Dredging Money From The Bank

What effect aragonite mining actually will have on any parcel of the Great Bahama Bank is still a wild guess since no one has a sufficient grasp of the problem. Aragonite is fairly heavy stuff, weighing almost three times as much as water. When stirred up, the largest granules sink quite rapidly, but in a hundred tons of the deposit there are a couple of tons of very fine stuff that can stay in suspension for a week. In that time a large cloud of such material may travel 30 miles, riding the tide and the whims of the wind, casting shadows over rich marine areas that seldom suffer under such a pall. In scientific papers already published on the Great Bahama Bank there is good information about the movement of water, but none detailed enough to indicate just how a constant stream of cloudy water is apt to wander from a given location.

Before any biologist could assess the effect of aragonite mining, he would have to know a bit about the operation, specifically how the dredges are to be used and the expected rate of production. The Dillingham Corporation has declined to give out such information, maintaining that it might be "a benefit to other suppliers of limestone on the mainland." Since the corporation has exclusive rights to the Bahamian drifts, and will be using mining techniques different from those employed in quarries, it is hard to see how such basic information could possibly benefit rival suppliers on land.

The Dillingham Corporation claims that the Bahamian government has already had "ecological studies" made in the area of Ocean Cay and is having "continuing studies every 90 days." Although this claim is a slight overstatement, it is true that, at the request of the Bahamian Ministry of Agriculture and Fisheries, last December Dr. Durbin Tabb of Miami's Institute of Marine Science did make a two-day survey of the area. Dr. Tabb was obliged to conduct his investigation on a budget of $1,500 and without a complete idea of the dredging technique or any knowledge of the expected rate or continuity of production. On the basis of his hit-and-run survey, Dr. Tabb concluded that there was no solid reason why the relatively sterile aragonite drifts should not be mined, provided the operation was kept under surveillance. He was particularly concerned with the effect the altered bottom contour might have on turtle-grass beds in the shallows and what effect the silt from dredging might have on tuna migration in the deep.

Confronted by concern among biospecialists and by rumbling in the press, last month the Bahamian Government Information Services put out their first news release on the aragonite operation. The release emphasized Dr. Tabb's solid opinion that the aragonite areas are undersea Saharas of little biological worth. It said nothing about what might happen when the dust of these submerged Saharas is kicked up by a dredge and drifts over richer areas downstream.

A large hydraulic dredge with a two-foot throat can easily pick up 10,000 cubic yards of loose aragonite in a day. In the process it also sucks up at least six times as much water—roughly 10 million gallons. When that much silty slurry drains directly back into the sea, it creates quite a cloud—virtually an endless stream since dredges usually operate day and night in the interests of economy. Under their contract with the Bahamas, the Dillingham Corporation has the right to pile up 12 artificial islands. Logically, in the coming years the corporation will situate these islands so that dredges with a practical range of several miles can discharge aragonite and slurry directly onto them. In such case the cloudiness will certainly be diminished. The extent of it will depend largely on how much silt the head of the dredge stirs up and how much remains in solution when the slurry drains, or is pumped, off the islands.

When a storm of gale force sweeps the Bahamas it produces cloudy water that may persist over vast areas for as long as a week. A hundred dredges toiling around the clock could not possibly create a condition comparable to what the Bahamas get when a hurricane gives them a good dusting. But there is a difference. The storms of nature are a very sporadic blight. They have occurred throughout many yesterdays and will come again tomorrow. The life of the sea, often hanging in fine balance, has accommodated to that inevitability. Human pollution is a brand-new burden. The unnatural filth suddenly contributed by man may be only a pennyweight of the total, but that is sometimes enough to tip the scale.

Drab though it is to the naked eye, a mat of turtle grass on the sea floor is quite a vital place. On the slimy blades of grass there are a host of minor organisms that feed on smaller organisms and are themselves eaten by larger ones. Seven years ago Dr. Donald Moore of Miami's Institute of Marine Science found, among other things, 28,000 univalve and bivalve mollusks in one square meter of turtle grass. Ten years ago, using seines and push nets, Victor Springer and Andrew McErlean of the Florida State Board of Conservation sampled a shoreline flat of the Florida Keys one day each month for a year. Although the sand and grass tract they searched was less than two football fields in area—and the water did not exceed five feet in depth—Springer and McErlean found 106 species of fish. Grunts, snappers, gobies, porgies, blennies, wrasse, groupers, barracuda; yellowtail and tripletail; batfish and lizard fish; goatfish and parrot fish; big-eyed jacks and little queen triggers; pipefish and filefish and spadefish; bonefish and surgeonfish; needlefish and thread herring—you name it, Springer and McErlean found it. A good number of fish they netted in the shallows were juveniles of species that subsequently take up residence on coral reefs in deeper water.

Many fish that dwell in, on, or around living coral return to the grasses behind the reef to forage. Some of these reef dwellers go to the grass to feed by daylight, others hole up by day and feed at night. As Dr. Gilbert Voss of the Institute of Marine Science puts it, "toward evening, between the reef and the turtle grass, there can be a real traffic jam." While serving at the University of Puerto Rico three years ago, Dr. Jack Randall examined the stomachs of 5,526 reef fish of 212 species. Curiously, although soft coral polyps are easily ingested, and should be nourishing, only 10 of the 212 species that Randall examined had eaten any coral—none of them more than a trace. A preponderance of the species Randall studied were directly or indirectly dependent on the turtle-grass beds for nourishment. Sea urchins, which eat turtle grass, would seem to be too painful a mouthful for almost any fish, yet Randall found a considerable percentage of urchins in the stomachs of 34 reef species.

In the clear waters of the Bahamas today nursery and feeding grounds of turtle grass commonly prosper 25 feet down and have been found at 40 feet. By contrast, for want of light in the turbid waters of Biscayne Bay around Miami; turtle grass is no longer found much deeper than 10 feet. To sum it up, when a dredge forces a turtle-grass bed out of business, the curtain also comes down on a hell of a big variety show.

It is a common fallacy of man to believe that a profusion of other forms of life is proof of their prosperity and permanence. Despite all its variety and oddity, despite its apparent extravagance and luxuriance, a coral reef is often a desperate place. As viewed through a diver's mask, magnified to heroic proportion, the finest reefs of the Bahamas seem to be durable, monumental works of long standing. In truth the very best of Bahamian reefery is no more than a thin veneer—a very recent culture of reef corals that has managed to take hold and spread mostly in the past 5,000 years under conditions that have probably never been ideal.