The first oil-tanker came and found the sea, entered a cove that the captain logged as flooded by cyanobacteria, by toxic algae, for though there was oil-sign, it was dim in the scarlet waters. This oil-tanker left the beach and did not return.
Only thing I saw. Not exactly sure if this breaks any grammatical rules, but it definitely doesn't sound right in the mind. I almost wanna say it's a run-on? I'm a terrible proof-reader, sorry.
Imagery: Dang, that was pretty good. I see sunsets, a beautiful coastline, perpetually streaking comets, a lively undersea ecosystem. As moments it does get lost, but it does work. I think that sometimes the description of this imagery is a little heavy-handed, and that's where it's at its worst (only comparably, it's still quite good). Less can, in moderation, be more.
Narrative: Makes sense. No such thing as too simplistic, it's execution that matters. I'm loving the theme.
Lines: Works very well. When the narrative is thick and full of life, the paragraphs reflect that. When life is short, choppy, and coming to an end, the paragraphs reflect that. Nicely done, if this is what you even mean by line editing.
Title: Hm. Title could use some work, in my opinion. While it, in present state, works just fine, I'll say it isn't really.. pizzaz-y enough? Maybe something like 'Snapdragon Sky'? Up to you.
Additional comment: While I like the connection to the present, and the second person bit at the beginning and end, they need to be separated from the main text in some way, so the reader can differentiate between the now and the then. A dash line? A separate font? Italics? There are many ways to do something like this.
Liked this one! Can't wait to see how it unfolds.
As always, don't let my crit change the direction of your story. All stated here is opinion and should be taken with a healthy dashing of salt, as I am not a professional.