Mechanical energy is the sum of the energy of an object. A kinetic and potential B potential and thermal C kinetic and chemical D potential and chemical

Ibelieve the answer is weathering,hope my answer has you : ) 

The population of unionid mussels decreased after zebra mussels were introduced. zebra mussels competed with the unionid mussels for food. the zebra mussels were able to displace the unionid mussels, allowing the zebra mussel population to increase  over the years. the unionid mussel population decreased because  of lack of food.