Creatures of the Underwater Caves

Blue Holes
Beneath the land surface of the Bahamas, the underwater caves known as blue holes stretch for hundreds of miles in all directions. Today, these labyrinthine passages host a variety of tiny sea creatures found nowhere else on the planet. But during the last ice age when sea levels were much lower, the caves were the high-and-dry habitat for a completely different group of animals.

An Owl's Roost
On one dive into a blue hole on Great Abaco Island in the Bahamas, scientists uncovered what appears to be an ancient owl's roost. This roost likely dates back to more than 12,000 years ago, when the sea level was as much as 130 meters (427 feet) below modern levels. By the time the scientists finished picking through all the bones uncovered at the perch—presumably the remains of the owl's prey—they had identified 46 animal species, many of which are now locally or globally extinct.

Abaco Flightless Rail
Scientists recognized some bones from the roost as the remains of a new species of flightless rail. Rails have slender bills and long legs that help them navigate through water-logged vegetation. Today, other flightless members of this family, like the Aldabra rail shown here, still live on oceanic islands where they evolved in the absence of predators and had no need to fly.

Haitian Boa
The Haitian boa (Epicrates striatus) feeds on small lizards, mammals, and birds, and can grow up to 2.6 meters (8.5 feet) in length. Unlike many of the other species of animal found in the remains of the owl's roost, this boa species still lives on the island.

Cave Swallow
The cave swallow (Petrochelidon fulva) is a small, stocky songbird that builds its nest in the so-called twilight zone of caves—right at the entrance, where the light levels are low. The species still lives on some islands in the Bahamas, but not on the island where these bones turned up.

Eastern Meadowlark
The eastern meadowlark (Sturnella magna) doesn't live on Abaco anymore, but it's still present in other parts of the Americas. The species constructs nests in patches of thick, grassland vegetation where it forages for insects and grain. Despite the name, the meadowlark isn't actually a lark—it belongs to a different taxonomic family that includes blackbirds and orioles.

New Species
By around 7,000 years ago, the polar ice caps melted to about their modern-day size and the sea level rose accordingly, flooding the blue hole caves in the Bahamas and elsewhere with saltwater. Marine biologist Tom Iliffe is pictured here with a new species of invertebrate. Most of the species discovered in the deep, oxygen-depleted marine waters are new to science, so we know relatively little about them.

Speonebalia cannoni
Discovered: 1995
Location: Bahamas, Caicos Islands
Size: 8-11 mm
Like many of the animals from these lightless caves, this small shrimp-like crustacean lacks eyes and pigment. Both would be useless in the totally dark underwater environment. S. cannoni was first observed in the Caicos Islands but has since turned up in Bahamian caves.

Parhippolyte sterreri
Discovered: 1981
Location: Aldabra, Bahamas, Bermuda, Fiji, Funafuti Atoll, Hawaii, Loyalty Islands, Mexico, Molluca Islands, Philippines
Size: 30.7 mm
This bright red shrimp is one of the larger species that lives in blue holes. The species is recognized, in part, by the white spots on each of its joints and its tail. P. sterreri was first observed during a dive into an inland blue hole in Bermuda, but it has since been found in offshore submarine caves in the Bahamas and elsewhere.

Speleonectes kakuki
Discovered: 2009
Location: Andros and Cat Islands, Bahamas
Size: 18-26.5 mm
This species is named for Brian Kakuk, a diver and guide who helps scientists venture into the dangerous underwater world of blue holes in search of new animals. S. kakuki belongs to the crustacean class Remipedia, which was first discovered in 1981. There are 12 other known species in the genus Speleonectes—a word that literally means "cave swimmer."

Pelagomacellicephala iliffei
Discovered: 1985
Location: Caicos Islands
Size: 5-9 mm
This segmented worm was first sighted in a deep tidal pool within a blue hole. The species was named for biologist Tom Iliffe, who has found more than 300 new invertebrate species in blue holes. These animals represent three new orders, nine new families, and 55 new genera. Given that blue holes are still relatively unexplored, many other animals unknown to science likely lurk in their depths.