Mussels anchor themselves with glue threads and can starve attackers in them
A marine mussel squeezes a liquid into a groove on its foot that hardens in seawater into tough, elastic threads. Those threads, the beard cooks pull off, hold it on wave-battered rocks, and mussels have been known to tie down invading dog whelks with them until the predators starve.
Mussel is a loose name covering several unrelated bivalve families. Marine mussels of the family Mytilidae mostly cling to rocks between the tides, and a few in the genus Bathymodiolus live by hydrothermal vents on deep ocean ridges. Freshwater pearl mussels belong to a different subclass, and zebra mussels, despite looking and attaching much like marine ones, are grouped with the clams.
The two hinged valves are pulled shut by strong adductor muscles. In pearly mussels the shell has three layers: iridescent nacre inside, chalky prismatic crystals in the middle and a skin-like coat of the protein conchin outside, which shields the shell from acids released by decaying leaves in fresh water. Freshwater species use a large hatchet-shaped foot to haul themselves through sand and silt, while all mussels feed by pumping water across their gills and sieving out plankton. Clumping together on rocks also helps: mussels at the centre lose less water at low tide.
Reproduction differs sharply. Marine larvae drift for three weeks to six months before settling. Freshwater larvae, called glochidia, must hitch a ride on the gills or fins of one particular fish species, where the fish walls them inside a cyst for two to five weeks. Some mothers wave mantle flaps shaped like small prey fish, releasing larvae when a fish strikes.
Farming is big business. China took 40% of the world catch in 2005, Spain leads in Europe, and Prince Edward Island in Canada grows 80% of North America's cultured mussels. New Zealand harvests over 140,000 metric tons of green-lipped mussels a year, worth more than NZ$250 million in 2009.
Source: Mussel
