Examples of coexsistence in the euphotic zone?

I'm doing a marine ecosystem project and I have to include at least 2 examples of coexistence and cooperation in the form of predator/prey, parasitism, or mutualism. I've looked practically everywhere and can't seem to find a thing. Please list where you found your information so maybe it can help me with the rest of my project. Thank you!
Asked Nov 23, 2013

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