Resource limitation during early ontogeny: constraints induced by growth capacity in larval and juvenile fish

The presence of and mechanisms behind density-dependent growth and resource limitation in larval and juvenile stages of organisms with high mortality such as fish are much debated. We compare observed consumption and growth rates with maximum consumption and growth rates to study the extent of resource limitation in young-of-the-year (YOY) roach (Rutilus rutilus) and perch (Perca fluviatilis). Diet, habitat use, consumption rate and growth rate were measured under varying YOY fish densities over 2 years in four lakes. In the first year, YOY roach and perch were studied under allopatric conditions. Experimental addition of perch roe in the second year also allowed study of YOY of the two species under sympatric conditions in two of the lakes. The diet of YOY roach was dominated by cladoceran zooplankton and YOY roach habitat use was restricted to the shore region in both years. This restricted habitat use did not involve any cost in foraging gain in the first year as consumption and growth rates were very close to maximum rates. During the second year, when the two species coexisted, resources were limited in late season, more so in the littoral than in the pelagic habitat in one lake while the reverse was the case in the other lake. The diet of YOY perch was also dominated by zooplankton, and with increasing perch size the proportion of macroinvertebrate prey in the diet increased. After hatching, YOY perch first utilized the pelagic habitat restricting their habitat use to the shore after 1 to several weeks in the pelagic zone. During the larval period, perch were not resource limited whereas juvenile perch were resource limited in both years. The fact that YOY perch were more resource limited than YOY roach was related to the higher handling capacity and lower attack rate of perch relative to roach, rendering perch more prone to resource limitation. Estimates of resource limitation based on consumption rates and growth rates yielded similar results. This supports the adequacy of our approach to measure resource limitation and suggests that this method is useful for studying resource limitation in organisms with indeterminate growth. Our results support the view that density-dependent growth is rare in larval stages. We suggest that density-dependent growth was absent because larval perch and roach were feeding at maximum levels over a wide range of larvae densities. Received: 14 June 1999 / Accepted: 29 October 1999     

Shifts in fish communities along the productivity gradient of temperate lakes—patterns and the importance of size-structured interactions

Species biomass and size composition of fish faunas along a productivity gradient were studied in south Swedish lakes. Generally, with increasing productivity (measured as chlorophyll content), Salmoniformes were replaced by percids, which in turn were replaced by cyprinids, as suggested in previous studies. However, percids showed two peaks in biomass, one in medium productive lakes due to perch and one in highly productive lakes due to zander. Benthic piscivores were present in all lakes, whereas pelagic piscivores were absent in the least productive lakes. The proportion of piscivores in the total fish biomass showed a peak in medium productive lakes, largely reflecting the importance of piscivorous perch. The median size of the dominant cyprinids (roach) in the systems studied increased as the importance of piscivores increased, which was interpreted as a size refuge response to increased predation pressure. The same pattern was present for the dominant planktivore, vendace, in low productive systems. Although a predictable pattern of change in the fish fauna was found along the productivity gradient, other environmental factors such as structural complexity may be the ultimate cause of the observed succession pattern.     

Intraspecific competition drives multiple species resource polymorphism in fish communities

It has been hypothesized that inter-specific competition will reduce species niche utilization and drive morphological evolution in character displacement. In the absence of a competitor, intra-specific competition may favor an expansion of the species niche and drive morphological evolution in character release. Despite of this theoretical framework, we sometimes find potential competitor species using the same niche range without any partitioning in niche. We used a database on test fishing in Sweden to evaluate the factors (inter- and intraspecific competition, predation, and abiotic factors) that could influence habitat choice of two competitor species. The pattern from the database shows that the occurrence of perch and roach occupying both littoral and pelagic habitats of lakes in Sweden is a general phenomenon. Furthermore, the results from the database suggest that this pattern is due to intra-specific competition rather than inter-specific competition or predation. In a field study, we estimated the morphological variation in perch and roach and found that, individuals of both species caught in the littoral zone were more deeper bodied compared to individuals caught in the pelagic zone. Pelagic perch fed more on zooplankton compared to littoral perch, independent of size, whereas the littoral perch had more macroinvertebrates and fish in their diet. Pelagic roach fed more on zooplankton compared to littoral roach, whereas littoral individuals fed more on plant material. Furthermore, we sampled littoral and pelagic fish from another lake to evaluate the generality of our first results and found the same habitat associated morphology in both perch and roach. The results show a consistent multi-species morphological separation in the littoral and pelagic habitats. This study suggests that intra-specific competition is possibly more important than inter-specific competition for the morphological pattern in the perch-roach system.     

