Upstream-downstream movements of aquatic invertebrates in a Rocky Mountain stream

Simultaneous collections of drift and organisms moving either upstream or downstream in association with the substrate were made using a specially designed sampler. Samples were taken in a diel series along a transect across the study riffle of a Colorado foothills stream on six dates over an annual cycle. In addition to longitudinal movements, taxonomic composition and diel periodicity were evaluated. The insect-dominated fauna showed a net downstream displacement. Only the caddisflies Helicopsyche borealis and Hesperophylax occidentalis exhibited net upstream movement, primarily a result of low drift frequencies. The taxonomic composition of moving invertebrates differed from that of the benthos. Drift resembled downstream moving substrate-associated invertebrates in composition, but differed from that of the upstream directed fauna. Taxa collectively exhibited four types of diel patterns: 1) similar downstream (drift and substrate-associated movements) patterns, which generally differed from the upstream pattern; 2) similar benthic (upstream and downstream) patterns, which differed from that of drift; 3) aperiodic patterns; and 4) independent patterns for each type of directional movement. Analysis of size classes based on head capsule width for the mayfly Baetis tricaudatus showed significantly smaller size in stationary individuals compared with moving individuals in the population and revealed that nymphs moving during the day were smaller than those moving at night.     

Vertical distribution and substrate preference of brown trout in a littoral zone

Synopsis We studied vertical distribution, substrate preference and food choice of brown trout, Salmo trutta, from benthic gillnet catches at four littoral sampling locations in a Norwegian hydroelectric reservoir. The sampling locations had different bottom substrates; at one location the bottom substrate consisted of sand, while at the other three, substrates consisted of stones ranging 2–5 cm, 10–30 cm and 30–150 cm in diameter, respectively. Small-sized (< 160 cm) and intermediate-size (164–269 mm) brown trout were mainly caught close to the bottom (0–0.5 m above). Small-sized brown trout were caught in the highest frequency at the location with substrate consisting of 10–30 cm large stones. Intermediate-sized brown trout were also caught in highest frequency at this location, but were also caught in a high frequency at the location with sandy substrate. In contrast, the catches of large-sized ( 270 mm) brown trout did not vary with distance from the bottom or with substrate coarseness. The most important food items for the brown trout were aquatic insects, surface insects, Eurycercus lamellatus and crustacean zooplankton, mainly Daphnia longispina, Bythotrephes longimanus, and Holopedium gibberum. In accordance with the differences in vertical distribution, benthic food was more important to small than to large brown trout. We argue that small brown trout stayed close to the bottom to reduce aggressive behaviour from larger specimens, and that small brown trout were therefore more dependent on benthic food items. We also argue that the observed differences in substrate preference between the size groups of brown trout is explained by variation in access to shelter, visual isolation between individuals and benthic feeding conditions between locations.     

Effects of hydrographic variability on the spatial, seasonal and diel diving patterns of southern elephant seals in the eastern Weddell Sea

Weddell Sea hydrography and circulation is driven by influx of Circumpolar Deep Water (CDW) from the Antarctic Circumpolar Current (ACC) at its eastern margin. Entrainment and upwelling of this high-nutrient, oxygen-depleted water mass within the Weddell Gyre also supports the mesopelagic ecosystem within the gyre and the rich benthic community along the Antarctic shelf. We used Conductivity-Temperature-Depth Satellite Relay Data Loggers (CTD-SRDLs) to examine the importance of hydrographic variability, ice cover and season on the movements and diving behavior of southern elephant seals in the eastern Weddell Sea region during their overwinter feeding trips from Bouvetøya. We developed a model describing diving depth as a function of local time of day to account for diel variation in diving behavior. Seals feeding in pelagic ice-free waters during the summer months displayed clear diel variation, with daytime dives reaching 500-1500 m and night-time targeting of the subsurface temperature and salinity maxima characteristic of CDW around 150–300 meters. This pattern was especially clear in the Weddell Cold and Warm Regimes within the gyre, occurred in the ACC, but was absent at the Dronning Maud Land shelf region where seals fed benthically. Diel variation was almost absent in pelagic feeding areas covered by winter sea ice, where seals targeted deep layers around 500–700 meters. Thus, elephant seals appear to switch between feeding strategies when moving between oceanic regimes or in response to seasonal environmental conditions. While they are on the shelf, they exploit the locally-rich benthic ecosystem, while diel patterns in pelagic waters in summer are probably a response to strong vertical migration patterns within the copepod-based pelagic food web. Behavioral flexibility that permits such switching between different feeding strategies may have important consequences regarding the potential for southern elephant seals to adapt to variability or systematic changes in their environment resulting from climate change.     

