Turns out these structures were floating masses of coral, reefs of the stuff. These microscopic creatures would latch onto any particulate they could to anchor themselves and start making coral masses. Then once they grew big enough would start producing hydrogen and float up. Sorta like snowflakes?

They sorta sit as a foundation/keystone species. Almost all higher order life on this planet is involved with these coral reefs. I mean, some of these reefs span the sizes of continents. And its interesting because these structures are so light and strong think aerogel capsules filled with hydrogen.