The movements of brown trout, Salmo trutta (L.) in Loch Leven, Kinross, Scotland

Juvenile trout enter Loch Leven during autumn and winter from the nursery streams, spend their adolescent phase offshore until reaching a length of 0.30 cm, and then move to the littoral areas in early summer. There are two types of littoral area:'favourable'areas from which movement of individual fish in the summer is very restricted, and'unfavourable'areas used briefly in early summer from which movement away is pronounced. Trout are absent from the littoral areas in winter. In subsequent summers homing to previous feeding areas is characteristic of fish from'favourable'areas, with a tendency for older fish to move to the south east area of the loch. Spawning runs occur simultaneously into the main inflows, chiefly between October and December. Emigration into the outflow occurs, but is probably unimportant.     

Lake morphometry predicts the degree of habitat coupling by a mobile predator

Habitat coupling is an ecosystem process whereby semi-discontinuous habitats are connected through the movement of energy and nutrients by chemical, physical or biological processes. One oft-cited example is that of littoral–pelagic coupling in lakes. Theory has argued that such habitat coupling may be critical to food web dynamics, yet there have been few empirical studies that have quantified ecological factors that affect the degree of habitat coupling in ecosystems. Specifically, the degree to which habitat coupling occurs across important physical gradients has largely been ignored. To address this, we investigate the degree of littoral habitat coupling (i.e. the degree to which a top predator lake trout, Salvelinus namaycush, derives energy from the littoral zone) along a gradient of lake shape, where lake shape modifies the relative quantity of coupled epilimnetic benthic and pelagic habitats within each lake. Herein we demonstrate that littoral habitat coupling is intensified in simple circular lakes compared to their reticulate counterparts in seven Canadian Shield lakes. Although the more reticulate lakes had larger areas of epilimnetic benthic habitat, littoral food sources comprised 11% compared to 24% of lake trout diet in reticulate and circular lakes, respectively. This heightened interaction in circular lakes also appears to translate into increased omnivory in more circular lakes compared to reticulate lakes such that lake trout of circular lakes have a significantly lower trophic position than lake trout of reticulate lakes (F_1,5=6.71 p=0.05). These results suggest that it is the accessibility of littoral production via thermal refugia, and not the amount of littoral production, that determines the degree to which lake trout couple littoral and pelagic habitats in lakes.     

The demography of coarse wood in north temperate lakes

1. Exchange of material across habitat boundaries is a key process in riparian zones. The movement of coarse wood from lakeshore forests to the littoral zone, where it provides habitat for aquatic organisms, is not well understood. In 2003, we resampled coarse wood within the littoral zone of four lakes in Northern Wisconsin (U.S.A.), that had originally been surveyed in 1996, to quantify the spatial arrangement of littoral coarse wood and estimate input, loss and movement rates.
2. All four lakes had a clumped pattern of littoral coarse wood, and the locations of clusters were similar in both census years. Littoral coarse wood was more abundant than expected on moderate to steep slopes, on southern shorelines, and in areas with sparse residential development.
3. All four lakes had a net accumulation of coarse wood; rates of wood input ranged from 0.5 to 1.9 logs km⁻¹ year⁻¹, i.e. there was more wood in 2003 than 1996. Movement rates of tagged logs varied 14-fold among lakes, with a maximum in one lake of 42% of logs recovered in 2003 more than 20 m from their 1996 location. Median distance moved ranged from 22 to 323 m among the four lakes.
4. Areas of persistently high wood density may be keystone habitats whose presence enables the persistence of populations of certain aquatic organisms. Conservation of locations with high wood density may be important to maintain target densities of coarse wood of lakes with human development.     

Intralacustrine movements of Galaxias maculatus (Galaxiidae) and Ondontesthes microlepidotus (Atherinidae) during their early life history

Synopsis Galaxias maculatus and Odontesthes microlepidotus undertook significant habitat shifts in a small Araucanian lake during their early life history. After hatching in the littoral zone, free embryos migrate to the limnetic zone. Later, larvae return to the littoral. A third movement, littoral-limnetic, is suggested through acoustic records of fish in the limnetic zone which correspond with the growth curve of littoral sampled juveniles.     

