Best answer gets

a population of coastal fish show signs of die-off when there are no known predators or environmental stressors in the area. what is the most likely explanation for what has happened to this population?

the population reached carrying capacity for the area.
the population evolved with a shorter lifespan.
the population reached its emigration period.
the population evolved with new eating habits.

the most likely case would be that population reached the carrying capacity of the area.

Explanation:

Explanation:First off the population of the prey that is the "coastal fish" In this case will increase in population and acquire a greater area for their survival and will start to (die-off).when the predators in an area are reduced or get extinct this change triggers a reaction called as "tropic cascade" in the ecosystem in which the change in the predator population has affects on the food web.

For example :when the wolves were eliminatefls from the American west, there were changes in the elk population and the vegetation the elk ate.

Therefore both preys and predators balance each other.

answer and explanation;

volcanic rocks are igneous rocks which form from lava, molten rock which has been thrust out of a volcano onto the surface of a rocky body such as an asteroid, planet, or dwarf planet.  

plutonic rocks are igneous rocks which form from subterranean chambers of molten rock or magma. plutonic rocks make up the base of continental crust as well as oceanic crust. their slow rate of formation causes them to be coarse grained since there is plenty of time for large crystals to form before the magma solidifies into rock.

the textural difference is that plutonic rocks are more coarse grained than volcanic rocks. plutonic rocks are coarse grained while volcanic are fine grained ; glassey or fragmental. since fine and coarse are adjectives the decision as to whether a rock is fine or coarse grained is generally made on the bases of whether or not the individual crystals can be seen in most if the rock.