Which organism was introduced to the United States from Southeast Asia and has become a significant pest in almost every river system?

• A. Zebra mussels
• B. Grass carp
• C. Amus pike
• D. Asiatic clam

Answer: (D)

The key idea is how an aquatic species from Southeast Asia can become a widespread pest because it reproduces rapidly and thrives in a wide range of conditions. The Asiatic clam, native to Southeast Asia, was introduced to the United States and has since colonized virtually every river system. Its small, hardy individuals reproduce in huge numbers and its larvae disperse easily with water flow, allowing rapid and broad spread. Once established, dense clam beds outcompete native mussels, alter sediment and nutrient dynamics, and can clog water intakes and irrigation systems. Its ability to survive in varied temperatures, oxygen levels, and flow conditions makes it exceptionally difficult to control, which is why it’s become such a persistent and costly pest in many river ecosystems.