The Flower Gardens -- A Detailed, Scientific Description
There are colorful gardens in the Gulf... some that may be 15,000 years old. Now, with proper management, these gardens have a chance to survive the increasing impacts of human use.
There are no flowers in these gardens, but there is color. The plants are algae and the floral centerpieces are ancient, multi-hued coral reefs, which, by a sheer twist of nature, sit at the ultimate edge of their existence.
These are the Flower Gardens, the northernmost coral reefs on the continental shelf of North America, and, now, a National Marine Sanctuary. Located more than 100 miles off the coast of Texas and 50 feet below the sea's surface, the East and West Flower Gardens are a pair of underwater coral reefs, 12 miles apart. Aside from some low-diversity reefs on neighboring banks, the coral reefs closest to the Flower Gardens are in the Gulf of Campeche from south of Tampico, Mexico, to the Yucatan continental shelf and in the Dry Tortugas, Florida.
Commercial fishermen probably were the modern discoverers of the Flower Gardens. Fishing is quite good in this area and over other reefs along the shelf break off Texas and Louisiana, and on clear days the reefs can be seen from the surface. Snapper fishermen at the turn of the century found bits of the multi-colored coral as well as colorful plants hung in their fishing gear and, because of these colors, began calling the area the Flower Gardens.
As a marine resource, the reefs serve as a regional reservoir of shallow-water Caribbean reef fishes and invertebrates. They are home to al least 80 speceies of algae, 253 known macroinvertebrate species, and more than 175 fish species. The Gardens are significant habitats for lobster, snapper and grouper. Manta rays, loggerhead turtles and spotted dolphins are also frequent visitors.
The East Flower Garden Bank is a pear-shaped dome approximately 3.1 miles in diameter that rises to within 52 feet of the sea surface. The total area of coral reef at the crest of the bank is about 250 acres. The West Flower Garden Bank is oblong-shaped, roughly 6.8 miles by 5 miles, trending northeast to southwest. The live reef atop the dome occupies a little more than 100 acres, rising to within 66 feet of the surface.
The Banks have probably been forming since the Ice Age, perhaps from 10,000 to 15,000 years. Salt layers were deposited in the Gulf of Mexico 160 to 170 million years ago, when the area was a shallow sea subject to extensive evaportation. As sediments continued to mass on the sea floor, internal pressures caused relatively isolated pockets of the salt layers to shoot up through the sediments and force portions of the bottom of the Gulf upward. The Flower Garden Banks have grown atop two bulges in the sea floor caused by the plug-shaped salt intrusions. The calcium carbonate-generating plants and animals have been so productive that no trace of the deformed bedrock can be found. All has been overgrown and covered by biogenic reefrock and carbonate sand and gravel.
Life on the Banks is divided into distinct zones, with discrete living conditions and assemblages of sea life. The shallowest is the Diploria-Montastrea-Porites Zone, which occupies depths less than 118 feet. This is the high-diversity coral reef, an area most accessible to research and recreational divers. Naturally, corals are the most conspicuous organisms here, and massive corals such as the mountainous star coral, Montastrea annularis, dominate. The vast majority of the 253 species of reef invertebrates and 175 reef fish known from the Flower Gardens are found in this zone. Interestingly, there are no large, shallow-water branching corals, sea fans or sea whips, all of which occur in similar depths on other Gulf of Mexico and Caribbean coral reefs. Large concentrations of the small branching coral, Madracis mirabilis, are found at the edge of the main reef, between 1125 and 144 feet deep (Madracis Zone). Limited areas, peripheral to the high-diversity reef, are almost totally covered by seaweeds, forming a Leafy Algae Zone.
Next in the zone scheme is the somewhat deeper and comparatively low-diversity coral reef, the Stephanocoenia-Millepora Zone. It ranges from 118 to 170 feet. Among the 12 varieties of reef-building corals known in the zone, eight are particularly conspicuous -- the blushing star coral, Stephanocoenia michelini; fire coral, Millepora sp; cavernous star coral, Montastrea cavernosa; large-grooved brain coral, Colpophyllia spp; brain coral, Diploria sp; lettuce coral, Agaricia spp.; large flower coral, Mussa angulosa; and the large fungus coral, Scolymia sp. Crustose coralline algae are the predominant encrusting forms occupying dead coral reefrock.
Little is known about the assemblage of organisms in the zone, but reef fish populations appear less diverse than in the shallower zone. Population densities of the black urchin, Diademia antillarum, which is a significant bioeroder of reefrock, may be similar in both zones. Exceptional numbers of the American thorny oyster, Spondylus americanus, have been seen in the Stephanocoenia-Millepora Zone.
The Algal-Sponge Zone is next on the way down the Bank. It ranges between 151 feet and 269 feet at the East Flower Garden and from 151 feet to 288 feet at the West Bank. Coralline algae, which produce spheroidal nodules as well as crusts on the reefrock and rubble, are the dominant living organisms here. Algal nodules, up to fist size, cover 50 percent to 80 percent of the bottom in places.
Overall, the algae are probably more important to reef formation than corals are on the Banks, simply because of the area covered and the amount of carbonate deposits produced. Only several hundred acres of coral exist, compared to several square miles of deeper, coralline algal-dominated bottom.
A variety of sponge species are abundant in the Algal-Sponge Zone, with the stinging touch-me-not sponge, Neofibularia nolitangere, being the most distinctive. Crusts of this sponge occur on nodules, sand or rock within the zone. Fish and mobile invertebrates are attracted to the sponges, and are often seen swimming or crawling among their chimney-like spires. The small yellowtail reeffish is the most abundant species. Researchers also have seen breeding assemblages of asteroid starfish, sea urchins and sea hares. Less is known of the biota occupying the Algal-Sponge Zone, but its diversity may be as high as on the coral reefs.