Habitat shift in roach (Rutilus rutilus) induced by pikeperch (Stizostedion lucioperca) introduction: predation risk versus pelagic behaviour

Changes in the fish community structure and habitat use were followed after the introduction of pikeperch (Stizostedion lucioperca) to the roach-dominated Lake Gjersjøen. Quantitative echosounding showed that the density of juvenile roach (Rutilus rutilus) was dramatically reduced in pelagic areas, from 12 000–15 000 fish/ha to 250 fish/ha, while total fish density remained unchanged in littoral areas. At the same time, the habitat segregation between different size groups of roach was altered as larger roach utilized the pelagic zone after pikeperch introduction. The loss of the pelagic refuge for juvenile roach increased the availability of juvenile roach to littoral predators, notably perch. In littoral areas, the fish community changed from one dominated by roach (> 95%) to one dominated by perch (> 50%).     

Comparing two fish sampling standards over time: largely congruent results but with caveats

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Determinants of the distribution of juvenile fish in the littoral area of a shallow lake

1. Research has often focused on the pelagic areas of lakes; the littoral zone has received less attention. The few studies concerning fish distribution in littoral habitats have concentrated on stands of submersed macrophytes, whereas other littoral habitat types have seldom been investigated. 2. This study aimed to predict the occurrence of juvenile fish in several littoral habitats of a shallow lake as a function of food availability, complexity of habitat structure, water depth and substrate. Habitats comprising reed, woody structures, and two open water areas differing in depth were sampled for fish and invertebrate biomasses on two shores, over 6 months and during both daylight and at night. 3. The juvenile fish community consisted almost exclusively of 0+ and 1+ roach and perch. There was a strong diel component in habitat use, with a predominant occurrence of fish in complex habitats (mainly woody structures) during the day, and a partial migration towards the open habitats at night, more strongly expressed in roach than in perch. 4. The diet of all fish groups was relatively constant over the seasonal cycle, and was independent of habitat. There was a higher degree of planktivory in roach than in perch, but both species fed on benthic macroinvertebrates to a substantial extent. 5. According to a logistic regression model, the biomass of potential food organisms in the different habitats had little predictive effect on the spatial distribution of the fish, whereas the structural complexity of the habitats combined with the diel cycle explained about 28% of the occurrence patterns in 0+ and 1+ perch and 1+ roach.     

Seasonal changes in the diets and relative abundances of perch and roach in the littoral and pelagic zones of a large lake

In the Enonselkä and Laitialanselkä basins of Lake Vesijärvi, perch Perca fluviatilis and roach Rutilus rutilus were abundant in the littoral and in the pelagic zones throughout the summer. In the littoral zone, roach was always more numerous than perch, while perch dominated in the open water. Intraspecific diet overlap values were higher than interspecific values. In the pelagic zone, perch <155 mm fed mainly on the cladoceran Leptodora kindtii , while small bosminids were most important food items for roach. Large perch were piscivorous, feeding mainly on smelt Osmerus eperlanus . In the littoral zone small perch foraged on zooplankton and chironomid larvae and large perch on chironomids and fish (small perch). Small roach fed mainly on bosminids and detritus, while for roach <185 mm macrophytes ( Elodea Canadensis, Lemna trisulca ) were also of importance. Detritus was more common in the food of roach in Laitialanselkä than in Enonselkä. The slower growth rate of roach in Laitialanselkä compared with Enonselkä was probably connected with this. However, considering the latitude of the lake, the growth rate of both roach and perch was relatively fast in both basins. The results indicated that in a large lake both perch and roach are able to utilize effectively the different habitats and diverse food resources. By segregation in food resource utilization they are able to co-exist in large quantities, at the same time maintaining a relatively fast growth rate.     

