Jyrki Lappalainen

Effects of clay turbidity and density of pikeperch (Sander lucioperca) larvae on predation by perch (Perca fluviatilis)

Increased turbidity reduces visibility in the water column, which can negatively affect vision-oriented fish and their ability to detect prey. Young fish could consequently benefit from high turbidity levels that can provide a protective cover, reducing predation pressure. Perch (Perca fluviatilis) are commonly found in littoral zones of temperate lakes and coastal areas of the Baltic Sea. Pikeperch (Sander lucioperca) spawn in these areas, so perch is a potential predator for pikeperch larvae. We conducted laboratory experiments to test the predation of perch on pikeperch larvae at different turbidity levels (5–85 nephelometric turbidity units), densities of pikeperch larvae (2–21 individuals l−1) and volumes of water (10–45l). The logistic regression showed that the probability of larvae eaten depended significantly on turbidity and volume of water in the bags, while density of larvae was not significant. However, because container size is known to affect predation, the data was divided into two groups based on water volume (10–20 and 25–45l) to reduce the effects of container size. In either group, probability of predation did not significantly depend on volume, whereas turbidity was significant in both groups, while density was significant in larger water volumes. Thus, high turbidity impaired perch predation and protected pikeperch larvae from perch predation. Because density of larvae was also a significant factor affecting predation of perch, the dispersal of pikeperch larvae from spawning areas should also increase the survival of larvae.

Implications of rudd (Scardinius erythrophthalmus) herbivory on submerged macrophytes in a shallow eutrophic lake

The role of rudd (Scardinius erythrophthalmus) herbivory was studied in Kirkkojärvi, a shallow and turbid basin in Lake Hiidenvesi, Finland. The submerged species dominating in the rudd diets were Potamogeton obtusifolius, Ranunculus circinatus, Sparganium emersum, bryophytes, and filamentous algae. Plant consumption estimated with bioenergetics modelling increased with fish age, being highest in late summer concomitant with the macrophyte biomass peak. Depending on the age structure, a rudd biomass of 20 kg ha−1 consumes 18–23 kg of macrophytes ha−1 a−1, while a rudd biomass of 100 kg ha−1 results in plant consumption of 92–115 kg ha−1 a−1. Although, rudd seemed to feed rather unselectively on suitable-sized and edible plants, some species abundant in the littoral, such as Myriophyllum verticillatum and pleustophytic Ceratophyllum demersum, were not found in rudd guts, indicating selective plant consumption. In Kirkkojärvi, selective grazing by rudd and increased turbidity and high nutrient levels partly caused by bottom dwelling cyprinid fish, may promote the inedible and pleustophytic macrophytes, which have increased in Kirkkojärvi during the past decades.

A comparative analysis of metacommunity types in the freshwater realm

Most metacommunity studies have taken a direct mechanistic approach, aiming to model the effects of local and regional processes on local communities within a metacommunity. An alternative approach is to focus on emergent patterns at the metacommunity level through applying the elements of metacommunity structure (EMS; Oikos, 97, 2002, 237) analysis. The EMS approach has very rarely been applied in the context of a comparative analysis of metacommunity types of main microbial, plant, and animal groups. Furthermore, to our knowledge, no study has associated metacommunity types with their potential ecological correlates in the freshwater realm. We assembled data for 45 freshwater metacommunities, incorporating biologically highly disparate organismal groups (i.e., bacteria, algae, macrophytes, invertebrates, and fish). We first examined ecological correlates (e.g., matrix properties, beta diversity, and average characteristics of a metacommunity, including body size, trophic group, ecosystem type, life form, and dispersal mode) of the three elements of metacommunity structure (i.e., coherence, turnover, and boundary clumping). Second, based on those three elements, we determined which metacommunity types prevailed in freshwater systems and which ecological correlates best discriminated among the observed metacommunity types. We found that the three elements of metacommunity structure were not strongly related to the ecological correlates, except that turnover was positively related to beta diversity. We observed six metacommunity types. The most common were Clementsian and quasi-nested metacommunity types, whereas Random, quasi-Clementsian, Gleasonian, and quasi-Gleasonian types were less common. These six metacommunity types were best discriminated by beta diversity and the first axis of metacommunity ecological traits, ranging from metacommunities of producer organisms occurring in streams to those of large predatory organisms occurring in lakes. Our results showed that focusing on the emergent properties of multiple metacommunities provides information additional to that obtained in studies examining variation in local community structure within a metacommunity.

