I was surprised to see that fish or plants stressed at 100% do not die/decay/disappear.
This is obviously not easy to fully reproduce, especially the decay, but at least, they should die.

Some extra thoughts:
- they should not all die at the same time. Usually, this is not how it happens so there should be some randomness. The ability to withstand stress for a given period of time could also be influenced by factors such as size, amount of light (for plants) or age. That way, when some creatures die and lessen the burden on the ecosystem, the remaining ones have a chance of surviving.
- when dead, what happens to their body? do creatures create some decay of animal matter for a given period of time? what about plants?

More about the life cycle:
- plants and creatures can grow and die naturally
- some creatures can feed on plants this means that plants could be eaten and have corresponding marks
- we could add a system for diseases based on stress and other factors but this is probably for later and too hard to model.
- how about reproduction? creatures do not always reproduce in the same environment as they live (this is one reason why I want to have the ability to have both deep and shallow waters in a tank and my post about landscaping substrate) so this should be taken into account