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Scientists dive among spawning coral

September 1, 1998
Webposted at 3:05 PM EDT

By Environmental News Network staff

Emma Hickerson, a marine biologist at the Flower Gardens Marine Sanctuary, captured this year's spawning on film.
(ENN) -- Imagine going diving on an August night -- or several August nights to be specific -- into an ocean teeming with the eggs and sperm of spawning coral.

That's just what a group of scientists from the Flower Gardens Marine Sanctuary did, and according to the research coordinator at the sanctuary, it's absolutely beautiful. Emma Hickerson, a marine biologist, described some of the male corals as looking like they were smoking. She said the Blushing star coral females release egg bundles that look like champagne bubbles. Other divers have likened the white bloom of sperm and egg to swimming around in an upside down snowstorm.

Flower Gardens scientists believe that the August moon and warmer waters trigger the spawning. They know it happens once a year, usually in two waves, the eighth and tenth night after a full moon. The phenomenon was first observed in the Atlantic (including Gulf of Mexico) by recreational divers at the Flower Gardens in 1990. This year the first big wave of spawning occurred one night earlier than the researchers had calculated, opening the question of what is a day to coral -- do they start their countdown on the night of the full moon or the following morning?

This year some minor spawning had been observed by recreational divers the night before the first big wave. However, on Aug. 14, the divers from the sanctuary witnessed the spawning of at least five different species of star coral, plus one species of brain coral and some Christmas tree worms. All species go off at different times within this four day window, with most of the activity occurring between 9 p.m. and midnight. The night of the second wave, Aug. 17, was a big night for large brain corals.

This type of spawning is called broadcast spawning, and timing is everything. Not only does it happen just once a year, it is synchronized. For example, with the blushing star coral, , the male releases sperm and then 15 to 20 minutes later females release egg bundles (known collectively as gametes). From there they evolve to a planktonic larval stage, which floats with the ocean current for several days, or even months, until they settle onto a suitable surface.. Obviously, gamete survival is extremely low.

The dive itself, which is some 80 feet down, requires powerful coordination. Divers collect eggs using a net, sperm in Ziploc bags. The divers have to be quite sure of the specific coral spawn they're collecting or else it's useless once it reaches the research vessel topside. The samples are placed into a mesh bag which is sent up to the surface by inflating a lift bag, using some of the diver's air supply. This saves divers from going up and down and risking the bends. Once the samples reach the boat, the eggs and sperm of a specific speciare placed into a bucket, creating a "gamete soup". They're sampled every half hour or so to document fertilization and progression of development to the planktonic larval stage.

This gives the researchers a better understanding of the reproduction process of coral, but also will hopefully lead to artificially recruited (settled) coral being available for use as a repair mechanism when coral reefs are damaged by ship groundings, storms or disease.

The divers bring racks that hold quarry tiles that are then covered with mesh nets down to the bottom and inject them with larvae that have formed in the gamete soup in the hope that they will settle onto the tiles, grow and be available for transplanting if needed.
In addition to studying the timing of the spawning and the reproductive process, the scientists and divers placed metal racks on the reef. The racks hold quarry tiles, which provide a good surface for larvae to attach to and grow. The racks are then covered with mesh nets and larvae that have formed in the gamete soup are then injected into the net with the hope that they will settle onto the tiles, grow and be available for transplanting if needed.

The Flower Gardens is probably not fertilizing itself. The larvae from other reefs down current (e.g. Mexico) probably are, so it is important to not only protect coral reefs in our own waters, but promote healthy reef systems worldwide.

Copyright 1998, Environmental News Network, All Rights Reserved

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