Science Buddies: "Ask an Expert"

Hello, I have been conducting an experiment with Daphnia Magna and caffeine, and have approached an interesting problem. After exposing them to both Black coffee, and Monster energy drink, I have noticed that their heart rate have actually depressed and dropped in levels. How different are the metabolisms from human to daphnia? Any and all help is appreciated, thank you.

Hello,
I'm not really sure why that would be happening. I found this great article (http://www.nuffieldfoundation.org/pract ... te-daphnia) that goes a bit more into the science of how caffeine affects daphnia. It seems that past research suggests it would increase heart rate.
The only reason I could think of is if the caffeine is becoming toxic to them OR if they're in shock from the added dose. I would try doing a dose curve and adding various concentrations of caffeine, but starting off with a very lose concentration.

I hope this helps.