Dreissena

Content sourced from Wikipedia, licensed under CC BY-SA 3.0.

Dreissena is a genus of small freshwater mussels in the family Dreissenidae. They attach to firm surfaces with threadlike structures called byssal threads and are unusual among freshwater bivalves because they can reach high densities on hard substrates while still having a planktonic larval stage. They are widely known as one of the world’s most aggressive freshwater invaders because they spread at every stage of their life cycle.

Description and range
Dreissena shells show dark and light bands on a light-tan shell, with a triangular shape and sharp points near the hinge. They are native to the Black Sea, Caspian Sea, and Azov Sea region (originally found in Ukraine and southeast Russia) but have spread worldwide through ballast water and hull fouling, including the Great Lakes in North America.

Habitat
They prefer large estuaries, rivers, and lakes with firm surfaces to cling to. They are usually bottom-dwellers, but their larvae float in the water, so they can travel with currents. Water bodies with moderate minerals and a higher pH are common homes for them.

Life cycle and reproduction
- Males fertilize eggs released by females in autumn; fertilization occurs outside the body.
- Eggs are released in spring as water warms; spawning starts around 12°C, with peak egg release around 17–18°C.
- Optimal larval development occurs at 20–22°C.
- A single reproductive cycle can produce tens of thousands of eggs; eggs and larvae disperse with currents and winds.
- After hatching, young mussels settle by attaching to a substrate with byssal threads. If they don’t find a sturdy surface, mortality is extremely high (up to about 99%).

Growth and feeding
- Lifespan is about 3–9 years. They grow roughly 0.5 mm per day, or about 1.5–2 cm per year.
- Dreissena are filter feeders, drawing in water and filtering out algae and some microzooplankton. They can filter about a liter of water per day.
- They use inhalant and exhalant siphons to take in and expel water.

Impact and spread
- They can clog water intake pipes in power plants and water treatment facilities (biofouling) and add drag to boats.
- They outcompete native species for food, altering local ecosystems.
- Their ability to move and settle at every life stage helps them invade new areas and establish widespread populations.

Note
The Dreissena genus includes several living species, all sharing these key characteristics.