Dynamics ofDreissenaspp. veliger larvae in some Bulgarian reservoirs

Abstract

Two invasive mussels from the genus Dreissena occur in Bulgarian inland waters À Dreissena polymorpha and Dreissena rostriformis bugensis. They are well known invasive species, but there is lack of information about the presence, quantitative parameters and distribution of their larvae. We present the first data that concern the veliger larvae dynamics in Bulgarian inland waters, with several infested reservoirs being studied within the period 2009À2012. The present study was designed to determine their distribution, density and seasonal dynamics. Veliger larvae were found in all of the studied reservoirs. Their abundance was in the range from 166 individuals per cubic meter (ind m ¡3) to 28,400 ind m ¡3 in different seasons and reservoirs. The presence of veliger larvae was detected in the plankton also during the winter: February 2011 (3.7 C) and March 2012 at temperature 7.5 C. The maximum abundance of larvae was found at 26 C. The variation among annual data, which was observed in our study implied that further regular and long-term studies of the early life stages of the Dreissena mussels is required in order to monitor the dynamics of these species in the inland waters of Bulgaria.