Climate Warming and Pikeperch Year-Class Catches in the Baltic Sea

Climate change scenarios concerning the Baltic Sea predict increase in surface water temperatures. Pikeperch (Sander lucioperca (L.)) inhabits the coastal areas of the northern Baltic Sea and is an important fish species for the Finnish fisheries. The year-class strength of pikeperch varies strongly between years and significantly depends on water temperature. We aimed to study the effects of changing temperature conditions on pikeperch fisheries and distribution based on commercial catch data from the period 1980–2008 in the Finnish coastal areas of the Baltic Sea. The results indicated that warmer summers will produce stronger pikeperch year-classes that consequently contribute significantly to the future catches. The average temperature in June–July explained 40% of the variation in the year-class catches in the Gulf of Finland and 73% in July–August in the Archipelago Sea. During the study period, the distribution of pikeperch catches expanded toward north along the coasts of the Bothnian Sea.

Latitudinal gradients in niche breadth and position—regional patterns in freshwater fish

The latitudinal gradient in diversity is widely acknowledged, but the mechanisms contributing to this pattern are still poorly known. Given that the species have environmental optima, a central issue is how species’ niche parameters, i.e. niche breadth and niche position, vary along the latitudinal gradient. In this study, we examined the determinants of fish distribution and the variability in species’ niche breadth and position along latitudinal gradient using a regional data set of boreal lakes. Results of the Outlying Mean Index analysis showed that the fish community structure was jointly controlled by a number of environmental factors, ranging from water chemistry and temperature to local physical factors such as lake area and depth. Corroborating the number of earlier findings, the regional occupancy of species was more strongly governed by the niche position than the niche breadth, although both showed a significant relationship with the regional distribution. When the latitudinal variability in niche parameters of the main taxonomic groups was analysed, both percids and cyprinids, being cool water species, showed significant decrease in niche breadth northwards as we predicted. By contrast, the niche position and latitude were non-significantly correlated in percids and salmonids, and negatively correlated in cyprinids, the latter showing the opposite pattern as we predicted. However, even if only a part of our predictions was supported, the results generally implied that the examination of latitudinal variability in the niche properties is potentially highly rewarding, not only in estimation of present community structure in lakes but also for predictions of species’ responses to climate change.

Metacommunity ecology meets biogeography: effects of geographical region, spatial dynamics and environmental filtering on community structure in aquatic organisms

AbstractMetacommunity patterns and underlying processes in aquatic organisms have typically been studied within a drainage basin. We examined variation in the composition of six freshwater organismal groups across various drainage basins in Finland. We first modelled spatial structures within each drainage basin using Moran eigenvector maps. Second, we partitioned variation in community structure among three groups of predictors using constrained ordination: (1) local environmental variables, (2) spatial variables, and (3) dummy variable drainage basin identity. Third, we examined turnover and nestedness components of multiple-site beta diversity, and tested the best fit patterns of our datasets using the “elements of metacommunity structure” analysis. Our results showed that basin identity and local environmental variables were significant predictors of community structure, whereas within-basin spatial effects were typically negligible. In half of the organismal groups (diatoms, bryophytes, zooplankton), basin identity was a slightly better predictor of community structure than local environmental variables, whereas the opposite was true for the remaining three organismal groups (insects, macrophytes, fish). Both pure basin and local environmental fractions were, however, significant after accounting for the effects of the other predictor variable sets. All organismal groups exhibited high levels of beta diversity, which was mostly attributable to the turnover component. Our results showed consistent Clementsian-type metacommunity structures, suggesting that subgroups of species responded similarly to environmental factors or drainage basin limits. We conclude that aquatic communities across large scales are mostly determined by environmental and basin effects, which leads to high beta diversity and prevalence of Clementsian community types.

Effects of water temperature on year-class strengths and growth patterns of pikeperch (Sander lucioperca (L.)) in the brackish Baltic Sea

Pikeperch (Sander lucioperca), the studied species, is the most important amongst freshwater fish species, commercially, in the brackish Baltic Sea. We studied the effects of water temperature on three aspects of pikeperch growth in Haminanlahti bay, Finland. First, annual length increments were related to age and temperature using a non-linear growth model. Since length increments were based on back-calculated lengths, i.e. repeated measurements, the first order autoregressive covariance structure was used. The model showed that when temperature increased annual length increments also increased, whereas increased age reduced annual length increments. In the modelling, the best fit was found with water degree-days over 10°C. Second, the onset of growth of pikeperch in spring had a positive relationship with water temperature and a negative one with the length of pikeperch. The latter finding suggests that smaller, non-mature pikeperch starts to grow earlier than larger, mature pikeperch. Third, the year-class strength was positively correlated with water degree-days, and the year-class strength negatively affected annual length increments. This indicates that within a strong year-class subsequent growth is reduced more that within a weak year-class, suggesting density-dependent growth.

