This is not the first time sea floor microbes have been detected, but it is the first time that their abundance has been quantified. This paper reports thousands of times more bacteria on the sea floor than in the water above, at more than one study site.

This is not exactly right. Bacteria abundance and diversity have been documented many times from the deep-sea floor. This is the first time that they have been documented, or even thought of, on hard substrate (in this case basalt). The truly interesting comparison would have been between ‘typical’ deep-sea floor, a clay-like biogenic ooze, and the hard substrate samples.