I've seen distictions made between "Turf", "Macro" and "Folacious" algae but like Steve said they are vague terms. I saw a presentaiton a couple years ago by Dr. Haas who's looked very closely at the relationship between algae, microbes and DOC and he had a chart of the DOC production of 6 or 7 algae genus. What we call "hair" algae was at top with huge DOC output compared to Halimeda spp and chaetomorpha spp. which was at the bottom. (I haven't found it online but it might be
this paper I haven't bought yet.) One of the contradictions his research team found was on reefs completly over run by algae DOC levels were far below helathy reefs and in some samples was undetectable. Dr. Haas discusses how algae promotes heterotrophic microbial growth in this
Science Direct article Looking at Dr. Haas research (and Dr. Rohwer's "Coral Reefs in the Microbial Seas") along side Steve's and Dr. de Goeij's it easy to see just how critical cryptic sponges are in maintaining beneficial microbial populations in our systems along with healthy DOC types/species and levels.
Looking at Karim's feeding and maintnenance regime it's seems to me to correlate to what happens on reefs. Algae grows and releases DOC that promotes heterotrophic microbes. Herbivores eat the algae that Karim has harvested. The fish release ammonia, urea (and amino acids?) and phosphate into the water. Corals compete with the algae by soaking up and ingesting the ammonia, urea and any amino acids and phosphate to feed their symbiotic algae. Corals release DOC that promotes autotrophic microbes. Cryptic sponges remove DOC released by the algae and sponges and remove both heterotrophic and autotrophic bacteria that's feeding on the DOC. Sponges convert the DOC into nutrient rich detritus that feeds the filter feeders in the system (and releases small amount of inorganic nitrogen and PO4). Since there is a net increase in the coral biomass versus the algae biomass the microbial populations shift towards autotrophic types. And instead of tides and currents to help keep refractory DOC at acceptable levels water changes remove the refractory DOC that builds up over time.