Biology of the exotic zebra mussel, Dreissena polymorpha, in relation to native bivalves and its potential impact in Lake St. Clair

Abstract

The zebra mussel, Dreissena polymorpha, is a new exotic species that was introduced into the Great Lakes as early as the fall of 1985 . It differs markedly from native species of bivalves in its : (i) shell form ; (ii) mode of life ; (iii) reproductive potential ; (iv) larval life cycle ; (v) population dynamics ; (vi) distribu- tion, (vii) dispersal mechanisms ; (viii) physiology ; (ix) potential impact on the ecosystem; and (x) impact on society and the economy . In body form, it has an anterior umbone, a flat ventral surface with permanent aperature for the byssal apparatus and a shape that together make the animal well adapted for life on a hard surface . The shell has a zebra-stripe pattern, a heteromyarian muscle condition and lacks hinge teeth which make it easily identifiable from native bivalves . The zebra mussel is strongly byssate and has an epifaunal mode of life not seen in native bivalves . The species is dioecious and has external fertilization, the eggs developing into pelagic veligers which remains planktonic for approximately 4 weeks . Gametogenesis begins in late winter to early spring, veligers appear in the water column in late May to early June and disappear in mid to late October in Lake St . Clair. Adults live for about 2 years and have very rapid growth rates. Maximum shell lengths average 2 .3 to 2 .5 cm. Standing crops as high as 200 000 m-2 are present in the 1-m depths of the Ontario shores . Infestations may be interfering with the normal metabolism of native unionid clams and there is potential of the unionid clam populations being reduced or even eliminated from Lake St . Clair.