Rapid changes in fish community structure and habitat distribution following the precipitation of lake phosphorus with aluminium

1. Fish community structure and habitat distribution of the abundant species roach, perch and ruffe were studied in Lake Nordborg (Denmark) before (August 2006) and after (August 2007) aluminium treatment to reduce internal phosphorus loading. 2. Rapid changes in fish community structure, abundance and habitat distribution occurred following a decline in in‐lake phosphorus concentrations from 280 to 37 μg P L^?1 and an increase in Secchi depth transparency from 1.1 to 1.9 m (August). The proportion of perch in overnight gill net catches increased, whilst roach decreased, and the average weight of all key species increased. 3. The habitat distribution of perch and roach changed from a high proportion in the upper pelagic and littoral zones in 2006, towards enhanced proportions in the deeper pelagic and profundal zone in 2007. The abundance of large‐bodied zooplankton increased and the abundance of benthic invertebrates decreased in the same period, suggesting that the habitat shift was not induced by food limitation. 4. Ruffe shifted from the littoral and upper profundal zones towards the deep profundal zone, likely reflecting an increased predation risk in the littoral zone and better oxygen conditions in the deep profundal. 5. Our results indicate that enhanced risk of predation in the upper pelagic and the littoral zones and perhaps improved oxygen concentrations in the deeper profundal zone at decreasing turbidity are responsible for the observed habitat shift. The results indicate that fish respond rapidly to changes in nutrient state, both in terms of community structure and habitat use.     

Trophic dynamics in a whole lake experiment: size-structured interactions and recruitment variation

Horizontal and vertical heterogeneity as a result of size‐structured processes are important factors influencing indirect effects in food webs. In a whole‐lake experiment covering 5 years, we added the intermediate consumer roach (Rutilus rutilus) to two out of four lakes previously inhabited by the omnivorous top predator perch (Perca fluviatilis). We focused our study on the direct consumption effect of roach presence on zooplankton (and indirectly phytoplankton) versus the indirect effect of roach on zooplankton (and phytoplankton) mediated via effects on perch reproductive performance. The patterns in zooplankton and phytoplankton abundances were examined in relation to population density of roach and perch including young‐of‐the‐year (YOY) perch in the light of non‐equilibrium dynamics. The presence of roach resulted in changed seasonal dynamics of zooplankton with generally lower biomasses in May–June and higher biomasses in July–August in roach lakes compared to control lakes. Roach presence affected perch recruitment negatively and densities of YOY perch were on average higher in control lakes than in treatment lakes. In years when perch recruitment did not differ between lakes as a result of experimental addition of perch eggs, total zooplankton biomass was lower in treatment lakes than in control lakes. Phytoplankton biomass showed a tendency to increase in roach lakes compared to control lakes. Within treatment variation in response variables was related to differences in lake morphometry in treatment lakes. Analyses of the trophic dynamics of each lake separately showed strong cascading effects of both roach and YOY perch abundance on zooplankton and phytoplankton dynamics. Consideration of the long transients in the dynamics of top predators (fish) in aquatic systems that are related to their long life span involving ontogenetic niche shifts is essential for making relevant interpretations of experimental perturbations. This conclusion is further reinforced by the circumstance that the intrinsic dynamics of fish populations may in many cases involve high amplitude dynamics with long time lags.     

