The End of Earthly Oceans - Ocean Worlds: The Story of Seas on Earth and Other Planets - page 201

living in the world. So, other than the vortex and distarterops—what
might appear in the new oceans?
It is likely, as we have seen, that there will be a reef gap starting very
soon. Reef gaps, in the geological past, have mostly lasted a few mil-
lion years, before new reefs arose. Reefs tend to return in Earth his-
tory because, once formed, they are resilient, stable structures that
enable very many creatures to coexist in a self-sustaining ecosystem.
Reefs in the past have not all been coral-based. In the Palaeozoic there
were reefs built by archaeocyathids and stromatoporoids (extinct
organisms, both likely related to sponges). Reefs were also built, later
in the Palaeozoic, by bizarre, tubular brachiopods: the richthofenids.
These were good at what all successful reef-builders do—crowding
out much of the competition for space and food and sunlight by mass-
ing together to make robust frameworks. Then, in the Mesozoic, mol-
luscs followed the richthofenids by evolving the tubular rudist
bivalves, and made in effect copycat reefs. Stony algae have made
reefs, as have bryozoans (moss animals) too.
So what might make up the next generation of reefs, millions of
years from now? Corals might bounce back, of course—the hexacor-
als that still build modern reefs have done so at least twice in the past,
following the Cretaceous-Tertiary and Paleocene-Eocene crises. Per-
haps the molluscs might come up with new designs: some descend-
ant of the common mussel, perhaps, growing larger and moving
offshore and binding tightly with its kin to convert areas of the sea
floor into wave-resistant bulwarks. Or maybe the reefs of the future
will be barnacle reefs, the evolution of these organisms having been
given a helping hand by their struggles to cling to boats and resist the
efforts of boat-owners to dislodge them. Something will eventually
build reefs again, as long as oceans and complex life remain.
There will be many other niches to fill (and perhaps new niches
to exploit) in the new oceans. If sharks continue to be relentlessly