Sounds like a massive dumping of industrial contaminated waste water. But, is it from nearby on land, or delivered from tankers off shore?
I see an incredible preponderance of starfish with extra limbs and what looks like some kind of stag coral. I think the “die-off” was dumping. Maybe local fisherman got frustrated with starfish killing off all the shellfish; if they were particularly ignorant, that could even explain all the starfish with 6 or more arms... but then some species of starfish NORMALLY have 6, 7 or 9 arms.
So run a geiger counter over them. That would prove radiation.
And why not do all the testing before running a panic story?