KINGSTON, R.I. -- February 27, 2001 -- The blue mussel clings to life by a thread. Make that about 80 byssal threads in the winter and 30 or so threads in the summer, but you get the idea that life for these hard-shelled mollusks is quite dramatic.
If hanging on to a rock in the intertidal zone while waves come and go isn’t enough, the blue mussel faces the threat of being ripped off its rocky perch by violent storms or hurricanes.And now comes global warming, which is making the world windier and the waves stronger. The mollusk will either have to get stronger by producing more threads or fall off and die.
Will the blue mussel whose species is dominant throughout the world maintain enough muscle – actually extra cellular fibers -- to remain steadfast or simply go with the flow?
That in a seashell is something University of Rhode Island assistant professor Emily Carrington of Wakefield, an expert on the blue mussel and its marine community, is trying to determine.
Funded by a three-year, $320,000 National Science Foundation grant, Carrington’s overall research goal is to determine the ability of mussels to adjust their attachment strength to prevailing wave conditions so that she can predict when mussels may be dislodged based on changes in wave activity.
Since 1998, the URI biologist in the College of Arts and Sciences has monitored blue mussels living at the edge of Narragansett Bay, measuring their size and strength each month.
Back in her URI lab, Carrington uses a materials testing machine, commonly used by engineers to test materials such as concrete, to measure the strength and elasticity of the mussels’ threads. She is also examining the force required to crush its shell.
Just how far can the threads stretch? "The threads are nature’s little bungy chords," says Carrington, noting that the threads are stronger than most rubber materials and can stretch up to twice their length before breaking. That function is important because as tethers, only the threads that are in tension can bear the load of a crashing wave. Threads with excess slack are useless. The ability of the threads to stretch allows additional threads to be recruited to hold on.
An adult mussel is about 2 inches long. (The threads are about half the length of the shell). The mussel’s small size is perfect for the challenges it faces. Consider the force of a large breaking wave. Translated into wind speed, it’s like a person standing on the wing of an airplane going 600 m.p.h. and trying to hang on. Obviously, humans wouldn’t fare very well on wave-swept rocky coasts, but the diminutive mussel, resembling a rivet on the airplane wing, is quite able to keep its composure. "There are no intertidal redwoods," comments Carrington.
The mussel is twice as strong in the winter as in the summer. In fact, its holding power is weakest in September making them vulnerable to hurricanes. "It appears that the blue mussel responds well to the predictable, but doesn’t fare well with the unpredictable," says the URI professor.
The reason for its weakness may be that the mussel is on the ropes at the end of the summer. The mussel uses nearly all its energy and resources trying to reproduce during the spring and summer. It isn’t easy. Their offspring are hardly conceived in a conventional fashion. Both male and female mussel continually secrete eggs and sperm (called gamete) hoping the two will meet in the water column and become one larva. The larva spends about six weeks in the water before making its way back to shore to seek a rock, metamorphose, and cling.
"The ocean is a rich soup of plankton," says Carrington. "Being a filter feeder, the blue mussel sucks in the water and may actually help clean the ocean."
Carrington believes that the mussel is everything it’s cracked up to be. "My research will help us understand how stable mussel populations are in the face of increasing storms so that it can continue to keep the water clean and be enjoyed by diners."
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