Ecological and Life History Characteristics of Ruffe (Gymnocephalus cernuus) in Relation to Other Freshwater Fish Species

Abstract Ecological and life history characteristics of ruffe (Gymnocephalus cernuus) were studied in relation to 33 other native freshwater fish species in Finland. The descriptive ecological characteristics included 1) trophic guild, 2) species interaction, 3) adult habitat, 4) spawning habitat, 5) reproductive behavior, and 6) reproductive guild. The life history variables included 1) age at maturity, 2) length at maturity, and 3) fecundity as a number of eggs. Three different clusters of fish species were found in cluster analysis based on the ecological characteristics. The most distinct cluster of 7 species was comprised of predators. Ruffe was grouped into the largest cluster together with 20 other species and was closest to the cyprinid, gudgeon (Gobio gobio). In multidimensional scaling species were placed in two hypothetical dimensions firstly by their interaction with other species, trophic guild and adult habitat and secondly by their spawning habitat. Ruffe was placed near the center of the plot, suggesting that it has no special ecological requirement among the characteristics and species studied. Subsequent analysis of the life history characteristics revealed that ruffe was similar to the most typical r-selected species in Finland, showing high fecundity and low length at maturity, but with slightly slower growth rate. We, therefore, concluded that adult ruffe is a potential invader species showing no special ecological requirements and with life history characteristics typical for r-selected species.

The impact of trout introductions on macro- and micro- invertebrate communities of fishless boreal lakes

Abstract Effects of fish introductions on lake ecosystems have long been debated. It has been hypothesized that such effects should be strongest in oligotrophic lakes, where fish were not originally present. We investigated two lakes (one naturally fishless, one fish-stocked in 1980) in northern Fennoscandia, selected because of the absence of other anthropogenic stressors and a well-known stocking history. The diet of the introduced brown trout (Salmo trutta L.) was analysed to estimate the effect of their predation on the pelagic invertebrate communities. Quantitative and qualitative samples were taken to assess the current abundances of pelagic macro- and micro-invertebrates in different habitats of both lakes, to infer the impact of brown trout presence. Past abundances of Cladocera, Chironomidae, Gammaruslacustris and Daphnia longispina were also estimated based on subfossil remains in the sediment, and used to assess how brown trout introduction affected macro- and micro-invertebrates living in different habitats. Relative abundance and species richness of Cladocera were evaluated in sediment cores from both lakes, to assess whether changes were caused by fish-introduction-induced trophic cascades or climate change. Also, planktonic Cladocera (Eubosmina) body sizes were measured to evaluate their response to the release of macro-invertebrate predation pressure. Brown trout introduction displaced macro-invertebrates, i.e. G. lacustris, from the pelagic area, and caused a trophic cascade effect that slightly increased the species richness of Cladocera, but markedly increased their abundance, as shown in the sediment record. Introduced brown trout did not, however, cause a decline in Chironomidae, G. lacustris or D. longispina abundances. On the contrary, it resulted in an approximately five-fold increase in Chironomidae accumulation rates in the sediment. The release of macro-invertebrate predation pressure did not lead to changes in the body shapes of Eubosmina, which could be a consequence of the composition of the original macro-invertebrate species assemblage.

Stunted growth of pikeperch Sander lucioperca in Lake Sahajärvi, Finland

Growth of pikeperch Sander lucioperca in the eutrophic and clay-turbid Lake Sahajärvi, Southern Finland, was extremely slow in comparison with other lakes at similar latitudes. The most important food item in July was phantom midge larvae Chaoborus flavicans for all sizes of S. lucioperca (239-423 mm total length L(T)), while later, in August and September, the diet of S. lucioperca (149-407 mm L(T)) consisted of small (30-100 mm L(T)) perch Perca fluviatilis, ruffe Gymnocephalus cernuus and roach Rutilus rutilus.