Rhythmic diel movements of pandalid shrimps in the western Mediterranean continental shelf and upper slope

In marine ecosystems, information on diel rhythmic movements of species is of importance to characterize temporal changes in the community structure. In this sense, patterns of bottom trawl catches of the pandalid caridean shrimps Chlorotocus crassicornis , Plesionika gigliolii and Plesionika martia were analysed, as a proxy of the timing and duration of their presence on the seabed, close to the autumn equinox (October) and the summer solstice (June) on the continental shelf (100 m) and the upper slope (400 m). The size structure of catches was also studied for each species to assess the possible occurrence of a modulation of rhythmic movements during ontogeny. Data showed marked diel patterns of catchability on the bottom in association with light intensity cycles in both sampling seasons and depths. Chlorotocus crassicornis on the shelf showed nocturnal peaks in catches. On the slope, Pl. gigliolii showed mainly a higher catchability at dusk and dawn, whereas the catchability of Pl. martia was mainly higher during the day time. Juveniles and adults of Pl. gigliolii and Pl. martia showed ontogenetic differences in their occurrence patterns. This phenomenon is discussed by comparing the reported catchability patterns with those of some prey species that also show rhythmic behaviour in association with the day–night cycle.     

Functional morphology and mode of life of Palaeozoic leiocope ostracodes

Leiocopes differ from all other major ostracode groups (e.g. Palaeocopa. Binodicopa, Podocopa, Myodocopa) mainly in having a simple rounded/convex shape and a strong (dorsal and/or ventral) asymmetry. These morphological features are highly conservative in leiocopes through the Palaeozoic (lower Ordovician-middle Devonian). Functional morphology and facies distribution suggest that typical 'dome-like' leiocopes (e.g. aparchitids) may have lived off the bottom in relatively deep water environments, contrasting with most (inferred) benthic Palaeozoic ostracodes (e.g. heavily calcified dimorphic palaeocopes). Reversely, smaller sized and both dorsally and ventrally asymmetrical leiocopes (e.g. Ordovician jaanussoniids) are considered as possible benthic dwellers with reduced mobility on or within the substratum. □ Ostracodes, Leiocopa, Aparchitidae, Jaanussoniidae. Palaeozoic. Ordovician, Silurian, Devonian, asymmetry, functional morphology.     

Emigration and immigration can be important determinants of benthic diatom assemblages in streams

SUMMARY.

• 1 Interspecific differences in diatom abundances in stream drift (plankton), immigration, and natural benthic assemblages were compared to assess the importance of emigration and immigration in benthic diatom community dynamics. Water samples were collected throughout a 24-h period to measure diel changes in diatom drift abundances and to estimate benthic diatom emigration rates. Immigration was assessed with 24-h colonization of bare tiles.
• 2 Dissimilarity in species composition of drift, immigration, and natural substrate assemblages indicated differential emigration and immigration among diatom species.
• 3 A mathematical model indicated that reproduction by diatoms in the plankton could not account for diel drift peaks and that diel variation in drift was an informative measure of benthic diatom emigration.
• 4 Emigration and immigration of some species constituted substantial proportions of diatom abundances on natural substrata. We conclude that emigration into the drift and immigration onto substrata can be important processes that regulate benthic diatom species composition and standing crop in streams.

