What has more mass a whole sponge or that same sponge broken into tiny pieces

Well you see if the sponge is broken up or still together it has the same mass unless you are talking about a part of the broken sponge than that would be 1 out of the pieces and divided by the whole.

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.