“Benthic microbial fuel cell” is propeller-head code for the following very interesting fact: If you bury a metal plate a few centimeters beneath the ocean floor, and elevate a parallel plate a few centimeters above the ocean floor, the potential between them (due to ongoing microbial metabolism in the sediment) is enough to generate useful power. 800mV is a typical figure, but if I understand correctly, the current is directly related to the area of the plates, so the amount of power available by this method is theoretically only limited by the size of the plates you can install. Mark Nielsen is a doctoral candidate at Oregon State University under Dr. Clare Reimers, an expert in the field. This page at the OSU website provides a nice general overview of the concept and of Mark’s work in particular.
Endless sustainable power at the sea floor