Population Dynamics, Production And Resource Allocation In The Zebra Mussel, Dreissena Polymorpha, From The Lower Great Lakes, Canada

Five populations of Dreissena polymorpha from three lakes (Lake St. Clair, Lake Erie and Lake Ontario) were examined to determine the population dynamics, reproductive cycle, secondary production and the allocation of resources to somatic tissue and shell, and gamete production.;Variation in life history characteristics, such as lifespan, age at first reproduction, maximum size and fecundity were observed both within and among sites, although the among-site variation was greater. The lifespan of D. polymorpha ranged from 2 to {dollar}\u3e{dollar}4 years depending on the lake. The onset of sexual maturity was related to size, not age. Individuals became sexually mature between 7 and 10 mm in shell length, which corresponded to 1 to 3 years of age.;Water temperature and seston concentration were the primary factors regulating the reproductive cycle of D. polymorpha populations in this study. Gametogenesis began at temperatures below 10{dollar}\sp\circ{dollar}C, although no maturation of oocytes occurred until water temperatures exceeded 12{dollar}\sp\circ{dollar}C. Spawning in all populations was initiated by a peak in seston concentration. Spawning generally consisted of the successive maturation and proliferation to two oocyte cohorts which were present in the gonads of females at the beginning of the spawning season. However, in years in which there were low seston concentrations and/or high temperatures, only one cohort was released. The second oocyte cohort was reabsorbed to enable maturation of the first.;There was considerable temporal and spatial variation in secondary production at both the population and individual level. Differences in population production were correlated with population density, whereas variation in individual production was attributed to temperature, food supply, and the age structure of the population. Analysis of variance and covariance of the components of production showed that; (1) production within a site depended on the year; and (2) variation in total production was the result of variation in somatic and shell production as gamete production was relatively constant in the populations examined. In response to poor environmental conditions, D. polymorpha shift the allocation of resources from growth (somatic and shell) to reproduction. As individuals have no means of predicting how long adverse conditions will persist, investment in growth is unprofitable