[Timfish]

@Karimwassif,
No worries, I keep rereading de Goeij's research to try to understand it all. I think though it's mostly the labile DOC that is being consumed by sponges and being converted into nitrogen rich detritus that is then quickly finding it's way into the food chain. The closed cavity experiments do show a decline in the bacterioplankton over time so it's resaonble to me sponges (and for new readers that haven't read earlier posts the sponge's holobiont or microbial simbionts) are feeding off them but he makes a point the POC (particulate organic carbon) which I understand to include microbes only supplies a fraction of it's diet. It's also important I think to point out de Goeij's research show's the inorganic nitrogen and phosphate sponges are producing and releasing into the water was fairly small.

@dz6t,
Yes, corals are grabbing whatever they can, both organic and inorganic and we need to think in terms of total notrogen, organic and inorgainc, and total phosphate, organic and inorganic. Not just nitrate and PO4. What we are learning is the microbial life is far more complex than we though even just a few years ago. A good place to start to learn more about the microbial roles with corals is Forest Rohwer's book "Coral reefs in the Microbial Seas".