I believe there are some photosynthetic sponges, but I can't find any good information on which are and which aren't (or finrm confirmations of that statement). I've got a blue one (may be a Haliclona sp?) that I've had for over a year and with no additional feeding, it has been growing pretty well. Not lightening fast, but 3-4x bigger than when I got it last Sept. It likes to be in light, too, so I wonder if it may be photosynthetic. There are a few books out there, bt I've not gotten my hands on any yet. I've also just picked up an orange finger and a red finger (different Genera though, I think). I've only had it two weeks now, but the orange is still looking pretty good (the red has a few lighter spots where it appears to be not doing as well). I'm hitting them with a ton of flow (more laminar than turbulent, as with gorgs). Been feeding phyto (have several non phototsynthetic gorgs in that tank, too-and that's my SPS tank
). If in a years time I've been able to cut frags (that also continue to grow for me), I'll feel like I've had success with the orange and red.
Air is only a problem if it gets trapped in the body. I try to limit the exposure to air (transoporting in a completely full bag, transferred under water, etc.). However, if they get exposed to air, give them a thorough swishing underwater to help remove trapped bubbles. I know someone who has been fragging and growing sponges for a while, and he said he'l chop them up when he gets them to try to improve mortality rates. I don't know if his theory is that smaller pieces are easier to remove air from, or if smaller pieces just do better. I probably respect him more than anyone else I've known in the hobby, so I'm following his experiences.
