Jouko Sarvala

Learn More
The sources of carbon for the pelagic fish production in Lake Tanganyika, East Africa, were evaluated in a comprehensive multi-year study. Phytoplankton production was assessed from seasonal in situ 14C and simulated in situ results, using on-board incubator measurements and knowledge of the vertical distributions of chlorophyll and irradiance.(More)
Determinations of chlorophyll a and in vivo fluorescence of photosynthetic pigments were used to study vertical and horizontal distribution of phytoplankton in Lake Tanganyika (East Africa). Blue excited fluorescence (IVFb) was an approximate predictor of chlorophyll a at different depths and locations. Green excited fluorescence (IVFg), which reflects(More)
We studied the potential nutrient limitation of phytoplankton by means of seston nutrient stoichiometry and nutrient enrichment bioassays in the epilimnion of Lake Tanganyika. In most cases, the particulate carbon to phosphorus (C:P) ratio was high and indicated moderate P deficiency, while the respective C:N ratio mainly suggested moderate N deficiency.(More)
The harpacticoid copepod Canthocamptus staphylinus (Jurine) was shown to reproduce parthenogenetically in an oligotrophic Finnish lake. The population was univoltine with peaks of egg production in winter and early spring. Young from both peaks became adults in spring and aestivated as cysts. Laboratory experiments suggested that either high temperature (12(More)
Fish play a key role in the trophic dynamics of lakes. With climate warming, complex changes in fish assemblage structure may be expected owing to direct effects of temperature and indirect effects operating through eutrophication, water level changes, stratification and salinisation. We reviewed published and new long-term (10–100 years) fish data series(More)
We used a bioenergetics model to estimate daily food consumption of young-of-the-year (YOY) and adult vendace in the mesotrophic Lake Pyhäjärvi. Weekly samples of fish and zooplankton, plus temperature data, were collected from May to October 1987, to describe the growth and diet of vendace. The estimates of population size were based on spring abundance of(More)
The volume of limnological research in Finland has considerably expanded during recent decades, especially in the 1970s, with elevated funding and improved study facilities. Projects have become larger, the publication has intensified and has been increasingly directed to refereed international journals. The number of aquatic scientists has increased, new(More)
The pathogenicity of female Philometra obturans (Prenant, 1886) was investigated. Fish samples were taken in May and June 2001 from Lake Littoistenjärvi, in southwest Finland. The intensity of infection varied between 1 and 4 worms, these being found in the afferent artery of the 2 outermost gill arches. The prevalence was 33.9% (n = 59). Host condition and(More)
Our study aims to estimate confounded effects of nutrients and grazing zooplankton (Crustacea) on phytoplankton groupsdspecifically on nitrogen-fixing Cyanobacteriadin the shallow, mesotrophic Lake Pyhäjärvi in the northern hemisphere (Finland, northern Europe, lat. 60 54 0e 61 06 0, long. 22 09 0e22 22 0). Phytoplankton is modelled with a non-linear(More)