Movement of a South American perch Percichthys trucha in a mountain Patagonian lake during spawning and prespawning periods

Movement of the South American perch Percichthys trucha (Perciformes: Percichthyidae) was studied in a set of interconnected mountain lakes in northern Patagonia. Fish were tracked using attached acoustic tags and a fixed hydrophone array over two seasons, corresponding to the spawning (1999) and prespawning periods (2000). Percichthys trucha was found to move throughout the lake system, and to use a small, shallow, connected lake as a principal spawning area. In addition, detailed behavioural information was obtained for the spawning period. Most fish spent the initial 2 weeks descending from the littoral zone to depths of 5–8 m, presumably while feeding. Fish changed depth slowly, spending several days at each depth, and moving throughout the lake. A few days prior to the full moon, there was a change in behaviour thought to be associated with spawning, where the fish moved toward the vegetated littoral areas. Marked daily behaviour also began at this time, with movement to particular near-shore locations at dusk, and return to slightly greater depths offshore at or before dawn. Study of the behaviour of P. trucha during the breeding season has highlighted the conservation significance of the main locations within the lake system.     

Interannual variability in abundance and length of young coastal cod in the subtidal zone

The year‐to‐year variability of total length and abundance of young cod Gadus morhua in the littoral zone of the Norwegian Skagerrak coast was dominant over spatial variability. The 0 year group cod was slightly larger in exposed areas than in protected areas. Contrary to expectations, the 0 year group cod was less abundant in the protected inner parts of the fjords. Although the natural variability was very large, exposed areas (the skerries) seemed to be the better area for the 0 year group cod, while for the 1 year group cod, no differences in abundance or growth could be identified indicating that they had adopted a mature pattern of movement, utilizing the entire fjord for feeding. Available habitat data indicated that the availability of shelter was a potential cause for the distributional pattern.     

Frost formation in the ecotonal zone and its role for release of nutrients

In winter, the littoral substrate of ecotonal zones along north Swedish rivers and lakes freezes. Even if the littoral is flooded at freeze-up, the ice freezes solid to the shore substrate due to low temperature combined with a gradual decrease in water level during winter. Frost conditions were studied during an 8-year period along eight littoral transects in the River Vindelälven and adjacent riverside lagoons. Heavy frost heave with formation of needle ice was observed in several places.Nutrient release was suggested to take place due to the frost process. Sediment was taken to a laboratory experiment where samples with sediment and water were kept under unfrozen and frozen conditions during six months. N (total-N) and Ca were significantly released to the water, while P (total-P) did not show any clear movement from the frozen sediment.The results indicate that frost processes in ecotonal zones are involved in the movement of nutrients between sediment and water.     

Movement of plankton through lake-stream systems

1. River plankton are often assumed to come from upstream lakes, but the factors controlling the movement of plankton between lakes and rivers into outflow streams are unclear. We tested the possibility that the physical structure of the littoral zone near the lake outlet (depth, presence of macrophytes) and diurnal differences in plankton composition at the lake surface influence the movement of plankton from the lake into the stream and determine their persistence downstream. 2. Zooplankton and phytoplankton biomass, community composition and mean body size were compared between two deep lakes without macrophytes at the lake edge and two shallow lakes with macrophytes at the lake edge. Samples were collected day and night on three dates, in the lake centre, in the littoral zone adjacent to the lake outlet, at the outlet and at two sites downstream in Algonquin Park, Ontario, Canada. 3. The morphology of lake edges clearly affects the movement of lake zooplankton into outlet streams. Outlets draining deeper littoral zones had higher zooplankton biomass than shallow littoral outlets (P < 0.0001), but these differences disappeared within 50 m downstream of the lake. There was no difference in mean zooplankton body size among lake outlets or between littoral and outlet samples. However, shallow littoral zones were dominated by cyclopoid copepods and deeper littoral zones were dominated by Bosmina longirostris. In contrast, phytoplankton biomass entering the outlet was similar to that found within the lake and did not vary with lake outlet morphology. These effects were consistent across several sampling weeks and were not affected by surface zooplankton biomass changes associated with diurnal vertical migration in the lake centre. 4. A comparison with published river zooplankton data suggests that zooplankton are rapidly eliminated from shallow outlet streams (≤1 m deep) but persist in most deeper outlet rivers (≥2 m deep). Because the depth of an outlet river determines downstream zooplankton community development, the contribution of lakes to river plankton communities may be influenced by the location of each lake within the drainage basin. These findings suggest that lake and outflow physical structure influences connection strength between spatially successive habitats.     