     

Spatial heterogeneity of spring phytoplankton in a large tropical reservoir: could mass effect homogenize the heterogeneity by species sorting?

Dredging Austrian Danube harbours becomes necessary to keep the navigation channel free from bed sediment and to insure safe navigation, especially after major floods. In most cases, the excavated substrate is deposited in the free-flowing river section in the vicinity of the mouth of a harbour. The effects of harbour dredging on the biota need to be studied to minimize possible outcomes that may endanger the ecological status of the river system in order to implement the aims of the European Water Framework Directive. This study presents the first quantitative information on the colonisation of benthic invertebrates with respect to Danube harbours. One sampling at Linz Harbour was conducted before dredging and four samplings were carried out after dredging. Four transects were documented in the affected river section. The study used an air-lift sampler and a grab sampler to investigate if and to what extent the benthic invertebrate community is disturbed. It found that the sediment dredging heavily affected the benthic invertebrates (decline of 82% of biomass), while the dumping of the material had no effects on the benthic Danube biota. As a rough estimate (conferring to a simple trend line analysis) the harbour bottom fauna would recover after 235 days.     

Diel variations in the assemblage structure and foraging ecology of larval and 0+ year juvenile fishes in a man‐made floodplain waterbody

This study investigated diel variations in zooplankton composition and abundance, and the species composition, density, size structure, feeding activity, diet composition and prey selection of larval and 0+ year juvenile fishes in the littoral of a man‐made floodplain waterbody over five 24 h periods within a 57 day period. There was a significant difference in the species composition of diurnal and nocturnal catches, with most species consistently peaking in abundance either during daylight or at night, reflecting their main activity period. There were no consistent diel patterns in assemblage structure or the abundance of some species, however, most likely, respectively, due to the phenology of fish hatching and ontogenetic shifts in diel behaviour or habitat use. There were few clear diel patterns in the diet composition or prey selection of larval and 0+ year juvenile roach Rutilus rutilus and perch Perca fluviatilis, with most taxa consistently selected or avoided irrespective of the time of day or night, and no obvious shift between planktonic and benthic food sources, but dietary overlap suggested that interspecific interactions were probably strongest at night. It is essential that sampling programmes account for the diel ecology of the target species, as diurnal surveys alone could produce inaccurate assessments of resource use. The relative lack of consistent diel patterns in this study suggests that multiple 24 h surveys are required in late spring and early summer to provide accurate assessments of 0+ year fish assemblage structure and foraging ecology.     

The Escherichia coli clamp loader can actively pry open the β-sliding clamp

Clamp loaders load ring-shaped sliding clamps onto DNA. Once loaded onto DNA, sliding clamps bind to DNA polymerases to increase the processivity of DNA synthesis. To load clamps onto DNA, an open clamp loader-clamp complex must form. An unresolved question is whether clamp loaders capture clamps that have transiently opened or whether clamp loaders bind closed clamps and actively open clamps. A simple fluorescence-based clamp opening assay was developed to address this question and to determine how ATP binding contributes to clamp opening. A direct comparison of real time binding and opening reactions revealed that the Escherichia coli γ complex binds β first and then opens the clamp. Mutation of conserved "arginine fingers" in the γ complex that interact with bound ATP decreased clamp opening activity showing that arginine fingers make an important contribution to the ATP-induced conformational changes that allow the clamp loader to pry open the clamp.     

The influence of phototrophic benthic biofilms on Cd, Cu, Ni, and Pb transport in permeable sediments

