Not to be confused with Coral Island.
The Coral Island contains examples of:
- Abandoned Area: The boys keep finding evidence that a European was here before, such as a tree stump with initials carved into it and an elderly stray cat that Peterkin adopts. Eventually they find a small, run-down hut that's on the verge of collapsing. When they go inside, they find the skeletons of a man and a dog lying together on a bedstead.
- Arranged Marriage: The tribal chief Tararo has betrothed his adopted daughter Avatea to another chief she doesn't love. She wants to marry a different chief, who has converted to Christianity, but Tararo tells her that if she doesn't agree to go to her betrothed to be married, he'll send her to him to be eaten.
- Briar Patching: Attempted by Ralph when pirates arrive on the island. The boys hide out in a cave with an underwater entrance, and when Ralph comes out to see if it's safe, the pirates grab him and interrogate him as to the location of his two friends. Ralph says, "Villain, to blow my brains out would make short work of me, and be soon over. Death by drowning is as sure, and the agony prolonged, yet, I tell you to your face, if you were to toss me over yonder cliff into the sea, I would not tell you where my companions are, and I dare you to try me!" in the hopes that they'll throw him into the ocean and he can swim back to the cave. The pirate captain almost has Ralph thrown into the ocean, but changes his mind at the last minute, and decides to kidnap Ralph and put him to work as The Cabin Boy instead.
- Burial at Sea: Bloody Bill is shot while he and Ralph are fleeing from the pirates' failed raid on the natives. The two make it safely to the ship, but he dies the next day. Ralph ties a cannonball to his legs and drops him overboard.
- Easy Evangelism: The people of the inhabited islands are much more eager to adopt European religious and cultural practices than they usually were in real life. One example comes near the end of the book, when Ralph, Jack, and Peterkin have been captured by angry cannibals and are held prisoner in a cave for a week while they wait to be eaten. Then they're suddenly freed. A missionary arrived while they were imprisoned and converted the whole tribe in days. The boys leave the cave to find the old idols being thrown into a bonfire while thousands of natives cheer. By the time they leave the island, the natives have marked out plots to build European-style houses.
- "Far Side" Island: The lagoon around the island contains a number of tiny islands, some with one or two coconut trees growing on them. The castaways visit some of those islands after they build a boat for themselves.
- Kick the Dog: One of the pirates swings Peterkin's cat around by the tail before tossing it into the ocean. Jack says, "You see what we may expect. The man who will wantonly kill a poor brute for sport will think little of murdering a fellow-creature."
- Nostalgic Narrator: Ralph narrates as an older man who fondly remembers his time on the island.
- Only Known by Their Nickname: Ralph Rover's real last name is never mentioned. "Rover" is a nickname he received when he was apprentice to a coasting vessel because of his love of travel.
- Solar-Powered Magnifying Glass: One of the objects the boys bring from the sinking ship is a spyglass. One lens is broken, but they use the other to light fires.
- Taught by Television: Jack reads a lot of adventure novels, which helps him identify many of the plants and animals on the island.
- Threatening Shark: The castaways paddle into the lagoon on a log to fish, only to find themselves pursued by a shark. They briefly distract it by throwing the fish they've caught at it. Then Jack beats it off with a paddle, upsetting the log and dumping the three of them into the water. By that point they're close enough to swim to shore before the shark gets close to them again, but they never venture into the lagoon again until they've built a proper boat.