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%).     

A field investigation into the effects of interspecific competition on the distribution and cover of Ulothrix flacca

Ulothrix flacca is a filamentous green alga found in its greatest abundance in the littoral fringe of the rocky intertidal during the winter months. It is much less abundant below this level. This experiment was undertaken tot determine if the lower abundance below the littoral fringe is due to the effects of interspecific competition or physiological limitations. Clearing experiments were performed on the Coast of Maine, USA to eliminate competition. Belts 10 cm wide that ran from the littoral fringe downward into the eulittoral zone were cleared of all attached organisms down to bare rock. A second condition was set up in which only the brown algal canopy was removed from a 60 cm wide belt. Unaltered belts were designated as controls. Squares 0.25 m² in area were cleared in the littoral fringe and eulittoral zone. U. flacca was able to colonize the cleared areas of the eulittoral zone and reach abundances equal to those found in the unaltered control areas of the littoral fringe. This indicates that physiological limitations do not restrict the abundance of U. flacca in the eulittoral zone. However, evidence of grazing in cleared areas adjacent to high concentrations of the barnacle Semibalanus balanoides suggest that competition alone is not responsible for the limited abundance of U. flacca in the eulittoral zone. Herbivores associated with the presence of barnacles may also have an impact on the abundance of U. flacca, even during the winter months.     

Suitability of Taxodium distichum for Afforesting the Littoral Zone of the Three Gorges Reservoir

The littoral zone ecosystem of the Three Gorges Reservoir (TGR) has become significantly degraded by annual cycles of prolonged winter flooding and summer drought. For purposes of flood control and sediment management, the water level in the reservoir is lowered by 30 m during the summer monsoon season and raised again to 175 m above sea level each year at the end of the monsoon period. To explore an effective way to promote biodiversity and associated ecosystem services, we examined Taxodium distichum as a species for afforesting the littoral zone. Sapling growth variations were measured after two rounds of winter flooding. Dominant influence factors were determined by redundancy analysis. Herb community similarities between the experimental afforested areas and nearby control areas were assessed to detect the ecosystem influence of the experimental afforestation. 94.5% of saplings planted at elevations above 168 m survived. All measured growth indices (tree height, diameter at breast height, crown width and foliage density) decreased as the flood depth increased. Completely submerged saplings had a mean dieback height of -0.65 m. Greater initial foliage density led to increased tree height and stem diameter. Shannon-Wiener indices were not significantly different between plots in experimental and control areas, but the low similarity of herb communities between experimental and control areas (0.242 on average) suggested that afforestation would enrich plant community structure and improve littoral zone ecosystem stability. Because littoral zone afforestation provides several ecosystem services (habitat, carbon sink, water purification and landscaping), it is a promising revegetation model for the TGR.     