The effect of phototrophic biofilm activity on advective transport of cadmium (Cd), copper (Cu), nickel (Ni), and lead (Pb) in sandy sediments was examined using percolated columns. Cd and Ni in the effluent exhibited clear diel cycles in biofilm-containing columns, with concentrations at the end of dark periods exceeding those during illumination by up to 4.5- and 10-fold for Ni and Cd, respectively. Similar cycles were not observed for Pb or Cu. Breakthrough of the latter metals was greatly retarded and incomplete relative to Cd and Ni, and trends in biofilm treatments did not differ greatly from those in control columns. Inhibition of photosystem II by DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea) proved that diel cycles of Cd and Ni were controlled by oxygenic photosynthesis, and microsensor measurements showed that metal cycles closely matched metabolic activity-driven pH variations. The sorption edge pH for the sand/biofilm substrate followed the order Ni > Cd > Cu > Pb, and for Ni and Cd, was within the pH 7?C10 range observed in the biofilm-containing column. Adsorption dynamics over the light periods matched pH increases, but desorption during dark periods was incomplete and slower than the rate of change of pH. Over a diel cycle, desorption was less than adsorption, resulting in net binding of dissolved metals due to the biofilm metabolic activity. Extraction with selective reagents indicated that the adsorbed metals were readily exchangeable, and potentially bioavailable. Thus, phototrophic benthic biofilms can control the transport of some metals across the sand?Cwater interface, and processes in this very thin surficial layer should be considered when evaluating chemical fluxes in permeable sediments.     

Retractile processes in T lymphocyte orientation on a stimulatory substrate: morphology and dynamics

T cells of the immune system target infected and tumor cells in crowded tissues with high precision by coming into direct contact with the intended target and orienting the intracellular Golgi apparatus and the associated organelles to the area of the cell-cell contact. The mechanism of this orientation remains largely unknown. To further elucidate it we used three-dimensional microscopy of living T cells presented with an artificial substrate mimicking the target cell surface. The data indicate that long, finger-like processes emanate from the T cell surface next to the intracellular Golgi apparatus. These processes come in contact with the substrate and retract. The retraction accompanies the reorientation of the T cell body which brings the Golgi apparatus closer to the stimulatory substrate. Numerical modeling indicates that considering the forces involved the retraction of a process attached with one end to the cell body near the Golgi apparatus and with the other end to the substrate can bring the Golgi apparatus to the substrate by moving the entire cell body. The dynamic scenarios that are predicted by the quantitative model explain features of the reorientation movements that we measured but could not explain previously. We propose that retraction of the surface processes is a force-generating mechanism contributing to the functional orientation of T lymphocytes.     

Ammonium retention and whole-stream metabolism in cave streams

The influence of sampling technique on the characterization of benthic macroinvertebrate communities on boulder-cobble substrate in two shallow freshwater ponds was analysed. Sweep-net and rock-bag sampling techniques were used to collect macroinvertebrates from two ponds in Newfoundland, Canada. Abundance and diversity of macroinvertebrates were compared in relation to the nature of the substrate and the technique. The two sampling techniques provided different estimates of diversity and density of the benthos. Neither method truly represented the benthic community as neither collected all taxa and each method typically over- or under-estimated the abundance of taxa. The difficulty of interpreting such data is discussed, with special reference to the rapid assessment of water quality in biomonitoring studies.     

Trade-offs in the response of mayflies to low oxygen and fish predation

Summary We examined how mayfly larvae (Ephemeroptera,Callibaetis montanus) balance the conflicting demands of avoiding both benthic hypoxia and fish predators. Using vertical oxygen and temperature gradients typical of ice-covered lakes, we observed the behavior of mayflies in the presence and absence of fish. In the absence of fish and with adequate oxygen, mayflies spent most of the time on the bottom substrate. As benthic oxygen concentration declined, mayflies increased their activity and moved up in the water column. In the presence of fish and with adequate oxygen, mayflies spent even more time associated with the bottom substrate and reduced their activity levels. As benthic oxygen concentrations declined, mayflies increased their activity and moved up in the water column, but to a lesser extent than when fish were absent. Because of this depression in activity and reluctance to leave the bottom substrate, mayflies endured lower oxygen concentrations in the face of predation threat relative to when fish were absent. Despite this trade-off, benthic hypoxia resulted in increased mortality due to fish predation. Because benthic invertebrates vary in their ability to tolerate hypoxia and in their vulnerability to fish predators, periods of benthic hypoxia could lead to selective predation on some taxa and be an important force structuring benthic invertebrate assemblages.     

