Estimate zebra mussel veliger density from the riverbanks, lotic stretch and reservoir, in two Mediterranean rivers (E Spain)

Larval detection is the most commonly used procedure for monitoring the presence of Zebra mussel, Dreissena polymorha. Different filtering techniques carried out on the banks of the Ebro (EB) and Júcar (JU) rivers (Eastern Spain) in different water conditions are compared. Low volume water filtration from the banks is a method sensitive enough to detect variations in larval density due to water temperature and flow rates. The EB densities were lower and related to the temperature of the water. In JU, different spawning strategies and a much extended period of larval releasing into the water occurred in two consecutive years. The presence of larvae in both rivers was constant for many months of the year, during which various reproductive cycles occurred, facilitated by high water temperatures during mid-spring to late fall. Shoreline surveys can be easily used for allowing the early warning of the presence of this dangerous invasive species, mitigating damages and preventing its spread into new areas. However, it is important to choose a suitable location for capturing the larvae on the banks of reservoirs and in flowing rivers.