Wood structures are subject to various types of damage in the marine environment, mostly biological.
Organisms collectively referred to as marine borers pose the greatest threat to wood. Once a marine borer has infiltrated an untreated marine piling, for instance, it is only a matter of time before the entire structure will become infested, then 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:
- Teredo navalis, a marine bivalve mollusk, uses the ridged and roughened surfaces of its two shells as tools for boring. Often resembling a worm, Teredo navalis may grow up to two feet long, although its shells (which enclose only the front end of the body) remain only one-half inch long. Like other marine borers, Teredo navalis feeds on wood particles and minute organisms.
- Also a mollusk, Bankia gouldi is a native species first identified from specimens found in Norfolk Harbor in Norfolk, Virginia. Bankia gouldi can survive and even thrive in lower-salinity environments than Teredo navalis, can withstand harsh winter conditions, and are as devastating to marine structures as Teredo navalis.
- Commonly referred to as a “gribble,” Limnoria lignorum causes a tremendous amount of damage. An isopod, Limnoria lignorum is far more conspicuous than many other marine borers.
A traditional method for preventing marine borer infestation was to use creosote-impregnated pilings. However, because of environmental damage, many states now prohibit the use of creosote as well as numerous other pile-treatment chemicals.
Some newer, more environmentally sound chemical treatments are available for new construction, while 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 lives of wooden structures in the marine environment.
Marine borer infestations can be controlled or altogether eliminated, but each situation and location is unique, necessitating a variety of approaches.
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To learn more about potential corrosion solutions, see Countering Corrosion.