Maintenance of the shore-level size gradient in the marine snail Tegula funebralis (A. Adams): Importance of behavioral responses to light and sea star predators

The intertidal gastropod, Tegula funebralis (A. Adams) exhibits a shore-level size gradient with mean shell size increasing in a down-shore direction. Snails transferred to zones where they do not usually occur migrated back towards their original zone, thus re-establishing a size gradient and implying differential movement among size classes. Both large (≥2.1 cm shell width) and small (≤ 1.77 cm) snails were photonegative on a horizontal surface and geonegative in the laboratory; there were no statistical differences between size classes. Light, however, inhibited upward, or caused downward, movement of large snails on vertical surfaces. Small snails were unaffected, ranging higher on illuminated vertical surfaces than large snails. Both sizes exhibited similar distributions in the dark. In an experimental chamber providing both emersed and immersed surfaces, T. funebralis established vertical size gradients when the chamber was illuminated from above. It is suggested that light is an important factor in the formation and maintenance of Tegula's shore-level size gradient.In response to water-borne chemicals derived from the sea star Pisaster ochraceus (Brandt), large snails moved up vertical surfaces in greater proportion than small. In response to contact with the predator, large snails moved away faster than small and individuals collected from crevices in the field moved away slower than those collected from open rock faces. Although predation may select for a size gradient in Tegulafunebralis, it is unlikely that responses to predatory sea stars directly and proximally cause or maintain them over the short term.     

Assessing the role of vertical leaves within the photosynthetic function of Styrax camporum under drought conditions

Previous evidence has demonstrated that vertical leaves of Styrax camporum, a woody shrub from the Brazilian savanna, have a higher net photosynthetic rate (P _N) compared with horizontal leaves, and that it is detected only if gas exchange is measured with light interception by both leaf surfaces. In the present study, leaf temperature (T _leaf), gas exchange and chlorophyll (Chl) a fluorescence with light interception on adaxial and also on abaxial surfaces of vertical and horizontal mature fully-expanded leaves subjected to water deficit (WD) were measured. Similar gas-exchange and fluorescence values were found when the leaves were measured with light interception on the respective surfaces of horizontal and vertical leaves. WD reduced P _N values measured with light interception on leaf surfaces of both leaf types, but the effective quantum yield of PSII (Φ_PSII) and the apparent electron transport rate (ETR) were reduced only when the leaves were measured with light interception on the adaxial surface. WD did not decrease the maximum quantum yield of PSII (F_v/F_m) or increase T _leaf, even at the peak of WD stress. Vertical leaf orientation in S. camporum is not related to leaf heat avoidance. In addition, the similar P _N values and the lack of higher values of Φ_PSII and ETR in vertical compared with horizontal leaves measured with light interception by each of the leaf surfaces suggests that the vertical leaf position is not related to photoprotection in this species, even when subjected to drought conditions. The exclusion of this photoprotective role could raise the alternative hypothesis that diverse leaf angles sustain whole plant light interception efficiency increased in this species.     

Egg Placement by Anopheles gambiae (Diptera:Culicidae) as Influenced by Resting Surface Slope and Enclosure

In these experiments, oviposition by laboratory-reared Anopheles gambiae s.s. was as likely to occur from a vertical perch, as from a horizontal sitting position on a substrate of moist mud or open water. Tall cylinders with moist, dark walls provided an enclosed vertical resting surface from which An. gambiae deposited eggs. Similar numbers of eggs were deposited in these cylinders as on dark and moist horizontally-positioned ovipositional substrates. Likewise, An. gambiae oviposited equally from a vertical perch among emergent surrogate reeds vs. sitting horizontally on mud. Open ovipositional resources with exposed resting surfaces presenting 45°, 90°, and 135° angles relative to the cage floor received fewer eggs than a horizontally positioned, moist and dark ovipositional dish, even though more An. gambiae females settled on these angled resting surfaces post-oviposition. We conclude that vertical resting sites are adequate perches from which oviposition can occur if they provide high humidity and the paramount dark and wet ovipositional cues for An. gambiae oviposition.     

