what was its influence?
It influenced Robert Louis Stevenson's Treasure Island, William Golding's  Lord of the Flies etc
The Coral Island
Robert Louis Stevenson's 1882 novel "Treasure Island" was in part inspired by "The Coral Island", which he admired for its "better qualities", as was J. M. Barrie's character Peter Pan; both Stevenson and Barrie had been "fervent boy readers" of the novel. Novelist G. A. Henty was also influenced by Ballantyne's audience-friendly method of didactism.

William Golding's 1954 novel "Lord of the Flies" 
what is the coral island? It is a novel. who is the author of this novel? It is written by a Scottish author. what is the historical context behind it? It began a trend in boys' fiction by using boys as the main characters. what genre and style did it follow? Fiction
wiki:10704714
The Coral Island [SEP] Influence
Like the Coral Island". Jack also makes an appearance in "Lord of the Flies" as Jack Merridew, representing the irrational nature of the boys. Indeed, Golding's three central characters – Ralph, Piggy and Jack – are caricatures of Ballantyne's heroes. Despite having enjoyed "The Coral Island" many times as a child, Golding strongly disagreed with the views that it espoused, and in contrast "Lord of the Flies" depicts the English boys as savages themselves, who forget more than they learn, unlike Ballantyne's boys. Golding described the relationship between the two books by saying that "The Coral Island" "rotted to compost" in his mind, and in the compost "a new myth put down roots".