Temporal and spatial variation in the species composition of trawl samples from a demersal fish community

The temporal variation in species and size structure of the demersal fish community of a 70–150m deep open coastal locality of SW Norway was studied by multivariate analysis of bottom trawl data both from surveys and from fixed locations sampled repeatedly through 48-h periods. The trawl data were related to echo recordings from individual tows made during the 48-h experiments, Between-site variation was greater than short-term variation at single sites. Short-term variation was largely cyclical, diel variation, involving several species. Catches of the numerically dominating species, Sebastes viviparus and Trisopterus esmarki , did not follow any diel patterns. Acoustical recordings suggested that these species undertook diel vertical migrations largely within the lower 5 m of the water column. This corresponds to the vertical opening of the trawl.     

Vertical Migrations of a Deep-Sea Fish and Its Prey

It has been speculated that some deep-sea fishes can display large vertical migrations and likely doing so to explore the full suite of benthopelagic food resources, especially the pelagic organisms of the deep scattering layer (DSL). This would help explain the success of fishes residing at seamounts and the increased biodiversity found in these features of the open ocean. We combined active plus passive acoustic telemetry of blackspot seabream with in situ environmental and biological (backscattering) data collection at a seamount to verify if its behaviour is dominated by vertical movements as a response to temporal changes in environmental conditions and pelagic prey availability. We found that seabream extensively migrate up and down the water column, that these patterns are cyclic both in short-term (tidal, diel) as well as long-term (seasonal) scales, and that they partially match the availability of potential DSL prey components. Furthermore, the emerging pattern points to a more complex spatial behaviour than previously anticipated, suggesting a seasonal switch in the diel behaviour mode (benthic vs. pelagic) of seabream, which may reflect an adaptation to differences in prey availability. This study is the first to document the fine scale three-dimensional behaviour of a deep-sea fish residing at seamounts.     

Effects of Tidal and Diel Cycles on Dugong Habitat Use

ABSTRACT Quantifying the factors influencing behaviors of aquatic mammalian grazers may enhance the generic understanding of grazer ecology. We investigated diel and tidal patterns in movements of the dugong (Dugong dugon) by Global Positioning System—tracking 12 animals in 5 inshore—intertidal and 3 offshore—subtidal habitats along the coast of Queensland, Australia. We examined effects of tide height and time of day on the dugong's distance from 1) the nearest coast, 2) water >3 m deep, 3) actual water depth (bathymetry + tide ht) experienced, and 4) distribution of the directions of movements. Both tidal and diel cycles influenced dugong movement. Tracked dugongs tended to be closer to shore at high tide than at low tide and closer to shore at night than during the day. Onshore movement was more prevalent on incoming tides and in the afternoon and evening. Offshore movement was more prevalent on outgoing tides and from midnight through the morning until midday. Tidal and diel variation in water depths used by the inshore—intertidal dugongs was small, but probably underestimated, hidden by a sampling bias in the telemetry equipment. Onshore movement at high tide allowed dugongs to exploit intertidal seagrass beds. Dugongs are closer to shore in afternoons and evenings than in mornings. This behavior may be related to the avoidance of predators or watercraft. Our findings can be used to predict spatial patterns of dugongs within areas of conservation management significance and to assess, avoid, and mitigate adverse effects of anthropogenic disturbance.     

Feeding dynamics of Terebralia palustris (Gastropoda: Potamididae) from a subtropical mangrove ecosystem

