Bookmark Us


Reproduction and larval development. Dreissena is of separate sex, usually with a ratio 1:1. Individuals mature at age 0.5-2 years and shell length over 8 mm. A mature female may produce up to one million eggs per year. The fertilization is external in the water column. Spawning of zebra mussel begins when the water temperature is above 12oC and peaks at 15-17oC. The spawning may take place over a period of 2-8 months. The larval life cycle of Dreissena usually takes about 4 weeks. Three stages are recognized: a veliger stage, a post-veliger stage and a settling stage. The veliger larva is free-swimming and possesses a velum - ciliate swimming and feeding organelle. With the loss of the velum and development of the foot the larvae enter the post-veliger stage (pediveliger larva). The foot is used for swimming near the bottom and for crawling. When the pediveliger encounters an appropriate surface, it secretes a byssal thread and undergoes metamorphosis including development of the gills, secretion of adult shell, growth of the foot and mouth, and becomes a juvenile. Additionally, the larvae need suitable bottom substrate to settle and they are sensitive to turbulence. Preferred substrates for settlement are aquatic plants, shells of adult Dreissena and Unionids as well as stones. The preferred depths for settlement are between 0.5 and 4.5 m..



D. bugensis, Ogosta Reservoir

D. presbensis, Ohrid Lake

Photos: Lubomir Andreev


Feeding. Adult Dreissena feed through filtration of water with the help of the gills. Solid particles, including food, are sorted by the cilia of the gills: digestible fine food particles are directed by the cilia towards the mouth for ingestion; while coarse particles are wrapped in mucous that is secreted by cells in the gills and are then expelled as pseudofeces. Adult zebra mussels filter a wide range of size particles, but select only algae and zooplankton between 15 and 400 microns. Dreissena larvae feed with the help of the velum on bacteria, small green algae and blue-green algae of 1-4 μm in diameter.



D. polymorpha, Stoikovtsi Reservoir


D. polymorpha, Lake Hechtsee, Austria

Photos: L.  FÜREDER


Byssal apparatus. On the ventral side, the body of Dreissena forms a muscular foot which provides the means for crawling as well as housing the byssal gland that is responsible for the secretion of byssal threads. Secretions by the byssal gland are passed to a byssal canal which directs the fluid to the base of the foot. The individual byssal threads branch from a central stem, each thread terminating in an adhesive disc. With the help of the byssal threads adult Dreissena can attach to almost any surface and can survive in water velocities of 1-2 m/s. Under unfavorable conditions, adult mussels have the ability to detach voluntarily and to move around the substrate to seek alternate locations. This happens by the secretions of enzymes which cause the release of the byssal threads. The mussel then secretes new threads.


Specimen from Shabla Lake


Specimen from Veleka River
D. presbensis, Ohrid Lake
Photos: Lubomir Andreev


Dispersal Mechanisms. During the pelagic state veligers and post-veligers are transported by currents. Secondary dispersal occurs by the drifting of post-larvae and young adults using the byssal threads.


This website is developed with support from the Bulgarian Science Fund, Ministry of Education, Youth and Science,
within the Project "Assessment and Management of Dreissena spp. Invasions in the Bulgarian Water Bodies",
Contract Number: DO-02-283/2008.

Tyxo.bg  counter