Wood in the Marine Environment
Wood structures are subject to other types of damage in the marine environment, mostly biological.
The Problem of Marine Borers
Of greatest concern are organisms collectively referred to as marine borers. Once a marine borer has infiltrated an untreated marine piling, it is only a matter of time before the entire structure will become infested, weaken, and collapse.
Although hundreds of species of marine borers exist, three are quite common in the northeastern United States: Teredo navalis, Bankia gouldi, and Limnoria lignorum.
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Teredo Navalis
Teredo navalis is a marine bivalve mollusk. Its two shells, enclosing only the front end of the body, function as a tool – their ridged and roughened surfaces are used for boring.
These borers often resemble a worm and may grow up to 2 feet long, although its shells remain only 1/2 inch long. Like other marine borers, Teredo navalis feeds on wood particles and minute organisms.
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Bankia Gouldi
Also a mollusk, Bankia gouldi is a native species and was first identified from specimens found in Norfolk Harbor in Norfolk, Virginia. Bankia gouldi can survive and even thrive in salinity far lower than those tolerated by Teredo navalis, can withstand harsh winter conditions and are just as devastating to marine structures.
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Limnoria Lignorum
Limnoria lignorum, commonly referred to as a “gribble,” causes a tremendous amount of damage and is far more conspicuous than many other marine borers. Limnoria lignorum differs from Teredo navalis and Bankia gouldi, however, in that it is an isopod, not a mollusk.
According to recent estimates, Teredo navalis alone is responsible for over $200 million dollars in annual damages to wooden structures in the United States, while annual damage in the United States from all species of marine borers reaches into the billions of dollars.
What Can Be Done to Prevent Marine Borer Damage?
One traditional method to prevent marine borer infestation was to use creosote-impregnated pilings. However, in this era of greater environmental consciousness, many states have prohibited the use of creosote as well as numerous other pile-treatment chemicals.
Some newer, environmentally sound chemical treatments are available for new construction, and for older installations a variety of wraps or encapsulations exist. Even in the case of new construction, serious consideration should be given to an appropriate wrap or encapsulation process to extend the life of the structure.
Marine borer infestations can be controlled or altogether eliminated, but each situation and location is unique, necessitating a variety of approaches.
