According to the theory of matter proposed by john dalton:

1. all matter is made up of atoms
2. all atoms of the same element have the same mass
3. all atoms of the same element have the same size
4. combinations of atoms create chemical change

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.

The disturbance is only parallel to the motion of the wave.