Littoral zone of Lake Ladoga: ecological state evaluation

The littoral zone of a lake is an important ecotone between terrestrial and aquatic systems. From the point of view of the lake ecosystem, much of the mineral, organic and toxic substances entering the lake from the drainage basin are transformed in the littoral zone by physical processes and biochemical pathways. The littoral zone of Lake Ladoga can be divided into three main regions: the shallow southern region, the fairly steep western and eastern shorelines, and the northern archipelago. In these regions, the communities of aquatic macrophytes, periphyton, phyto- and zooplankton and meio- and macrobenthos have been extensively studied. This paper presents numerical data on these communities, with special reference to comparisons between areas subjected to different degrees of anthropogenic loading. Most of the communities are characterized by high species diversity and spatial heterogeneity, especially among the macrophyte associations in which intensive production and decomposition takes place. Water dynamics and water exchange rate are the main abiotic factors in the formation of littoral communities. The characteristics of plant associations and bottom substrate, rather than pollution, appear as the most important factors structuring meio- and macrobenthic invertebrate communities in the littoral.     

Behavioral and trophic plasticity of juvenileTilapia mossambica in utilization of the unstable littoral habitat

Synopsis JuvenileTilapia mossambica Peters (2.5–10.0 cm standard length) in Lake Sibaya, South Africa, move daily from deep offshore waters to shallow (<0.5 m) littoral areas where they feed for several hours and then return to deep water. The timing of these movements varies in response to changing physical and biological features of the littoral environment. During this study (December 1973 – February 1976), lake level rose more than 1 m. At the start of the study, littoral areas visited by juvenileT. mossambica were free of vegetation and debris, but at higher lake levels trees and brush from the eroding shoreline were common in nearshore littoral waters. When the littoral zone was free of debris, juvenileT. mossambica visited nearshore waters only during daylight hours. After a 0.65 m rise in lake level and considerable accumulation of debris, these fish were abundant in the littoral zone only at night. This reversal can be attributed to efforts by juvenileT. mossambica to avoid their principal predator, the catfishClarias gariepinus. At low lake levelC. gariepinus ventured into the littoral only at night but at higher lake levels this predator was found within flooded vegetation during the day. When further increases in lake level flooded marginal grasslands, juvenileT. mossambica abandoned the littoral zone in favor of this newly created eulittoral habitat where potential fish predators did not occur. With the change in habitat, the diet changed from benthic detrital aggregate to periphyton. These observations suggest the importance of behavioral and throphic plasticity in the ability of tilapia to utilize unstable habitats.     

Temperature- and light-mediated predation by perch on vendace larvae

The perch foraging pattern in a Finnish lake (64) N) was crepuscular and they moved into littoral areas at dusk and returned to deeper waters by dawn. Predation on vendace larvae was guided by environmental cues, mainly temperature and light periodicity, which affected the density and foraging activity of perch in the littoral area. The availability and the vulnerability of different food categories were both responsible for the perch diet. The hypothesis that perch have a generally decisive role in the regulation of vendace larval abundance through predation at the time of high vendace larvae concentration in the littoral area was not supported. We emphasize the need to evaluate biological phenomena, such as predator–prey relationships, in the light of the relevant physical variables, and to do so within appropriate time and space scales, instead of relying on indirect estimates of the predator and prey population abundance and using their reciprocity as evidence of the interaction.     

The biogeochemical cycle of methane in the coastal zone and littoral of the Kandalaksha Bay of the White Sea

Microbiological and biogeochemical investigations of the processes of methane production (MP) and methane oxidation (MO) in the coastal waters and littoral of the Kandalaksha Bay of the White Sea were carried out. The studies were conducted in the coastal zones and in the water areas of the Kandalaksha Preserve, Moscow University White Sea Biological Station, and Zoological Institute (RAS) Biological Station in August, 1999, 2000, and 2001 and in March, 2001. The rate of CO2 assimilation in the shallow and littoral sediments was 35-27800 microg C/(dm3 day) in summer and 32.8-88.9 microg C/(dm3 day) in winter. The maximal rates of MP were observed in the littoral sediments in the zone of macrophyte decomposition, in local depressions, and in the estuary of a freshwater creak (up to 113 microl/(dm3 day)). The maximal level of MO was observed in the shallow estuarine sediments (up to 2450 microl/(dm3 day)). During the winter season, at the temperature of -0.5 to 0.5 degrees C, the MP rate in the littoral sediments was 0.02-0.3 microl/(dm3 day), while MO rate was 0.06-0.7 microl/(dm3 day). The isotopic data obtained indicate that the C(org) of the mats and of the upper sediment layers is enriched with the heavy 13C isotope by 1-4 per thousand as compared to the C(org) of the suspension, comprised on 33.5-34.3% of phytoplankton. A striking difference was found between the levels of methane emission by the typical littoral microlanscapes. In fine sediments, the average emission was 675 microl CH4/(m2 day), in the stormy discharge stretch sediments it was 1670 microl CH4/(m2 day), and under the stones and in silted pits, 1370 microl CH4/(m2 day). The calculation performed with consideration of the microlandscape areas with a high production allowed the CH4 production of 1 km2 of the littoral to be estimated as 192-300 1 CH4/(km2 day).     

