Capabilities of macroalgae

Hi folks,
Reading a discussion over at a swedish reef forum about deep sand beds and macroalgae a few questions came up:

What are the capabilities of the macroalgae rhizoids? Do the algae create microenvironments around their rhizoids, for instance using a protonpump to lower the pH thus gaining a local advantage? Oxygen ejection or CO2 absorbtion?

Are there any internal transport mecanisms in unicellular macroalgae?

References gratly appreciated!
cheers
Mattias