Percid fishes are found in lakes that cover a wide range of trophic conditions. The responses of percids and their habitats to progressive cultural eutrophication are predictable. Alterations in physicochemical characteristics of habitats precipitate changes in phytoplankton, macrophytes, zooplankton, and benthos that are ultimately deleterious. Enrichment can lead to favorable responses in percids, but somewhere in the continuum of trophic conditions the responses become unfavorable. The relative level at which the response becomes negative varies with the species according to tolerances to altered environment, adaptabilities to new habitat and forage base, and reproductive behavior. Progressive eutrophication acts as a selective mechanism that leads to a predictable sequence of fish species. Other perturbations, such as exploitation and habitat modification, can act synergistically with cultural eutrophication in accelerating the sequence. As eutrophication proceeds, the succession of species may not lead to increased fish yield because part of the nutrient load may be channeled through unharvestable food chains. Key words: Percidae, habitat, eutrophication, species dominance, food habits, parasitism, disease

Production rates (P) by benthic macroinvertebrates, obtained from data on instantaneous growth rate and biomass (B), ranged from 0.26 kcal m−2 day−1 at the inner bay station to 0.80 in the outer bay, 0.19 at the bay mouth, 0.16 outside the Bay of Quinte, and 0.04 in the main basin of Lake Ontario. Respiration rates (R) of the common species were fitted to the general model logeR = a1T + a2 logeW, where T is temperature and W is animal weight. Q10's averaged 3.5 and exponents of animal weight averaged 0.74. Growth efficiencies (production as a proportion of assimilation) declined progressively from about 0.65 at the inner bay station to 0.35 at the Lake Ontario station. Annual turnover ratios (P:B ratios) declined from 13 in the inner bay to about 1 in the deep sediments of Lake Ontario. Turnover ratio (TR) was correlated with mean annual bottom temperature (T), [Formula: see text], and production was predicted by [Formula: see text].

The history of Great Lakes benthic research from 1870 to the present is briefly reviewed. An examination of the status of taxonomic work on benthic components, and a consideration of the zoogeographical history of the benthos leads to a discussion of bottom communities and macroinvertebrate production in the five major lakes.Profundal communities throughout the lakes are dominated by the glaciomarine relict amphipod Pontoporeia affinis and various species of Oligochaeta, Sphaeriidae, and Chironomidae. The specific composition of these components, and natural and recently imposed changes in their proportions within communities are examined. Population densities and standing stocks, and the proportion of oligochaetes in communities, all tend to increase in response to a natural gradient in productivity inferred from increasing concentrations of parameters such as organic matter and water hardness. Man's influence on water quality anywhere along this gradient compounds the effects of natural factors towards tubificid communities of predictable species composition: Limnodrilus hoffmeisteri, L. claparedeianus, L. cervix, L. maumeensis, Peloscolex multisetosus, and often Tubifex tubifex. The ameliorating influence of water depth is shown in Lake Erie where the change in community composition reflects improving profundal water quality from west to east — a reversed model of the Great Lakes system as a whole.

Present, background, and anthropogenic loading rates of Cu, Ni, Zn, Pb, Cd, Cr, Hg, As, and Se to lake sediments were calculated from 210Pb dated cores, and present loading rates were compared with concentrations in several fishes. Present loadings of Pb averaged 17 times background loadings and all lakes had statistically significant anthropogenic inputs. The majority of lakes had anthropogenic loadings of Zn, Cd, Hg, and As, which were presently 1.8–2.6 times background loadings. For Ni, Cu, Se, and Cr, only seven, five, two, and one lake(s), respectively, had significant anthropogenic inputs, and the means of present: background loadings for all lakes were not significantly different from 1.0. Enrichment by Zn, Cd, As, and especially Pb was greater closer to industrialized regions, while Hg enrichment was more widespread. Anthropogenic and precipitation loadings for Zn, Pb, Cd, and As were similar, suggesting that anthropogenic inputs are atmospheric and that current atmospheric loadings are mostly anthropogenic. [Hg] and [Cd] in fish were correlated with loadings to sediments, but [Cu] and [Zn] in fish were relatively constant within species, supporting the hypothesis that contaminants in fish would be correlated with inputs to sediments, while trace nutrients in ample supply would be unrelated to loading. [Cr] and [Se] in fish were intermediate in response to loading, but correlation between [Pb] in fish and loadings was not detected.

Commonest lake types of the 15 combinations of four fish species (walleye, Stizostedion vitreum vitreum; northern pike, Esox lucius; lake trout, Salvelinus namaycush and smallmouth bass, Micropterus dolomieui) were walleye–pike (22%), pike "only" (19%), lake trout "only" (16%) and smallmouth bass "only" (10%). Lake trout–walleye and lake trout–walleye–smallmouth bass types were extremely rare. Lake depth and area were variables of greatest significance in distinguishing lake types by discriminant analysis. Climatic factors explained the general geographic distribution of smallmouth bass. Hypotheses to explain the low frequency of walleye in small lakes include possibilities of (1) low probability of successful coexistence of pike and walleye, (2) lack of wind fetch to clear spawning areas, and (3) "Lebensraum requirement" of the walleye. Key words: limnology, Percidae, methodology, Ontario lake types, Stizostedion vitreum vitreum, Esox lucius, Salvelinus namaycush, Micropterus dolomieui, distribution, associations