In this wildly divergent Earth timeline, a group of diatoms evolved to be up to a few inches across (rather than 2mm or less). With this group presumably developing some similar traits to organisms like macroscopic unicellular algae and slime mold.
The diatoms in this group all share the following traits:
- Frustules are impermeable glass, with small openings which can be sealed shut with a trapdoor like mechanism. This means a giant diatom should theoretically be able to survive passing intact through the digestive tract of a whale (since glass can resist hydrochloric acid).
- Have anaerobic internal chambers which let them efficiently fix nitrogen from the air or water.
- Most of the diatoms volume is made of vacuules for storage and regulating bouyancy.
Diatoms can fix nitrogen, and get other nutrients by regularly descending into deeper waters. The combination of traits described means giant diatoms aren't limited by the availability of nutrients in the surface water like other pelagic photosynthesizers, so they should have a massive pelagic biomass.
Am I missing some obvious reason why large floating glass photosynthesizers like this are implausible?
Given the surface area issue any living parts of the cell will be no more than a few mm thick. Many will grow into connected clonal colonies, like real life diatoms.
If giant diatoms are feasible, then could fish, marine mammals, and reptiles plausibly evolve to prey on them?