10. what would happen to the food web if all the plants were removed?

Explanation:

It would eventually break down and there would not be as much diversity. This is because carnivores eat meat, and herbivores eat plants, so since carnivores sometimes eat herbivores, neither would have any food.

the reason the two sea urchins don't compete with each other for food, resources, etc. is because the urchins have adapted to the environment but they have also adapted to each other. this is most likely because the genes of the sea urchins.