Andre Norton had a mediocre book about octupi leading an overthrow of humans - Sea Seige. Here is a review with a pretty good synopsis of the plot:
There was nothing left for man—no hole in which to hide
Sea Siege — Andre Norton
1957’s Sea Siege begins as though Norton might be trying to emulate Willard Price’s Adventure novels. A little later, I was reminded of John Wyndham. It might be that Norton was looking at what was selling in the 1950s and shaping her books accordingly.
Like Price’s equally fictional Hunt brothers, Griffith Gunston is the son of a prominent naturalist. (Griffith’s father, Dr. Ramsay Gunston, is an ichthyologist.) Unlike the Hunt brothers, Griffith is not at all interested in his father’s research. Griffith yearns for a career as a jet pilot! That is, if impending nuclear war holds off long enough for Griffith to join the air force.
Unfortunately for Griffith and everyone else on the isolated island of San Isadore, while Griffith may have no interest in what’s under the sea, what’s under the sea has a keen interest in the humans of this part of the West Indies and perhaps humans across the world as well.
As the book opens, a mysterious Red Plague is killing off the fish in the world’s oceans. Given that fishing is a primary activity on San Isadore, that would be bad enough, but the locals are even more concerned by the way ships are vanishing or turning up bereft of crew. While some of the locals blame dupees, sea monsters, a reasonable person like Griffith disagrees. The explanation is a lot more likely to involve enemy submarines, given that the Cold War is accelerating toward Hot. Well, reasonable people can be wrong.
http://jamesdavisnicoll.com/review/there-was-nothing-left-for-man-no-hole-in-which-to-hide
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