LIGHT, GRAVITY AND CONSPECIFICS AS CUES TO SITE SELECTION AND ATTACHMENT BEHAVIOUR OF JUVENILE AND ADULT DREISSENA POLYMORPHA PALLAS, 1771

Abstract

Dreissena polymorpha, the zebra mussel, is one of the most important components of the aquatic ecosystems it inhabits, due to high densities and filtration rates of this fouling organism. This laboratory study deals with several physical and biological factors influencing zebra mussel juveniles (<10 mm) and adults (>10 mm) site selection behaviour and their byssal attachment to substrate. Mussels preferred black substrate rather than white. This preference was found to be stronger in smaller individuals. Furthermore, all mussels, independently of their size, selected shadowed sites and avoided illuminated ones. Large mussels attached more often in darkness than in light, while for small specimens light conditions made no difference. Large mussels tended to attach to lower parts of vertical test-tubes, while the numbers of small specimens in both halves of the test-tubes were similar. If initial conditions, used by mussels to select their attachment site, were changed by turning the test-tubes upside down, small individuals detached and looked for a new site more frequently than large ones. Large mussels attached more often in higher densities of conspecifics, but physical contacts among conspecifics and their size composition seemed to have no impact on attachment. This study shows that many environmental stimuli influence locomotion and attachment of post-metamorphic zebra mussels. Therefore, the behaviour of this group may impact upon adult distribution observed in field. Preferences exhibited by mussels lead to the creation of dense aggregations in dark, deep places, providing protection against dessication, predators and excessive water flow.