I would like to avoid being labelled as a smart@ss but 1 cubic kilometer contains 1 billion cubic meters (of anything, say, water), so instead of 1/8th the true ratio is 1/8000.
At the same time – partly because of this disproportion – I do not understand the author’s worries. It feels like some paragraphs were cut or incidentally deleted from before the dire views at the end. So please, dear author, tell us how you came to your jellyfishy-sheeny scenario?

Thank you!

The article states that each unit could evaporate about 120,000 cubic meters of water per day. Changing that measurement into cubic kilometers yields about 1/8th of a cubic kilometer per day.

Here are two sources for consideration.

The first is an estimation of total evaporation on a 24-hour basis that has apparently been going on every day for a few billion years. This person estimates a little more than 1,000 cubic kilometers of total ocean evaporation occurs each day. So eight of the desalination units would total about 1/1000th of total ocean evaporation or about 1/10th of a percent. I expect that the resulting clean water would be utilized on land and would eventually return to the oceans by way of drainage or rainfall. So the net change in ocean water volume and therefore ocean salinity should be about zero.
Here is a link to one of many such estimates: http://www.madsci.org/posts/archives/2006-05/1148725781.Es.r.html

The second is a report from NASA that shows and explains the natural ocean water cycle.
I found both to be quite interesting.
I can understand that the author did not have space or time to go into a scientific explanation of the proposed desalination project, but I do not understand the basis for that last assumption.

Here is the link to NASA. Very informative website.
http://science.nasa.gov/earth-science/oceanography/ocean-earth-system/ocean-water-cycle/