Mangrove gastropods are largely recognised for their roles as benthic deposit feeders that consume macrophyte-derived detritus. However, microalgae may also make a significant contribution towards the diet of these snails. Here we provide the first report on the rates at which microphytobenthos (MPB) is consumed by Terebralia palustris, an Indo-Pacific mangrove gastropod. Although juvenile T. palustris are generally detritivorous, there is increasing evidence that their occurrence on the seaward edge of the mangrove habitat allows them to incorporate a more nutritious food source to their diets in the form of microalgae. Using an experimental approach that incorporated fluorometric techniques, we found that the feeding activity of T. palustris on MPB was not clearly related to diel and tidal cycles at the subtropical location of Kosi Bay, South Africa during two sampling occasions in February and July 2015. However, a faster ingestion rate and higher consumption/digestion efficiency were recorded during experiments carried out in July. On this sampling occasion a higher percentage consumption of the available MPB was recorded, which corresponded to a lower per-capita availability in this resource. As T. palustris is able to consume MPB at variable rates, the impact of this species on benthic primary productivity within Indo-Pacific mangroves should not be overlooked when considering its integral ecological role within these threatened habitats.     

‘Ghost’ experiments and the dissection of social learning in humans and animals

The focus of this review is the experimental techniques used to identify forms of social learning shown by humans and nonhuman animals. Specifically, the ‘ghost display’ and ‘end‐state’ conditions, which have been used to tease apart imitative and emulative learning are evaluated. In a ghost display, the movements of an apparatus are demonstrated, often through the discrete use of fishing‐line or hidden mechanisms, without a live model acting directly upon the apparatus so that the apparatus appears to be operated as if by a ‘ghostly’ agent. In an end‐state condition, an observing individual is shown the initial state of the test apparatus, the apparatus is then manipulated out‐of‐sight and then represented to the individual in its final state. The aim of the ghost display condition is to determine whether individuals are able to emulate by replicating the movements of an apparatus, or perform a task, without requiring information about the bodily movements required to do so (imitation). The end‐state condition is used to identify goal‐emulation by assessing whether the observer can replicate the steps required to solve the task without having been shown the required body actions or task movements. The responses of individuals tested with either the ghost display and/or end‐state conditions are compared to those of further individuals who have observed a full demonstration by either a human experimenter or a conspecific. The responses of a control group, to whom no information has been provided about the test apparatus or required actions, are also compared and evaluated. The efficacy of these experimental techniques employed with humans, nonhuman primates, dogs, rats and birds are discussed and evaluated. The experiments reviewed herein emphasise the need to provide ghost displays and end‐state conditions in combination, along with full live demonstrations and a no‐information control. Future research directions are proposed.     

Bird Pollination of Explosive Flowers While Foraging for Nectar and Caterpillars1

Mucuna (Fabaceae) has explosive flowers that open only if a pressure is applied on their wings and keel. The cacique Cacicus haemorrhous inserts its bill into a flower and spreading its mandibles apart it opens the flower to take nectar. This icterine bird also preys upon caterpillars of the butterfly Astraptes talus that pupates within the flowers. Foraging with use of bill movements to take nectar or insects within a flower is an adequate mechanism to open and pollinate explosive flowers. We suggest that a plausible behavioral scenario for the pollination relationship between icterines and Mucuna‐like flowers might start with the birds' searching for insects within flowers.     

Diel feeding periodicity, daily ration and vertical migration of juvenile Cape hake off the west coast of South Africa

Feeding periodicity, daily ration and vertical migration of juvenile Cape hake Merluccius capensis are investigated from midwater and bottom trawl collections taken during a 42-h period between 29 February and 2 March 1992 at a fixed position off the west coast of South Africa. Feeding of 10-20 cm hake intensified during the night when they ascended into subsurface layers to prey on recruits of anchovy Engraulis capensis. Larger hake remained close to the bottom, were partially cannibalistic and exhibited no diel feeding periodicity. M. capensis appear to migrate vertically and feed asynchronously in midwater, as individuals, and not as a population, returning to the bottom when satiated. Based upon the exponential rate of decline in stomach fullness throughout the day, the evacuation rate by hake <20 cm was estimated as 0.054 h⁻¹; 90% evacuation of anchovy prey required an estimated 43 h. Using the Elliott & Persson and Eggers methods, the daily ration was estimated as 5.51 and 4.15% of wet body weight respectively. The effect of the foraging behaviour of M. capensis on the appropriateness of acoustic sampling for estimates of their abundance is discussed.