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Dive Dry with Dr. Bill

#527: A Blue Hole

During the winter of 2005 I spent two months in Belize and Honduras, working on a Lindblad Expeditions eco-cruise ship as their marine biologist and underwater videographer. On our cruises between Belize City and the island of Utila off Honduras, we made many stops at Lighthouse Reef, an atoll about 40 miles off the coast of Belize. This atoll is the location of the Great Blue Hole, made famous by my childhood idol Jacques Yves Cousteau for whom I worked briefly in 1985.

The Great Blue Hole is a circular depression 984 feet in diameter in the limestone reef. Measuring 407 ft. deep, it is well beyond my abilities (or desire!) on open circuit SCUBA gear. Despite doing many spectacular dives on Lighthouse Reef, the ship could not spare a Zodiac to get us to the Great Blue Hole a few miles away. They were understandably needed to transport our paying passengers to and from the beach. So after two months I left Belize without ever even seeing this spectacular sight.

Recently, on my trip to the Bahamas I was able to experience another Blue Hole near Nassau on my last dive with Blackbeard's. As a marine biologist, I must say it was not my favorite dive... but I'm sure marine geologists are green (or blue?) with envy since these features are truly interesting for submarine rock hounds.

Blue holes are essentially vertical caves that formed during past geologic time when sea level was much lower. Ice age glaciation ending about 10,000 years ago caused much of this drop in water level. Like in other caves, stalactites are often present and may be seen at different depths corresponding to changes in sea level over time. The best examples of blue holes are in Belize, the Bahamas, Guam, Australia and the Red Sea. They got their name because the deep centers of the holes appear dark blue compared to the much lighter blue-green color of the shallower water surrounding them.

The well-contained deep water in blue holes has poor circulation and little contact with the surface water layer. The great depth also limits plant or algal growth in them. Therefore the water in them is often anoxic (oxygen poor) and a great place for bacteria to prosper. This does not make them suitable habitats for the critters I like to film, and I'd need a microscope to record the marine bacteria (which I'm sure would thrill my viewers no end). My filming in the Blue Hole was pretty much limited to the surrounding reef at the top and the few interesting critters I observed to a depth of about 110 ft. on my dive.

In the divemaster's briefing before the dive she mentioned a small cave at a depth of about 70 ft so I went in search of that. When I found it, I discovered it was pretty shallow but filmed it anyway. When I finished, I looked over at where my left hand rested near the entrance and discovered a spotted moray that must be guarding the cave. That gave me a good opportunity to film one up close and personal. I also found a few lionfish which imaged quite nicely in the light of my video rig.

After a short excursion into the hole itself, I returned to the reef above and filmed there for the rest of the dive. I wanted to get a few overview segments to show the hole opening as well as record some of the marine life I saw up in the shallows. My buddies Anabel and Dennis soon joined me. Critters up on top included the blue parrotfish feeding in the sand, angelfish, butterflyfish and the only corkscrew anemone I saw during my entire trip.

We ended the dive by trying to figure out which direction the ship was located in. I must admit my aging eyes had no clue, although we could easily have surfaced and swum over to it. But dive buddy Anabel is a pilot for Air France and even without the navigational electronics of her airplane cockpit, she sensed the right direction. Along with Dennis we swam over the Blue Hole to the other side and exited the water, ready to head back to port in Nassau to end our wonderful Blackbeard's adventure.

© 2013 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 29, 10:00 AM weekdays and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. You can also watch these episodes in iPod format on YouTube through my channel there (drbillbushing). Please help me climb out of self-imposed poverty... buy my DVD's (see this link). Yes, take Dr. Bill home with you... we'll both be glad you did!

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Diver peering into the abyss of the Blue Hole, on the edge; moray guarding the cave and oops, I almost slipped.

This document maintained by Dr. Bill Bushing.
Material and images © 2013 Star Thrower Educational Multimedia