Steel in K2 requires wood (because of coke), but starting on Gleba doesn't give you access to wood. One possibility would be to forage for tree seeds (since the greenhouse isn't Nauvis-locked (if you provide a chemical plant to get sediment for stone)). Alternatively, I could see a case for making a Coal + Carbon recipe for coke if you start on Gleba.

I remember a "Gleba water cane" mod (unsure about the real name). These water-based sticks are just like wood and fit well in the Gleba swamps. That could kickstart this wood issue. Alternatively, some other Gleba native plants could get a wood drop.
In both cases, the question remains: how does that fit into the "seablock" theme, where anything around one is water (or lava)?

the question remains: how does that fit into the "seablock" theme

I don't see where the theme problem is coming from; we can already forage for wood on Nauvis and Gleba (without seablock) has decorative watercanes that provide wood. We can just forage through the reeds for wood (or cane seeds), perhaps at a slower rate than driftwood on Nauvis b/c the canes give less wood than trees.

1.7.5 should now resolve this.
Driftwood Forage is extended to Gleba - whether you're playing APS/K2SO or not. I agree with the premise that since there are wood-bearing trees on Gleba, it makes sense to be able to forage for wood. Not worth introducing an entirely new recipe for the Gleba version.
Also, if you're starting on Gleba with APS, you get a few chemical plants in your starting stockpile for access to early stone.