Suppression of microzooplankton by zebra mussels: importance of mussel size

1. The zebra mussel (Dreissena polymorpha) is amongst the most recent species to invade the Great Lakes. We explored the suppressive capabilities of mussels 6–22‐mm in size on Lake St Clair microzooplankton ( \u3c 240)μm) in laboratory experiments. 2. Absolute suppression of rotifers and Dreissena veliger larvae was proportional to mussel shell length for individuals larger than 10 mm; larger zooplankton, mainly copepod nauplii and Cladocera, were not affected. Mussel clearance rates on rotifers generally exceeded those on veligers, although rates for both increased with increasing mussel size. Rotifer‐based clearance rates of large (22 mm) mussels approached published values for phytoplankton food. 3. Most zooplankton taxa, particularly rotifers, declined significantly in western Lake Erie during the late 1980s concomitant with the establishment and population growth of zebra mussels in the basin. Densities of some taxa subsequently increased, although rotifers and copepod nauplii densities remained suppressed through 1993. Available evidence indicates that direct suppression by Dreissena coupled with food limitation provides the most parsimonious explanation for these patterns. Copyright © 1995, Wiley Blackwell. All rights reserve

Elastic constants of niobium-zirconium, hafnium, and tungsten alloys

The adiabatic single-crystalline elastic constants of pure niobium, Nb-Zr, Nb-Hf, and Nb-W alloys were determined in the temperature range 77-298 °K. An unusual temperature dependence was noted in the Nb-rich alloys which may be related to the shape of the Fermi surface. Zr and Hf alloying additions decrease the value of C′, which indicates decreasing bcc lattice stability. The values of the elastic anisotropy ratio C44/C′ follow the behavior predicted by Fisher, which indicates that the elastic shear moduli are closely related to the filling of the d band. The Debye temperatures cursive-theta signD were calculated, and W additions tend to increase cursive-theta signD, while Zr and Hf lower cursive-theta sign D