The community structure of littoral macroinvertebrates was explored by multivariate analyses in three basins of the large Lake Saimaa system (eastern Fin land). The basins differed in trophic status and degree of human influence. It was hypothesized that the structure of littoral invertebrate communities is influenced by lake trophic status, as is the case in profundal communities. Three littoral habitat types with different substrate (stony, sandy and vegetated shores) were sampled from the shoreline to a depth of 1.5-3 meters. The habitat type was found to be largely deter mined by the slope of the shore and the wind exposure. Each habitat type supported fairly characteristic fauna, and detrended correspondence analysis grouped the inverte brate assemblages by habitat type rather than by basin. Within each habitat type, canonical correspondence analysis indicated that species composition changed along the trophic gradient. In the vegetated littoral zone, the greatest change in community structure occurred within the macrophyte beds, varying from the outer edge of macro phytes to the shoreline. Two alternative or complementary explanations are given for this horizontal gradient. First, a horizontal gradient of abiotic characteristics results in a change of community composition. Second, the macrophyte beds may form a hori zontal transition zone in predation, from invertebrate predation inshore to fi sh preda tors offshore. On the stony and sandy shores, the magnitude of wave action was also important in structuring the communities. As each habitat type harbors characteristic

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The two most commonly used methods for estimating the food consumption of fish are based on either the evacuation rate of food or the energy budget of an individual fish. In this study, both of those methods were used to estimate the food consumption of fish under experimental conditions. Bioenergetics models of vendace Coregonus ulbulu, smelt Osmrrus cperlunus, roach Rutilus rutilus and perch Percu fluviutilis were reconstructed based on experimental data and published values. The precision of the bioenergetics estimates for food consumption was evaluated under experimental conditions. The modelling efficiency (EF) of the bioenergetics model was 0.90, 0.97 and 0.93 for coregonids, roach and perch, respectively, which indicated good agreement between observed and predicted values. Under our experimental conditions, the bioenergetics model estimated food consumption better than the evacuation rate model. :c' 1997 The Fisherrcs Society of the British Isles

Heat fluxes at the lake surface play an integral part in determining the energy budget and thermal structure in lakes, including regulating how lakes respond to climate change. We explore patterns in turbulent heat fluxes, which vary across temporal and spatial scales, using in situ high‐frequency monitoring data from 45 globally distributed lakes. Our analysis demonstrates that some of the lakes studied follow a marked seasonal cycle in their turbulent surface fluxes and that turbulent heat loss is highest in larger lakes and those situated at low latitude. The Bowen ratio, which is the ratio of mean sensible to mean latent heat fluxes, is smaller at low latitudes and, in turn, the relative contribution of evaporative to total turbulent heat loss increases toward the tropics. Latent heat transfer ranged from ~ 60% to > 90% of total turbulent heat loss in the examined lakes. The Bowen ratio ranged from 0.04 to 0.69 and correlated significantly with latitude. The relative contributions to total turbulent heat loss therefore differ among lakes, and these contributions are influenced greatly by lake location. Our findings have implications for understanding the role of lakes in the climate system, effects on the lake water balance, and temperature‐dependent processes in lakes.

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Biomass and species diversity (richness and evenness) of littoral organisms were explored in 27 sites in three basins of the large Lake Saimaa system in eastern Finland. The basins differed in degree of nutrient loading and trophic status. Six organismal groups, i.e., phytoplankton, periphyton, macrophytes, crustacean zooplankton, benthic macroinvertebrates and fish were studied. Factors affecting the biomass and diversity of these groups were explored by multiple stepwise regression analysis. The biomass of different groups was explained by the same variables, mainly nutrients, while diversity was associated with different environmental factors among the studied groups. The biomass of periphyton, phytoplankton, zooplankton, and fish correlated significantly with each other. There was also an apparent association between the biomass of macrophytes and that of benthic invertebrates. However, no significant correlations were found among the diversity of the studied groups. In accordance with previous studies, our results did not support the existence of species-rich hotspots or the possibility of using any surrogate taxon to reveal overall biodiversity. Thus, for conservation planning, biological surveys should include extensive collection of taxonomic groups and organisms at all trophic levels.

The temperature relationship of routine metabolic rate (R r ) of non-feeding, non-growing Coregonus lavaretus larvae between 2 and 15 C is characterized by Q 10 -values ranging from 1·8-2·45. The rate of growth, based on weight determinations, of first-feeding larvae amounted to 3·5, 7·6 and 9·4% day 1 at 5, 10 and 12 C respectively, from which Q 10 -values between 4·0 and 4·8 can be calculated. The rate of increase of muscle mass between 5 and 10 C, based on the determination of the cross-sectional area of inner muscle fibres, resulted in a Q 10 -value of 4·5. Water temperature influenced the pattern of growth of the inner muscle fibres. At hatching, after 360 day degrees, total muscle mass of larvae reared at 4 and 8 C was independent of temperature, but at 4 C the rate of mass increase owed more to hyperplasia (increase in fibre number) than to hypertrophy (increase in fibre mass), whereas at 8 C the opposite was the case. The calculation of power budgets (including the metabolic cost of growth) of first-feeding larvae yielded net conversion efficiencies (K 2 ) increasing with temperature from 46·3% at 5 C to 54·7% at 12 C. Comparing our data with literature data two general conclusions can be drawn. (1) In first-feeding larvae the net, but not the gross, conversion efficiency of food energy increases with temperature. This is due to net energy input being characterized by a much higher Q 10 -value than energy expenditures. (2) In embryos of freshwater fish so far investigated hyperplasia plays a greater role in the increase of fibre mass than hypertrophy at the lower temperature, whereas in embryos of marine fish hyperplasia prevails at the higher temperature. It is suggested that this discrepancy correlates with the high concentration of free amino acids in the eggs of marine species which provide an additional, easily available, source of metabolic energy absent in freshwater species. 1996 The Fisheries Society of the British Isles