If you look at the video in the article, there's a dude poking a hole with his boot in one of the smaller bubble. It looks like a possibility to capture the gas, maybe drill from top on the smaller ones and from side or bottom on the large ones... but, I'm not an expert. Also, top comment here linked to a conference where they've showed a submerged Siberian plane bubbling gas from beneath sea surface - 500 to 5000G of Methane. So long, and thanks for all the fish :/

I saw that video. It makes me think that the individual bubbles aren't big enough to be cost effective to harvest.