciB » Tue Oct 24, 2017 7:45 pm

You're welcome! Glad to help.

Collecting and measuring a gas such as oxygen produced by algae is fairly simple. It involves growing the algae in a sealed container with a tube attached to the top. The end of the tube is put into a graduated cylinder full of water inverted in a bucket of water. As the algae produce oxygen the gas passes through the tubing and is emitted into the cylinder where it slowly displaces the water. After a measured amount of time you can read off the amount of oxygen produced from the milliliter graduations on the cylinder.

An illustrated explanation of how to collect and measure gas is given in a different Scibuddies project which uses yeast and collects carbon dioxide. That project is not the one your daughter wants to do, but the method for collecting gas would be the same. Here's the link to the gas collecting information:

https://www.sciencebuddies.org/science- ... #procedure

The project that uses bioluminescent dinoflagellates has you rank the brightness on a scale of 1 to 4, but this does not give an actual measurement. As you said, a luminometer would be the best way to quantitate the light emitted by a tube of dinoflagellates. If you have access to such an instrument by all means use it to measure the light intensity. Alternatively, there are apps that you can download for a smart phone that make it function as a light meter allowing you to read the intensity of a light source in some numerical units. I haven't used such a light meter app but if you go to youtube there are a number of videos about which apps are the best and what they can do: https://www.youtube.com/results?search_ ... meter+apps

Post again to let us know what you decide to do. We can help you with the experimental design and set-up and if you have any questions about procedures.

Good luck!

Sybee

Mgreen500
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Joined: Tue Oct 17, 2017 10:23 am
Occupation: Parent

Re: Question on how to measure plankton

Postby Mgreen500 » Thu Oct 26, 2017 9:27 am

Thank you for the information. She chooses to go ahead with the dinoflagellates since there are so many rules/regulations about culturing certain bacteria’s- she is doing this at home, not in the school lab. For her procedure she wrote out last night, she was going to set up one control dish of dinoflagellates with no sunscreen, she was then going to add 1ml of an oxybenzone based sunscreen to a group then also do a group with 5cc and 10cc. She was also going to to the same with a zinc oxide sunscreen. The dinoflagellates would be kept at the same temperature with a 12hr timed lamp. She was then going to measure the bioluminescence each night at 10pm. She was going to measure for 5 days. Her questions are do you think 5 days is a long enough period? Also should she just directly add the sunscreen to the dinoflagellates or we also ordered algal growth medium with them- should she dilute the sunscreen with that first prior to adding it to the dinoflagellates? Thank you for all the help.

SciB
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Joined: Fri Feb 01, 2013 7:00 am
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Re: Question on how to measure plankton

Postby SciB » Thu Oct 26, 2017 6:33 pm

Wow! You have done a lot of great planning of the experiments. I hope I can help you avoid any pitfalls along the way to producing some great data.

The dinos are pretty sensitive to their growth conditions--the temperature and the growth medium especially--so let them acclimate and grow for a while before you do the experiment.

Single-celled plankton like dinos respond quickly to changes in their environment so a five-day exposure to sunscreen should be long enough to see an effect on their ability to produce light.

There are a couple of things I'd like to suggest for you to do as part of your plan. Scientists have to think carefully about the conditions, the independent variables, that they choose for their test organism. They also have to define their hypothesis carefully as other scientists are going to review their work and pick out any errors.

For example, if a researcher were planning to do a test of sunscreen on plankton they would try to obtain the product with and without the test compound--oxybenzone in your case. In that way the dinos that will be the control are exposed to the same product as the test dinos except for the sunscreen chemical. If this is not done and you see an effect on bioluminescence then you cannot be certain that it was due to the oxybenzone and not some other ingredient in the sunscreen product. What I would recommend (and other experts please respond with your suggestions!) is that you mimic the way sunscreen would enter seawater by applying a measured amount to the inside of a small glass container, filling it with 100 ml of dino medium (https://www.carolina.com/biological-med ... /153757.pr) and allowing the liquid to absorb whatever leaches out from the sunscreen over a certain period--say two hours. Then you would pour the medium into a clean glass container and use that to expose the dinos.

Since you can't get oxybenzone by itself, why don't you try to get several sunscreen products with different amounts of oxybenzone or no oxybenzone and try the experiment with each. You still won't be able to prove that an effect is caused by oxybenzone because other chemicals are present in sunscreen products, but if the effect increases with increasing concentration of oxybenzone then you at least have suggestive evidence for its being the causative agent.

Let us know what you think of this idea. Also, remember to plan to have at least three cultures of dinos for each treatment so that after you do the light readings you can average the results and get a standard deviation. This statistical information will tell you whether or not the readings are valid. If you have time and enough materials I would suggest that you also plan to repeat the experiments. This really helps to strengthen the reliability of your data and convince people of your conclusions.

Keep posting and we'll try to answer your questions so you can get this project underway.

Good luck!

Sybee


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