The author has a master's in science writing, so it's surprisingly sloppy.
They did it again too: "The clone is about 1.5 orders of magnitude larger than the largest fungi [770 hectares] and the longest sea animal [120 metres]." It's over 3 orders of magnitude longer than that animal, and closer to 1.4 orders of magnitude larger area than that fungus.
But also, it's not a single connected organism anyway (emphasis mine): "a single polyploid clone spanning more than 180 km in fragmented, near-shore meadows".
The paper explains a little more the meaning of the 180km figure: "a single polyploid clone spanning more than 180 km in fragmented, near-shore meadows". So this seems to be the distance between the farthest two clone instances. It sounds like the clone instances were originally connected but became disconnected in time.
I think the Washington DC comparison comes from this line: "We used the total estimated area of P. australis meadows in Shark Bay (200 km2 pre 2010/11 heatwave [43])" compared to a DC area of 176km².
I don't think that means it was ever all connected at once though. Each meadow could expand and split over time.
Yes, the 200km² vs. 770 hectares is what I used to get my 10^1.4. It's unrelated to the 180km distance the author puts in the DC comparison sentence though.
They did it again too: "The clone is about 1.5 orders of magnitude larger than the largest fungi [770 hectares] and the longest sea animal [120 metres]." It's over 3 orders of magnitude longer than that animal, and closer to 1.4 orders of magnitude larger area than that fungus.
But also, it's not a single connected organism anyway (emphasis mine): "a single polyploid clone spanning more than 180 km in fragmented, near-shore meadows".