I think your boat may have set up for a pretty long time? As said "bugs" will grow in Diesel
and only a bio-cide will kill them, but once you do kill them, be prepared for quite a few clogged filters. Best to add the bio-cide once you get to where you are going, wait a few days and have one of the fuel filtering services filter your fuel.
Once the bugs are dead and gone there are products that will keep them form growing, you would think fuel would have this already in it wouldn't you?
These bugs look like snot in a filter, like a slime, not dirt or rust