  We investigate, using the Hierarchy method, the entanglement and the
excitation transfer efficiency of the Fenna-Matthews-Olson complex under two
different local modifications: the suppression of transitions between
particular sites and localized changes to the protein environment. We find that
inhibiting the connection between the site-5 and site-6, or disconnecting
site-5 from the complex completely, leads to an dramatic enhancement of the
entanglement between site-6 and site-7. Similarly, the transfer efficiency
actually increases if site-5 is disconnected from the complex entirely. We
further show that if site-5 and site-7 are conjointly removed, the efficiency
falls. This suggests that while not contributing to the transport efficiency in
a normal complex, site-5 introduces a redundant transport route in case of
damage to site-7. Our results suggest an overall robustness of excitation
energy transfer in the FMO complex under mutations, local defects, and other
abnormal situations.
