Well, it’s scientifically accurate that as abundance and diversity has decreased in our waters, it hasn’t been an opportunity for other species to fill in the gap so to speak.
We are seeing some warmer climate sharks moving further north, but that isn’t helpful to the foundation of our food chain. We do have invasive species of mollusks which have set up camp here permanently, but they seem to suffer and decrease in number just as the native species do. There are invasive crabs, but again, they aren’t about to patch the holes in this system.
Also, it’s important to note that our winter temperatures still hit 6 or 7 degrees Celsius. There are no warm climate creatures I know of who can move in during a hot summer and stick around for winter. That means our previously stable, temperate environment doesn’t appear to be able to be likely to host many creatures in any migratory range I know of.
I’m not a marine biologist, perhaps you know better. This ocean is a passion of mine though, these matters take up a lot of my energy and mental real estate. I want to believe it will thrive very much, but signs really aren’t positive lately.
Apart from this die out, there are a multitude of other dire situations as well. We’ve extirpated several species, caused numerous salmon population extinctions and collapses, the near extinction of a resident killer whale pod, caused the collapse of multiple species of rockfish - the list goes on.