From 171 feet to below 295 feet is a transition zone. It is here that white, bedspring-shaped, antipatharian sea whips occur. They mark a zone of transition between organisms that exhibit distinct shallow-water traits and those geared to deepwater. The upper parts of this zone blend with the Algal-Sponge Zone.
The nature of the bottom changes at the edge of the Bank, usually rather abruptly, shifting from algal nodules and crusts to a soft, level bottom of mixed, coarse sand. At some places on the deeper portions of the bank are remnants of an earlier world. This is the home to what are called drowned reefs, where coralline algae do not thrive and reef-building corals are absent. These are the drowned remains of reefs that probably grew during periods of lower sea levels. When the sea level was at its lowest during the last glacial age, about 17,000 years ago, these dead reefs may have been vibrating with life, closer to the surface.
Light penetration, water turbidity, sedimentation and temperature are probably the most important factors controlling the present distribution of reef-building corals and coralline algae. The drowned reefs exist in comparatively turbid water and are generally covered with veneers of fine sediment. The drowned reefs attract a number of fish species, particularly small yellowtail reeffish, red snapper, spanish flag, snowy grouper, bank butterflyfish, scorpionfish, and the roughtongue bass. Crinoids, sea whips, sea fans, sponges and non-reef-building corals are the most prevalent attached organisms.
Another factor making the Flower Gardens unique is an unusual underwater salt lake, fed by a brine seep. The seep is located 233 feet below the surface on the margin of the East Flower Garden Bank. Living conditions for most marine organisms are not good here since the lake's water is highly saline, has high levels of hydrogen sulfide and dissolved hydrocarbon gases (methane, ethane and propane), and no oxygen. The lake has an outflow into a canyon that contains a mixing stream, which dilutes the brine to lower salinity, adds oxygen and diminishes the toxic hydrogen sulfide.
The lake, about 80 feet in diameter, is only 10 inches deep. The canyon begins at the end of the depresssion where the lake sits. There, water from the brine seep flows over a small waterfall and down the canyon, which extends roughly 200 feeet to the edge of the bank.
The dominant organisms in the brine lake are sulfide-oxidizing bacteria that live at the very thin interface that separates the dense brine lake from the normal seawater above. Another interesting feature is a whitish mat, made of bacteria and algae, that covers the floor of the canyon and appears to thrive in the unique environment of the mixing stream, where both oxygen and hydrogen sulfide are present. A specialized community of organisms, called thiobios, are able to live in the sulfide-rich canyon stream and feed directly on the plants and bacteria growing there.
Fish and other animals generally cannot tolerate the sulfide of the canyon brine stream, but some fishes such as angelfish, butterflyfish and cottonwick are able to swim in and out of the brine stream to feed. Large red snappers and groupers often swim very close and even dive into the full-strength brine of the lake.
For centuries the Flower Gardens existed far outside the view and influence of humans, subject only to the threats posed by nature's hurricanes and tropical storms. But today, the Banks are on the path of international shipping lanes and are frequented by other large vessels. The tops of the reefs have been scarred and tumbled in places by dragging anchors and swinging cables and chains. Not only is coral destroyed directly, but this mechanical damage may ultimately cause death through pathological infections of lacerated tissue.
Another area of concern since the early 1970s has been offshore oil and gas operation. The Minerals Management Service (MMS) has never permitted this activity on the hard banks, but exploration and production are allowed just beyond the sanctuary boundaries, with adequate monitoring and effluent disposal procedures.
The Flower Gardens also represent a significant harvest area for commercial fishermen in search of red and vermillion snapper and grouper, and are increasingly used by recreational sport fishermen and divers.
As the impact of human activity began to take a more obvious toll in the mid-1970s, efforts began to include the Flower Gardens in the National Marine Sanctuary Program. The site was first considered in 1979, but was withdrawn from active consideration in 1982. The Flower Gardens were later reconsidered in a process that culminated in designation.
The designation established a 41.7-square nautical mile sanctuary (19.2 square nautical miles at the East Bank and 22.5 square nautical miles at the West Bank). The sanctuary will regulate the following activities --
Mooring buoys are already in place at both Banks. Designed to allow boat operators to tie off their lines so they won't have to drop anchor, the mooring buoys are stainless steel U-bolts drilled into long-dead coral rock. A polypropylene line is attached from the U-bolt to the surface buoys. While the regulations ban anchoring by large tankers and other commerical vessels, the mooring buoys make it possible for recreational dive boats and hook-and-line fishing boats to stop over the Banks without dropping an anchor on the coral.
The Flower Gardens represent a bounty of benefits for a variety of users. Being relatively pristine and isolated in the northern Gulf of Mexico, the Flower Gardens are increasingly an attraction for scuba divers from all over the country. The greatest benefits may yet come from continued scientific research. Many, but not all, of the plants and animals of the reef have been identified to species. Major groups remain to be identified, and much research is needed to understand how this important and unique ecosystem functions and how it should be managed.
This document was taken from a brochure developed by the Texas A&M University Sea Grant College Program in cooperation with the National Marine Sanctuary Program and the Texas State Aquarium.
Text by Amy Broussard and Dr. Thomas J. Bright, Texas A&M University Sea Grant College.
Design by Amy Broussard
Scientific Consultant -- Dr. Stephen Gittings
Texas State Aquarium Coordinaor -- Val Waisanen
Full Panel Photographs (in the original brochure) by Stephan Myers.
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