Resource partitioning between pelagic coregonids in a subarctic watercourse following a biological invasion

If a pelagic ecosystem is invaded by an efficient planktivorous fish, competition theory predicts that habitat and/or diet segregation should occur if the invader and native planktivores are to co-exist. We compared the diet and pelagic habitat use between invading vendace (Coregonus albula) and two native morphs of whitefish (Coregonus lavaretus) in three subarctic lakes located within the same watercourse. No clear vertical habitat segregation was found as vendace prevailed throughout the entire depth range. Zooplankton generally dominated the diet of all three coregonids. No obvious resource partitioning was found in two of the lakes, while in the third lake the diets of whitefish and vendace differed significantly from each other. Here, the predominant pelagic whitefish morph fed extensively on water mites whereas vendace mainly consumed surface insects and to some extent small fish, apparently as a result of highly depleted zooplankton resources. The results suggest that various levels of resource depletion following the vendace invasion caused the observed differences between the lakes, indicating that different levels of resource partitioning were associated with dissimilar competition intensities. At present, coexistence of these congeneric species seems to be possible, although the vendace invasion has apparently resulted in a challenging and unstable situation for the planktivorous whitefish.     

Correlations between type‐indicator fish species and lake productivity in German lowland lakes

Morphotypes for 67 lakes in the German lowlands were derived, based on maximum depth and mixis type. A threshold of 11 m maximum depth was identified to be the best level to discriminate shallow from deep lake morphotypes. The fish communities in these two morphotypes were significantly different. Indicator species analyses based on fish biomasses found vendace Coregonus albula in deep lakes and ruffe Gymnocephalus cernuus , bream Abramis brama , white bream Abramis bjoerkna , roach Rutilus rutilus , pikeperch Sander lucioperca and small perch Perca fluviatilis in shallow lakes to be the most representative species of their communities. Lake productivity was closely related to biomass and in part abundance of the type‐indicator species, with vendace declining with increasing chlorophyll a concentration in the deep lakes, whereas biomass of pikeperch, bream, white bream and ruffe increased and biomass of small perch decreased with increasing chlorophyll a . These results indicate that assessment of ecological integrity of lakes by their fish fauna is generally possible, if lakes are initially separated according to a depth‐related morphotype before the assessment, and if eutrophication is considered to be the main anthropogenic degradation.     

Crayfish in lakes and streams: individual and population responses to predation, productivity and substratum availability

1. In a correlative study, we investigated the relative importance of fish predation, refuge availability and resource supply in determining the abundance and size distributions of the introduced and omnivorous signal crayfish (Pacifastacus leniusculus) in lakes and streams. Moreover, the biomass and food selection of predatory fish was estimated in each habitat type and stable isotopes of carbon and nitrogen were measured in perch (Perca fluviatilis), the dominant predator in the lakes, and in its potential food sources (crayfish, juvenile roach and isopods). 2. In lakes, crayfish were the most frequent prey in large perch (46%), followed by other macroinvertebrates (26%, including the isopod Asellus aquaticus) and small fish (25%). Crayfish and fish dominated the gut contents of large perch with respect to biomass. Nitrogen signatures showed that perch were one trophic level above crayfish (approx. 3.4‰) and a two‐source mixing model using nitrogen isotope values indicated that crayfish (81%) contributed significantly more to perch isotope values than did juvenile roach (19%). A positive correlation was found between the abundance of crayfish and the biomass of large perch. Crayfish abundance in lakes was also positively correlated with the proportion of cobbles in the littoral zone. Lake productivity (chlorophyll a) was positively correlated with crayfish size, but not with crayfish abundance. 3. In streams, brown trout (Salmo trutta) were the most abundant predatory fish. Gut contents of large trout in a forested stream showed that terrestrial insects were the most frequently found prey (60%), followed by small crayfish (27%) and isopods (27%). In contrast to lakes, the relative abundance of crayfish was negatively correlated with the total biomass of predatory fish and with total biomass of trout. However, abundance of crayfish at sites with a low biomass of predatory fish varied considerably and was related to substratum grain size, with fewer crayfish being caught when the substratum was sandy or dominated by large boulders. The mean size of crayfish was greater at stream sites with a high standing stock of periphyton, but neither predator biomass nor substratum grain size was correlated with crayfish size. 4. Our results suggest that bottom‐up processes influence crayfish size in lakes and streams independent of predator biomass and substratum availability. However, bottom‐up processes do not influence crayfish abundance. Instead, substratum availability (lakes) and interactions between predation and substratum grain size (streams) need to be considered in order to predict crayfish abundance.     