The Chydorid Crustacean Alona diaphana (King), Limnetic in Lakes Awasa and Zwai,Ethiopia, with a Discussion of Littoral and Limnetic Zooplankton

Alona diaphana, a common littoral tropicopolitan cladoceran, occurs in the limnetic of two Ethiopian lakes in considerable numbers and over long periods of time. Our results are presented and the composition of limnetic and littoral zooplankton, in terms of previous records of such incursions, are discussed. The high persistent densities of A. diaphana are due to the extensive littoral areas in the lakes, where it originates, the high intrinsic rates of increase of this species, the low diversity of zooplankton, reducing competition and the low level of predation.     

Horizontal migration of zooplankton in a littoral zone of the lowland Sulejow Reservoir (Central Poland)

Horizontal migrations of zooplankton between macrophyte patches and open areas were investigated in the sparsely vegetated littoral zone of the Sulejow Reservoir in June-July 2000 and 2001, using one-litre plastic traps. Large-bodied zooplankton: daphnids and copepods generally swam towards the open water at dusk and towards submerged macrophytes at dawn. Small-bodied zooplankton (Bosmina sp., Chydorus sp.) did not show any pattern of horizontal movement. At the time of the research the phytoplankton community was dominated by eatable diatoms (Cyclotella sp.), whose biomass reached 14 mg l⁻¹. Thus, bottom-up forces (food scarcity) are not likely to be responsible for the observed zooplankton migrations. Analyses of fish stomach contents showed high contribution of large zooplankters to the food of juvenile roach (Rutilus rutilus) and perch (Perca fluviatilis) which densely inhabited the littoral zone of reservoir. High fish pressure in the littoral zone along with high density of the predatory cladoceran, Leptodora kindtii in the open water, suggest that top-down forces (predatory pressure) were responsible for the migration of large zooplankton. At dusk predatory pressure of fish fry exceeded that of L. kindtii, forcing endangered zooplankton to escape from macrophytes towards open water. The opposite situation occurred at dawn. The consequences of the relationships for both zooplankton and fish fry communities dynamics are discussed.

     

Seasonal dynamics of akinetes of Anabaena flos-aquae in the bottom sediments and water column of a small Siberian reservoir

Seasonal dynamics of akinetes of Anabaena flos-aquae (Lyngb.) Breb. was studied in the sediments and the water column in profundal and littoral zones of a small Siberian reservoir. It was hypothesized that even in a shallow mixed reservoir cyanobacterial bloom initiates in the littoral zone and only then distributes throughout the water body. Two types of akinetes have been recognized: one type ensures vegetative reproduction, and the other, survival during adverse growth conditions. Seasonal dynamics of abundance of akinetes and vegetative cells was quite the same in water column in the littoral and profundal zones. However, there were differences in the seasonal dynamics of abundance of akinetes in the bottom sediments of these two areas: in the central zone the abundance increased throughout the vegetation period, whereas in the littoral zone the abundance decreased after settling of akinetes. During winter, the abundance of akinetes decreased in the sediments in both profundal and littoral zones. The explanation to this fact has not been found yet.     

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.