Jouko Sarvala

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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)
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 0 e 61 06 0 , long. 22 09 0 e22 22 0). Phytoplankton is modelled with a non-linear(More)
Säkylän Pyhäjärvi (SW Finland) is an example of a large and shallow lake suffering from eutrophication. During the last 20 years, the quality and general usability of water in Pyhäjärvi have shown considerable variation driven by both a variety of human activities and climate-related factors such as wet and dry years. The lake has been thoroughly studied(More)
Lake Tanganyika, the deepest and most voluminous lake in Africa, has warmed over the last century in response to climate change. Separate analyses of surface warming rates estimated from in situ instruments, satellites, and a paleolimnological temperature proxy (TEX86) disagree, leaving uncertainty about the thermal sensitivity of Lake Tanganyika to climate(More)
Medusae are important members of marine food webs, but are rare in lakes. In one of the largest lakes in the world, Lake Tanganyika, a small medusa (Limnocnida tanganyicae) is a prominent component of zooplankton. We used field and laboratory methods to study the ecological role of Lake Tanganyika medusae, which occasionally reached high local densities in(More)
Lake Säkylän Pyhäjärvi has been an important fishing site and drinking water source for the local population for centuries. The lake has undergone significant changes: (1) the water level was lowered in the 1600s and in the 1850s; (2) planktivorous coregonid fish were successfully introduced in the early 1900s; (3) nutrient input from intensified(More)
The offshore pelagic niche in Lake Kariba is mainly occupied by the Tanganyika sardine, Limnothrissa miodon, commonly called ‘kapenta’, which is a mainly zooplanktivorous clupeid fish. The population dynamics of kapenta fluctuate seasonally in synchrony with the physical processes that shape the trophic status of the lake. Diel feeding periodicity and mean(More)
Fish are known for their high phenotypic plasticity in life-history traits in relation to environmental variability, and this is particularly pronounced among salmonids in the Northern Hemisphere. Resource limitation leads to trade-offs in phenotypic plasticity between life-history traits related to the reproduction, growth, and survival of individual fish,(More)
The concern for the state of global freshwater reservoirs has increased due to deterioration of the water quality during the last decades. This has prompted monitoring and restoration efforts such as the European Water Framework Directive and the national-scale 2nd-investigation and monitoring of the water quality, water volume and biota resources in China.(More)
1. INTRODUCTION 4 1.1 Aquatic ecosystem functioning 4 Role of trophic structure 4 Aquatic ecosystem responses to nutrient enrichment 5 1.2 Littoral ecosystems 6 Community structure in littoral habitats 6 Relative roles of macrophytes and zooplankton in controlling phytoplankton biomass 7 1.3 Ecosystem regime shifts 9 1.4 Changes in the functioning of(More)