State-dependent invasion windows for prey in size-structured predator-prey systems: whole lake experiments

1. In size-structured communities where individuals grow in size over their life cycle, interactions between species will shift between competitive and predatory interactions depending on size relationships. The outcome of interactions will subsequently depend on the strength of competitive and predatory interactions, respectively. 2. In a whole lake experiment including four experimental lakes, it was tested under which conditions the competing prey, roach Rutilus rutilus, could successfully recruit into systems previously occupied by the predator, perch Perca fluviatilis. Two replicated introduction experiments were carried out 3 years apart. 3. Roach were able to successfully recruit into three of the four experimental lakes of which two were also inhabited by the top predator pike Esox lucius. Resource levels were unrelated to whether roach could successfully recruit into the systems as recruiting roach in all years were feeding close to their maximum rate. 4. High population fecundity of roach and low predation pressure by perch combined were necessary ingredients for successful recruitment and the presence of only one of these conditions did not result in successful recruitment. 5. It is hypothesized that, although roach were able to successfully recruit into one lake with only perch present in addition to the two lakes that also inhabited pike, long-term coexistence of roach and perch depends on the presence of another top predator (e.g. pike) selectively preying on perch. This hypothesis was supported by data on co-occurrence of perch and roach in different lakes. 6. Overall, the results are in accordance with expectation of size-structured life-history omnivory theory suggesting that coexistence between top predator and intermediate consumer is fragile.     

Diet-dependent body morphology and ontogenetic reaction norms in Eurasian perch

Individual morphology and performance are directly or indirectly under the influence of variation in resource levels. To study the effects of different resource conditions and their effects on morphology and ontogenetic reaction norms in young‐of‐the‐year (YOY) perch (Perca fluviatilis), we used three different approaches. First, we examined the morphological trajectories over early ontogeny in relation to lake‐specific resources in a field study. Second, one lake that lacked perch recruitment was stocked with perch eggs from a control lake in a whole‐lake experiment to study ontogenetic reaction norms. Third, we compared the development of YOY perch in the three lakes that mainly inhabited the littoral zone with YOY perch experimentally confined to enclosures in the pelagic zone of the lakes.
Overall body morphology of the YOY perch changed both as a function of size and as a function of diet. As perch increased in size they developed a deeper body morphology corresponding to an increased proportion of benthic macroinvertebrates in their diet. In pelagic enclosures where perch were constrained to feed mainly on zooplankton they had a more fusiform body morphology than perch in the lakes that fed on a mixture of zooplankton and macroinvertebrates. Similarly, the ontogenetic reaction norm of perch was related to the diet and lake‐specific zooplankton levels in the whole‐lake experiment.
In the pelagic enclosures, perch with high growth rates had a more fusiform body morphology than slow‐growing perch, whereas the opposite was found in the lakes, where perch included more macroinvertebrates in their diets. Perch in lakes with a higher proportion of macroinvertebrates in the diet also had deeper body morphology. The opposite morphology – growth rate relationship found between perch in the pelagic versus those using the whole lake suggest a morphological trade‐off between foraging on zooplankton and foraging on macroinvertebrates. Our results suggest that YOY perch show different ontogenetic reaction norms as a function of lake‐specific resource levels, which may allow YOY recruitment to later stages. Our results further suggest that diet‐related changes in morphology are a rapid process.     

Indirect trophic interactions with an invasive species affect phenotypic divergence in a top consumer

While phenotypic responses to direct species interactions are well studied, we know little about the consequences of indirect interactions for phenotypic divergence. In this study we used lakes with and without the zebra mussel to investigate effects of indirect trophic interactions on phenotypic divergence between littoral and pelagic perch. We found a greater phenotypic divergence between littoral and pelagic individuals in lakes with zebra mussels and propose a mussel-mediated increase in pelagic and benthic resource availability as a major factor underlying this divergence. Lakes with zebra mussels contained higher densities of large plankton taxa and large invertebrates. We suggest that this augmented resource availability improved perch foraging opportunities in both the littoral and pelagic zones. Perch in both habitats could hence express a more specialized foraging morphology, leading to an increased divergence of perch forms in lakes with zebra mussels. As perch do not prey on mussels directly, we conclude that the increased divergence results from indirect interactions with the mussels. Our results hence suggest that species at lower food web levels can indirectly affect phenotypic divergence in species at the top of the food chain.     

