Evolution of small things like algae and the krill which feed on it and feed the whale is quite fast. Single celled organisms reproduce on the scale of 20 minutes and hold immense amounts of genetic diversity in their populations to facilitate the success of a better adapted line almost immediately. Additionally, they are adept at horizontal gene transfer from other well-adapted organisms.
This would be great news if the whale literally only required krill to survive, but complex megafauna have complex needs, so the ability of krill and other small creatures to evolve is largely irrelevant in a discussion regarding the ability of megafauna to survive. This is especially true if you read TFA and see that the whales already adapt to eat different things as necessary.
My point is, for instance, that they need appropriate temperatures in the water. Again, nothing survives PURELY based on caloric intake. It does not matter much at all if krill evolve.
Right, this is my point. Looking at krill is looking at one PIECE of the stack. Other things support and interact with that stack. The stack is the whale. The point is that it doesn’t matter if this one single piece of the stack can evolve, it’s not nearly enough.
Algae are the bottom of the ocean food chain. Everything interacts with it. But algae's happy to grow in a bowl of water left in the sun.
Lots of things eat krill and small fish. They're near the bottom of the foodchain too. In addition to algae, krill are opportunistic omnivores who often consume detritus. But their primary diet is algae. Small fish tend to be pretty similar.
It's not that other things don't interact with algae or krill or small fish, it's that those groups are the foundation bedrock of the ocean ecology. And single celled organisms like algae are tough as nails in aggregate. Couldn't kill them all if we tried. Pool owners will be familiar with the struggle.
But it's not a bottom up interaction. If whales are killed off from climate change, then those other things can get out of control. Too much algae, and then you have hypoxic environments.
A perfect example of this is when sea otters were nearly hunted to extinction which caused sea urchins to flourish which caused the death of coral and coastal environments which started to affect the larger things that depended on those environments.
My point is that any change to the careful balance can have non-linear effects.
I think we're coming at this from different directions. The OP I responded to originally said: "Warming will kill off most of the systems these animals depend on within 30 years." which isn't what you're talking about. A top-down extinction looks like whaling in the 1800s and we already had that. Now they're on the mend.
