The problem is that it's impossible to do a test in a lab. We've been doing algae growth experiments for decades. However, in a real exosystem, you have to look at the effects of ocean currents, predation, larger food web interactions and so on. We don't have any sort of laboratory even remotely large enough to properly simulate this sort of thing. The only way we can test this is to do it in the actual ocean which is problematic.