What do you think is the primary reason why the Unionid mussel population declined whenever there is a dramatic increase in the Zebra mussel

When the Zebra arrived they ate all the food so the Unionid mussels declined as they died from the lack of food. Causing the Zebra Zebra numbers to increase and Unionid numbers to decline.

c- cold periods in earth's history during which glaciers covered much of the surface.

explanation:

that's what i got you can count the number of atoms