MONTEREY, Calif. (AP) — Scientists exploring the sea floor off the coast of central California for deep-water coral and sponges instead found an unprecedented sight: Hundreds of octopuses tucked between rocks with their tentacles inverted and covering groups of white eggs — a posture that is common among brooding females.

The cluster of more than 1,000 gray octopuses latching on to clean, dark rock was found last week in the Davidson Seamount, an underwater extinct volcano in the Monterey Bay National Marine Sanctuary, Chad King, a marine biologist at the sanctuary, said Tuesday.

A submersible...