Are you concerned about DOC?

[Subsea]

It’s an interesting, but also somewhat concerning result if one is hoping for high DOC removal effects from sponges in a reef tank.

The concerning part is the claim that more than half of the organic C consumed is assimilated. While that might be assimilated into bacteria which then are released again (which begs the question: are the sponges actually needed for that process), but if the C is going into sponge tissue, then I think this is bad news for sponge proponents.

Those promoting sponges have sometimes claimed that even a little sponge processes a lot of organic. But that cannot be true if half of what they consume is incorporated. The small amounts (by mass) and the slow growth rate of cryptic sponges in reef tanks means the total organic removed is only twice the mass of the sponge over the entire time it was there. If true, that is not very much.

While I can’t find the link, yet, part of the research that addressed your point was “sponges would double in biomass every 24 hours but for the energy rich detritus shed off and made available to the microbial loop”. I use cryptic refugiums & live rock to feed diverse filter feeders.

For me, nutrient export is not a desired goal, in fact, I dose ammonia. I prefer nutrient recycling as I seek to maintain diverse filter feeders and for that purpose a cryptic refugium works for me. However, cryptic sponges grow on dark side of rocks in display tanks.

PS: Considering that cryptic sponges consume DOC & POC and produce energy rich detritus that feeds the microbial loop, which is significantly more diverse than bacteria, so I value their contribution to biochemistry that converts pollutants into food for desirable filter feeders. However, I can’t measure their individual contribution.