Quantification and comparisons of the structure of open-water plankton communities from 25 inland lakes of Ontario, from the Laurentian Great Lakes Superior, Huron, St. Clair, Ontario, and Erie, and from the Central Gyre in the North Pacific Ocean were made on the basis of the normalized biomass size spectrum. Residual variation around the fitted straight lines (corresponding to a theoretical steady state) was least for the large, oligotrophic Lake Superior and the North Pacific Gyre and greatest for eutrophic Saginaw Bay and shallow Lake Erie, suggesting progressive departure from steady-state conditions with increasing system productivity. The slopes of the normalized spectra decrease with increasing eutrophy, indicating that nannoplankton abundances are similar in all communities studied, but that associated zooplankton abundances vary by 2.5 orders of magnitude. Our results suggest that parameterization of particle-size models for prediction of potential fish production must be adjusted according to the size and productivity of the ecosystem, and that routine monitoring of communities by the normalized biomass spectrum could provide early warning of nutrient or toxic stress in aquatic ecosystems.

Species composition of phytoplankton in the Laurentian Great Lakes, its biomass concentration, and its physiological activity measured as photosynthesis related to eutrophication, are reviewed and discussed.

Derrnott, R., and M. Munawar. 1993. Invasion of Lake Erie offshore sediments by Breissena, and its ecological implications. Can. j. Fish. Aquat. Sci. 58: 2298-2304.Large populations sf the exotic rounded (noncarinate) shelled mussel sf the genus Breissena were found to exist on soft sediments collected throughout the central and eastern basins of Lake Erie during July and August 1992. Two different phenotypes were present on fine sediments (91 50 ym) in the eastern basin. An elongated white morph was common on the profundal sediments beyond 40 rn depth, while the "quagga" mussel was common on sand and sandy silt at depths between 10 and 30 rn. Together with the carinated zebra mussel Breissena pslg/larsrpha, which is very abundant on hard substrates in the sublittoral region, at least 80% of bake Erie's bottom sediments have been invaded by Dre-eissena. Only that region of the central basin (near Cleveland) which undergoes periodic summer anoxia was not inhabited by this genus. B e grandes populations de moule exotique 2 csquille arrondie (non carknke) appartenant au &enre Breissena ont 6tk observees sur des skdiments mous recueillis dans les bassins du centre et de I'est du lac Erik, en juillet et en aoOt 1992. Deux phknotypes diffbrents se trouvaient dans des sediments fins (9 150 pm) dans le bassin de I'est. Une forme blanche allsngbe &it co~srante sur les sediments profonds plus de 40 rn de profondeur, tandis que [a rnoule (( quagga )) etait courant sur le sable et le limon sableux, 2 des profondeurs comprises entre 18 et 38 m. La rnoule zebr6e carknke Dreissena polporpha est tres abondante sur Ies substrats durs de la rkgion jnfralittorale; ensemble, les trois types de Dreissena ont colonis6 au rnoins 80% des sediments de fond du lac Erik. Seule la region du bassin central (pr& de Cleveland) qui subit des periodes d'anoxie en 6t4 nf@tait pas envahie par ce genre.

in, and J. Love. 1995. Biomass size spectrum of the bake Michigan pelagic food web. Can. J. Fish. Aquat. Sci. 48: 105-1 15.Biomass size spectra for the complete Lake Michigan pelagic food web from picoplankton to salmonids were constructed for nine sampling transects around the lake in May and in September 1987. Size spectra were typical for freshwaters, having distinct peaks corresponding to major size groups. Biomass concentration of algae, zooplankton, and planktivores conformed to park-icle-size model predictions, but piscivore biomass was lower than predicted because these species are stocked. Mean annual total pelagic biomass was 72.3 g-m-' compared with a predicted range of 78.8-85.3 g~m-'. Potential production of piscivores, Mysis, and Pontopsreia was in agreement with model predictions, No estimates of zooplankton or planktivsre production were available, but we calculated that these could be 72.1-91 .€I and 2.54.8 g.m-2-yr-', respectively. Our analyses suggest that piscivore production is constrained by food web structure. Bloater, which comprise 72% of planktivore biomass, make up less than 20% of salmon diets. We estimate that piscivore production could be double the current value of 0.27 g.rn-'-yr-' if the forage fish community changed to include species more available to salmon. T he biomass size spectrum of an aquatic ecosystem is the communities comprising hundreds of species representing many distribution of living biomass across the range of organtmphic gmups. They have provided insight into various ecsism size. Such spectra me tractable s a a m~e s of complex logical processes in mari nme and freshwater ecosystems, including structure (Sheldon et al. 1972; ~chwin~hamir 198 1; Peters 'This paper is one of a series originating from a special session of 1983; ~~d r i~~~~ and ~~l l i~ 1986; sprules M~~~~~ 1986;

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