Originally Posted by The Vorpal Tribble
As far as I know no spells count as direct sunlight, so light spells don't affect it.
I'd have thought the invisibility would have needed more of an RP reason...
Basically it fit my concept of the creature.
Actually, Sunburst (Druid8/Sor/Wiz8/Sun8) destroys Undead
who are specifically subject to damage and weakness from sunlight. It similarly deals damage (like it does to normal undead) to oozes, slimes, fungi and mold. I guess it sort of counts as replicating true Sunlight. I would rule that it does, as a DM.
By the way, I like the creature, but it does seem to lack a justification for being invisible. It seems to be somewhat extradimensional in the way that it produces seaweed from apparent nothingness. Just a thought, but it sounds sort of like it would be an interesting creature to have hail from the elemental plane of water.
I think that the natural invisibility would make more sense as a need to spot check it like a Gelatenus Cube when out of water. In water, it makes sense to be entirely invisible. Just some thoughts.