  The interplay between exctions and vibrations is considered to be a key
factor in determining the exciton transfer properties in light-harvesting
exciton transfer complexes. Here we study this interplay theoretically in a
model for exciton transport, composed of two chromophores coupled to an exciton
source and sink in the presence of vibrations. We consider two cases, that show
qualitatively distinct transport features. In the first, the vibrations are
global and affect the two chromophores simultaneously. In the second case, the
vibrations are localized on each chromophore. For global vibrations, the
current exhibits {\sl anti-resonances} as a function of the chromophore energy
difference, which are due to exciton-polaron interference. For local
vibrations, on the other hand, the currents shows tunneling {\sl resonances} at
multiples of the vibration energy. Counter-intuitively, both effects increase
with increasing temperature. Our results demonstrate that an environment can
either assist or hamper exciton transport, and are in accord with current
understanding of energy transfer in natural exciton transfer complexes.
