MadSci Network: General Biology

Re: Do different oxygen levels in water effect Daphnia and why?

Date: Wed Aug 8 20:19:12 2001
Posted By: G. Monreal, Staff, Cardiothoracic Surgery , The Ohio State University
Area of science: General Biology
ID: 995624171.Gb

Hello Natasha!  Thank you for your question. 

You asked:  "I am currently doing a biology project studying the effects of 
different oxygen levels on Daphnia.  To carry out my experiment, I will 
measure the heart rate of at least 5 Daphnia at certain intervals, each 5 
Daphnia from one of the six different oxygen levels made up.  I need 
information for my formal write up of the experiment and am finding it very 
difficult to find direct info on how oxygen levels effect Daphnia.  My 
hypothesis is that lower levels of oxygen increase the heart rate of 
Daphnia.  What happens if the heart rate is increased?  How do Daphnia take 
oxygen in and use it?  etc.  It would also be of great help if you know of 
any similar experiments carried out."

Sounds like you're on your way to a good experiment!  First off, let's see 
how your study looks as an abstract (which is simply a brief summary of 
your experiment).  An abstract generally follows a format containing a set 
of steps:  
1. Title
2. Background (Why are you doing this project?  What is your main goal 
(your hypothesis))?
3. Methods (What are you going to do to the Daphnia in order to find out if 
your hypothesis is correct?)
4. Results (What did you find out?  What were the heart rates of your 
Daphnia at each oxygen level?)
5. Conclusion (Did your experiment prove that your hypothesis was correct? 
(it's OK if your hypothesis was wrong --- it is still data...)  Did you 
observe other changes that you had not expected to find?)  

Now, let's examine each step:

The Title will come last once you have acquired your data and come to a 
conclusion about your experiment. As for the Methods, you seem to already 
know how you are planning to carry out the experiment (writing up the 
Methods section tends to be the easiest part for all researchers, as you 
are simply describing what you have already done).  Once you perform the 
experiment, the results will come easily as well.  Even the data you 
acquire is completely the opposite of what you expected, or if all your 
Daphnia die tragically, or if you observe no changes whatsoever in any of 
your groups, your data is still data and needs to be presented.  The 
Conclusions will basically discuss how well your hypothesis stood based on 
what you and others already know about Daphnia physiology (specifically 
obtaining to their heart rate responses at different oxygen levels), and 
what you observed during your experiment.

So, based on your question, you seem to still need the following for your 
1. More info on Daphnia physiology
2. More info on what others already know regarding Daphnia physiology 
(specifically obtaining to their heart rate responses at different oxygen 

I did some searches on the net and found a bunch of different websites for 
you which may spark some theories for you to play around with:     
This site mentions that as water temperature rises, water loses its ability 
to carry dissolved oxygen... (Hint:  Think of opening a warm soda can as 
opposed to a cold soda can... Which fizzes more?...)
This site mentions that Daphnia are able to synthesize a particular 
molecule in an oxygen-poor environment...  (Hint:  What molecule carries 
oxygen?  What do Daphnia eat...therefore, what type of water are Daphnia 
most often found in?)
This site is a paper by S. Lass and colleagues entitled "How do Migrating 
Daphnids Cope with Fish Predation Risk in the Epilimnion under Anoxic 
Conditions in the Hypolimnion".  (You can also access this paper in the 
Journal of Plankton Research Vol 22 No.7, pages 1411-1418, 2000).
(Hint:  What eat Daphnia? they use their eyes to find the 
Daphnia?...if so, can the Daphnia hide in darker waters to avoid getting 
eaten?...doesn't the water get darker as you go deeper?...however, how are 
the oxygen levels in the water as you get deeper?...therefore, are there 
Daphnia surviving in this part of the water?...if so, how can they?...are 
they unhealthy here?)

Searching the MadSci website for more information on Daphnia will provide 
information on Daphnia physiology, including heart rates during various 
conditions. provides ton of general information and many 
links to other Daphnia websites that range from raising Daphnia for pet 
food to examining Daphnia populations in water-quality research.

Hope this helps!  Feel free to email me at if you have 
further questions as you progress with your research project.  I am also 
very interested in hearing how your study turns out!  Please keep me posted 
on what you discover!

G. Monreal 

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