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Precious Cargo:Shipwrecks as Habitat
By Dave Trubey, CZM's Board of Underwater Archaeological Resources (BUAR)
For many people, the mention of a shipwreck conjures up fanciful images of trunks filled with gold, silver, and precious jewels. In reality, while the vast majority of wrecks contain no such material rewards, they are frequently overflowing with the glittering treasures of another sort—tales of maritime history, places of interest for scuba divers, and habitats that can support a variety of marine life.
With an estimated 2,000 shipwrecks off the Massachusetts coast—ranging in size from small dories to freighters of more than 400 feet in length—wrecks are often full of colorful stories of past lives and times. And, over time, they can develop into colorful homes for a variety of fish, mollusk, and plant species.
What draws particular creatures of the sea to these ruins? This question is a subject of debate and research for many experts within the marine community. Part of the answer, it is believed, lies in the way that the wreck structure itself changes seafloor conditions, in turn attracting a range of marine creatures that would not otherwise seek to make this area their home. With the initial onset of a wreck, an existing seafloor and its inhabitants can be destroyed by the impact alone. If the ship is carrying hazardous materials, or is made from composites inhospitable to existing sea life, marine inhabitants' lives can be significantly degraded. Some immediately, some over time. Once the ship and its contents settle, previously established current and sedimentation patterns are changed, sometimes drastically. Existing marine life can be displaced, and the habitat it depended on can be forever changed.
But once the seafloor settles, in place of the displaced, a new underwater microcosm takes root. On a basic level, shipwrecks, be they fairly intact or a wreck of a wreck, increase in the available surface area where certain species of marine organisms can eat, breathe, and reproduce. Wrecks can also provide a complex interface with the water column (i.e., the area between the seafloor and the ocean surface) where marine plants and animals that require topographic heterogeneity and hardened structure can colonize and thrive.
Another benefit for some species is the way in which shipwrecks can diffuse strong currents and create pockets of calm water where schools of fish can rest and plankton-rich eddies can form. These conditions are particularly desirable for certain types of fishes in their early stages of development as they can congregate and feed without disruption.
In the shallower waters along the New England coast, creatures such as anemones, mussels, and barnacles are quick to colonize and the transformation of a shipwreck into an environment that supports these marine organisms may take less than a season. Given more time, these areas in turn can attract sea life that is drawn to these assemblages, resulting in an environment desirable to these marine organisms and the divers who love them.
Of particular note to divers, the numerous crevices, cracks, and nooks of the ship's wreck provide refuge for smaller fish and other creatures that may be hiding from their predators. A well-placed beam from a diver's light will often reveal the surprised eyes of a finned critter anxiously awaiting the departure of its unexpected guest. In addition to these spectacular views, these sites often make for very productive fishing grounds. For decades, fishermen have recognized the correlation between "hangs" (bottom obstructions, often times shipwrecks, on which fish nets frequently snag) and an abundance of fish, particularly sea bass and cod. For nautical archaeologists, shipwreck researchers, and divers, the locations of these hangs or "hang data" have become a significant tool for locating uncharted wrecks.
To give a brief example, the schooner barge Winsor was located using hang data in 1993. Once discovered, it could be ascertained that this vessel was constructed in 1923 by the Kelley-Spear Company of Bath, Maine, and measured 202.9 feet in length and 38.1 feet across its beam, and drew 16.5 feet of water. Further investigation revealed that, in 1946, while carrying 1,800 tons of coal from New York to Boston, the vessel was lost during a particularly powerful December blizzard. Today, the remains of Winsor rest off Marshfield, Massachusetts, and serve as a remarkable marine habitat for a variety of species including cod, wolfish, goosefish, sea raven, cunners, anemones, and sea urchins.
The Winsor is one of the known wrecks where the habitat benefits have been verified; we suspect countless habitats exist with treasures yet to be discovered. For better or for worse, when it comes to shipwrecks, one species loss can be another's gain.
Carr, Arne. 2004. Formerly of Massachusetts Division of Marine Fisheries, personal communication.
Morris, Paul C. 1984. Schooners and Schooner Barges. Lower Cape Publishing, Orleans, MA.
Mulloy, Tom. 2004. Bassings Cove Maritime Association, personal communication.
New Jersey Division of Fish and Wildlife. 2001. "How Reef Structures Benefit Marine Life," NJ Reef News.