system
Given the following post, respond as if you're commenting on Reddit:
human
[Life] Humans are very good at killing other species. Killing an alien in a space station with no weapons is one thing. Doing it on Earth is another. Is mankind doomed or is fighting off Calvin and its soon to be numerous descendants possible?

Calvin is very obviously hostile but does not seem to kill all life on sight, it didn't kill that final astronaut when trapped with him in the pod?  Would Calvin destroy the entire biosphere?
gpt
While humans have caused many species to go extinct, it is mostly through over-hunting and habitat destruction.  Calvin doesn’t seem to be dependent on any particular habitat and it is better at hunting us than we are at hunting it.

With most of these rapidly growing organisms your best bet is to respond quickly and thoroughly eliminate every trace.  A warning was sent out, so maybe a response can be prepared in time.  The entire crew of the ISS was lost, so presumably people in charge will be taking this seriously.

What concerns me is that it can grow from a single cell to an animate people devouring organism in a matter of hours.  It already has access to the fishermen and whatever they have caught to grow.

I think it comes down to whether the creature can divide.  If it remains one entity then the larger it gets the easier it will be to locate and contain.  If it can spread spores or something though, there might not be any way to contain them all before they can spread over the Earth.  It could just spread pieces of itself around the ocean floor and just slowly grow and spread more until it is far too large to stop.