Chernobyl-derived radiocaesium in fish as dependent on water quality and lake morphometry

¹³⁷Cs concentrations in perch Perca fluviatilis , pike Esox lucius and roach Rutilus rutilus obtained from lakes of different size and water quality in an area which received about 10–67 kBq m⁻²¹³⁷Cs, were compared with environmental data. Radiocaesium concentrations were highest in pike, and were about two to three times higher in the pike and perch than in the roach. The largest perch had about four times more ¹³⁷Cs than the smallest ones, but the activities in the pike and roach were independent of fish size. All of the water quality parameters examined correlated with ¹³⁷Cs concentrations in the fish, but the concentrations of ¹³⁷Cs in the bottom sediment did not. ^l37Cs fallout and water retention time in lakes showed a positive correlation with fish ¹³⁷Cs, while the size of the catchment area, phosphorus content of the water, water colour, pH and electrical conductivity showed a negative one. Thus there was more ¹³⁷Cs in the fish from the oligotrophic lakes than from the eutrophic ones, from the less humic lakes than from the more humic ones, from the more acid than from the less acid ones and from the lakes containing less potassium than from those containing more potassium. The depth, area and volume of the lake did not affect radiocaesium in the fish. Regression equations are presented for predicting ¹³⁷Cs in fish on the basis of environmental data. Fallout, total phosphorus and pH together had the highest influence in multiple regression models but were less significant in the roach than in the perch and pike.     

Asymmetrical habitat coupling of an aquatic predator—The importance of individual specialization

Predators should stabilize food webs because they can move between spatially separate habitats. However, predators adapted to forage on local resources may have a reduced ability to couple habitats. Here, we show clear asymmetry in the ability to couple habitats by Eurasian perch—a common polymorphic predator in European lakes. We sampled perch from two spatially separate habitats—pelagic and littoral zones—in Lake Erken, Sweden. Littoral perch showed stronger individual specialization, but they also used resources from the pelagic zone, indicating their ability to couple habitats. In contrast, pelagic perch showed weaker individual specialization but near complete reliance on pelagic resources, indicating their preference to one habitat. This asymmetry in the habitat coupling ability of perch challenges the expectation that, in general, predators should stabilize spatially separated food webs. Our results suggest that habitat coupling might be constrained by morphological adaptations, which in this case were not related to genetic differentiation but were more likely related to differences in individual specialization.     

Spatial distribution of four freshwater fish species in different types of artificial European water bodies

Spatial distribution of young-of-the-year (YOY) and older roach, rudd, perch and ruffe was compared in two artificial lakes with macrophytes present and absent, and a valley reservoir, using gillnets. Almost all species of interest and both age categories preferred benthic habitats. The depth distribution in benthic habitats was relatively consistent across water bodies with the highest fish densities found in the shallowest depths. In the macrophyte-rich lake, YOY roach and perch utilize the 3–6 m benthic layer the most, whereas the fish preferred the 0–3 m benthic layer in the macrophyte-poor lake and reservoir. No differences were found in the depth distribution in pelagic habitats sampled by pelagic gillnets for YOY fish between the water bodies. Older fish usually utilized the surface water layer. Macrophytes influenced the depth distribution of YOY fish in benthic habitats, where their density maximum shifted deeper in the macrophyte-rich lake when fewer macrophytes were present in the shallowest benthic depth. In lakes, YOY fish utilized a wider depth spectrum due to the deeper thermocline when compared to the reservoir. Oxygen and temperature stratification are the main factors influencing fish distribution, whereas macrophyte presence particularly influences the depth distribution of YOY fish in benthic habitats.