They were also astonished to discover a massive, vertical sinkhole called a blue hole, 75km south of a bank called Grand Turk, that formed when a cave collapsed inwards.
“Imagine taking an ice cream scoop out of the sea-floor. That’s what we saw – a crater about 300m (980ft) wide to 550m (1,800ft) below sea level,” says Bell.
They believe its steep walls could form the deepest blue hole in the Caribbean, rivalling Belize’s famous Great Blue Hole.
Usually nothing lives inside a blue hole, but cameras dropped inside the new discovery show small sponges, a species of urchin called large spatangoid, and diverse fish species.
And 25km (15 miles) north of Anguilla, the researchers followed rumours spread by local fishers who had pulled up pieces of coral while working. The team confirmed there was a 4km (2.5 mile) reef with mosaics of coral growing in sponge “gardens”.
They also found black coral that could be thousands of years old, making them some of the oldest ever recorded.
“It tells us that these environments are really pristine and healthy,” says Bell.