Probably a lot more than that given the population densities suggested in the article.

"1 million mussels died in an area the size of a tennis court."

I think they usually measure small things in terms of mass. Here is a report just for Pugent Sound that suggests annualized reproduction of about 850,000 kg.

http://www.pacshell.org/carrying-capacity.asp

I agree:

>1 million mussels died in an area the size of a tennis court.

So, it could be as small as 1000 tennis courts or less then 6.5 acres.

Most likely it was spread over a larger area and this was a spot with a lot of life that got hit hard, but it is a frame of reference

Exactly!!! These articles are just click baits. If we cannot compare this to previous data then this is just opinionated.