Cracking Pearlymussel (Hemistena lata)

 

 

Status: Endangered

 

Habitat: This mussel prefers gravel riffles of medium-sized streams, and mud and sand bottoms in slower-moving water. It buries itself in the gravel with only its feeding siphons exposed.

 

Behavior: Reproduction requires a stable, undisturbed habitat and a sufficient population of fish hosts to complete the mussel's larval development. When the male discharges sperm into the current, females downstream siphon in the sperm to fertilize their eggs, which they store in their gill pouches until the larvae hatch. The females then expel the larvae. Those that manage to find a fish host to clamp onto by means of tiny clasping valves, grow into juveniles with shells of their own. At that point they detach from the host fish and settle into the streambed, ready for a long (possibly up to 50 years) life as an adult mussel.

 

Why It's Endangered: Dams and reservoirs have flooded most of this mussel's habitat, reducing its gravel and sand habitat and probably affecting the distribution of its fish hosts. Reservoirs are fatal to most riverine mussels; one researcher counted 45 mussel species in a river before the construction of a dam. Four months after the dam was completed, he could find none. Dams and reservoirs are also barriers that isolate upstream populations from downstream ones.

Erosion caused by strip mining, logging and farming adds silt to many rivers, which can clog the mussel's feeding siphons and even smother it. Other threats include pollution from agricultural and industrial runoff. These chemicals and toxic metals become concentrated in the body tissues of such filter-feeding mussels as the cracking pearly, eventually poisoning it to death.

 

November 1997

 

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