Grenvilles Planet - sf68 (Michael Shaara)

Two members of the galactic survey ship Mapping Command, Wisha and Grenville, approach what appears to be a planet entirely covered by ocean, with the curious exception of a single small island.

On the island, they discover distinct and thriving animal life—plants and creatures that, by all scientific reasoning, should not exist given the planet’s harsh tidal conditions.

The explorers are puzzled: how could terrestrial life persevere when enormous tides, hundreds of feet high, would devastate any ecosystem repeatedly? They theorize there must be an underlying anomaly—perhaps the island is protected by an energy field, a concealed moon, or even intelligent intervention.