Larval dynamics of a riverine metapopulation


Stoeckel, J. A., D. W. Schneider, L. A. Soeken, K. D. Blodgett, and R. E. Sparks. 1997.
Larval dynamics of a riverine metapopulation: Implications for zebra mussel
recruitment, dispersal, and control in a large-river system. Journal of North
American Benthological Society 16(3):586 601. Reprinted by U.S. Geological
Survey, Environmental Management Technical Center, Onalaska, Wisconsin,
January 1998. LTRMP 98-R001. 16 pp.  (NTIS #  PB98-124563)


ABSTRACT

Zebra mussels (Dreissena polymorpha) in the Illinois River are likely to function as a
metapopulation (a system of local populations connected by dispersal). River currents
reduce or eliminate internal recruitment by local populations, making them dependent
upon external recruitment from propagules (larvae) produced by upriver populations.
Because of the importance of external recruitment, understanding the population
dynamics of riverine zebra mussels requires knowledge of larval flux. In 1994 and 1995,
larval drift past a fixed site on the Illinois River was characterized by pulses of
similar-sized individuals. These pulses were composed primarily of D-stage (straight
hinge) larvae, not yet competent to settle. The continual passage of pulses of young
larvae suggests that the upriver source population(s) spawned in frequent distinct bursts
throughout the summer months rather than spawning only once or twice. Overall larval
abundance was a poor predictor of availability of competent larvae. Although larvae were
frequently present in high numbers, larvae >200  m in shell height (competent to settle)
were present only sporadically at our fixed study site from May to November in 1994,
and present only from June to early July in 1995. Settlement at a given site on the Illinois
River is likely to be sporadic rather than constant. Colonization and population growth at
a given site will occur only if suitable habitat and environmental conditions are available
during the windows when competent larvae are available. Changes in mean size as a
larval cohort drifted downriver suggested a growth rate of 6.72  m/d. At this growth rate,
most larvae probably travel a minimum of 304.6 km (190.4 miles) before settling. Thus,
larvae spawned in the main channel of the lower 70% of the Illinois River are most likely
to settle in the Mississippi River. We suggest that colonization and population growth in
the upper 70% of the Illinois River are strongly dependent upon larvae produced at
upriver source sites in Lake Michigan and the Chicago area waterways. Control of zebra
mussels in a given stretch of the river will depend upon control of the upriver source
populations. 


KEYWORDS

Control, dispersal, Dreissena polymorpha, larvae, metapopulation, recruitment, zebra
mussel