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The Evolution of a Shipwreck




A barracuda cruises past the wheelhouse of the USS Spiegel Grove.

What happens when 9,000 tons of steel hit a sandy bottom less than a mile from a coral reef in the nation's preeminent marine sanctuary? There's a high probability of a world-class dive site, which will enhance tourism. But what about all the fish and invertebrates that make the wreck their home? Where do they come from? Does the wreck alter the concentration of native marine life on nearby natural reefs? Are the fish on a wreck congregated and therefore easier to catch? Important questions such as these are central to any discussion of the liabilities and benefits of artificial reefs.

In 2002 the USS Spiegel Grove was placed on the seafloor of the Florida Keys National Marine Sanctuary about 6 miles east of Key Largo, becoming (at the time) the world's largest intentionally sunk artificial reef. Sitting in 130 feet of water, the 510-foot-long ship is now a mecca for wreck divers the world over. The wreck rested on its starboard side for three years before it was fully righted by storm surge during Hurricane Dennis. This was the blank slate that Reef Environmental Education Foundation (REEF) had to work with when it was commissioned to survey the recruitment of life onto the wreck. REEF's surveys began prior to the sinking to establish a baseline of life on the sandy seafloor and along nearby reefs. REEF continued monitoring the Spiegel Grove for five years after it was sunk.

Unsurprisingly to wreck-diving enthusiasts the Spiegel Grove now hosts an incredible diversity of marine life. More than 144 species of fish have been documented on the wreck including commonly seen bluehead wrasses, bar jacks and great barracudas, as well as more rarely spotted longlure frogfish and unicorn filefish. Federally protected goliath grouper and large cubera snapper are becoming ever more common.


The French angelfish is one of many species of reef tropicals that makes its home on the massive shipwreck.

REEF was also tasked with determining how native fish assemblages on nearby natural reefs respond to such a massive structure being situated just a few hundred yards away. Previous studies on smaller artificial structures demonstrated that such structures may aggregate fish from surrounding areas. This is significant in terms of marine-life management, for if fish are spread out in low densities over a large area they may be harder to catch. Consolidated on a wreck, however, they may be easier to catch and thus be lost in greater numbers. While marine life in the Upper Keys has been protected from spearing for decades, hook-and-line angling is permitted on this wreck, and therefore fish are vulnerable. Yet REEF data suggests that the Spiegel Grove actually provides a net increase in fish abundance without significant migration away from nearby natural reefs.

One reason for the increase may be the sheer size and complexity of the wreck, which provides habitat that may be more hospitable for some species than the surrounding natural reef. Another unintended consequence working in favor of abundant marine life may be the fact that so many divers use the wreck that it's difficult for fishermen to find an open space to drop a line. With eight mooring buoys running the length of the wreck and estimates of tens of thousands of divers visiting the site each year, its sheer popularity may be establishing it as a de facto marine protected area.

Key Largo is no stranger to ships as artificial reefs. Since the time of the Spanish exploration, countless ships have grounded and sunk in the Florida Keys. More recently, in 1987 the U.S. Coast Guard cutters Bibb and Duane were intentionally placed as dive sites. The Duane, which sits upright like the Spiegel Grove, has been down for nearly 30 years, and the World War II casualty Benwood has been down since 1942. Each hosts large schools of fish, diverse macro life and colorful sponges. The assemblages of marine life at these wrecks are much more complex and mature than the 11-year-old assemblage on the Spiegel Grove. But the currents sweeping the Spiegel Grove have brought about rapid colonization of algae, sponges, corals and gorgonians. The chain of life is already well established on this reef of steel.
Learn More
For more information on the fish found on the Spiegel Grove, visit www.reef.org/db/reports/geo/TWA/34030038/ or view the five-year report.


© Alert Diver — Fall 2013