Influence of light quality and gassing on the vertical migration of diatoms inhabiting the Wadden Sea

Diatoms inhabiting the Wadden Sea show a rhythmic migration pattern, which is superimposed by the tidal rhythm. In addition to light intensity, light quality has a pronounced influence on the upward-directed migration, thus giving some information on the nature of the relevant photoreceptors. Maximum diatom migration occurred when sediment surfaces were illuminated with blue light. The cell densities in blue light exceeded those of white light control experiments 1.8-fold. Furthermore, we registered a minor peak in the red light region, which reached approximately 60% of the white light controls. Cryptochrome and/or phototropin may thus be involved and act as photoreceptors for the vertical migration pattern. Flushing sediment surfaces of freshly mixed Wadden Sea sediments with air, O₂, CO₂ or N₂ did not show a significant influence of O₂ on the upward migration. The disappearance of diatoms from sediment surfaces which were flushed with CO₂ is most probably caused by the acidification of the sediment bed.Communicated by E. Rachor     

Settlement and post-settlement processes limit the abundance of the geniculate coralline alga Calliarthron on subtidal walls

Cover of geniculate coralline algae is significantly greater on subtidal platforms than on vertical walls in a central California kelp forest. To determine the cause(s) of this pattern, settlement and growth of Calliarthron were compared on horizontal and vertical substrata attached to platforms or walls. Recruitment on horizontal substrata attached to reef walls indicated that spores were abundant along the walls. Densities of recruits were significantly smaller on vertical substrata attached to walls than on horizontal substrata attached to platforms, indicating that Calliarthron settlement is reduced on vertical substrata. Growth of basal crusts and the densities of fronds were also significantly greater on horizontal substrata attached to platforms than on vertical substrata attached to walls. Irradiance reaching wall surfaces was less than irradiance reaching platform surfaces. We suggest that light reaching wall surface is low enough to affect Calliarthron growth. These results indicate that the low abundance of Calliarthron on subtidal walls is a result of poor recruitment and slow growth.     

The effects of thin layers on the vertical distribution of the rotifer, Brachionus plicatilis

Microscale patches of resources occur in both the horizontal and vertical dimensions, and in the latter case are referred to as thin layers. These layers may affect ecological processes like behavior, predation, growth and reproduction in phytoplankton and zooplankton. The objective of this study was to determine possible effects of physical and biological thin layers on the vertical distribution and diel vertical migration of the rotifer Brachionus plicatilis. We used four, 2 m tall, experimental tanks fitted with video cameras which panned the vertical extent of each tank and enabled us to sample on the centimeter scale. The experimental tanks consisted of a thin layer (25 cm thick) of Nannochloropsis oculata, whereas control tanks consisted of homogeneously distributed algae. Rotifers aggregated in the thin layers of N. oculata, and dispersed (becoming evenly distributed) after depleting the algae within the thin layer (ca. 6 h). In contrast, rotifer aggregation in the physical thin layer of control tanks was shorter in duration (ca. 2.5 h) and rotifers were homogenously distributed for the remainder of the experiment despite persistent salinity stratification. No signs of diel vertical migration were noted in either experimental or control tanks. A second set of experiments was run to examine the response of rotifers to a choice of food, i.e., thin layers of the diatom, Skeletonema costatum versus the eustigmatophyte, N. oculata. For the choice experiments, two thin layers were created, one with each food option. Our results suggest that B. plicatilis aggregates and feeds preferentially on N. oculata over S. costatum. In both types of experiments rotifers responded, in terms of distribution, to thin layers of algae within the first half-hour of introduction and remained in the thin layers until the food source was depleted. Our results suggest that rotifers may be important grazers on thin layers because of their ability to quickly locate and take advantage of ephemeral food patches.     

Feeding preference of Strongylocentrotus droebachiensis (Echinoidea) for a dominant native ascidian, Aplidium glabrum, relative to the invasive ascidian Botrylloides violaceus

Subtidal benthic communities show distinct patterns of community structure related to substrate angle. Suspension-feeding invertebrate communities often dominate vertical and undercut rock surfaces, while macroalgae dominate horizontal surfaces. One factor that may shape this pattern is sea urchin grazing, which is often more intense on horizontal surfaces. The native Gulf of Maine ascidian Aplidium glabrum, like other native ascidians, is generally restricted to vertical and undercut rock walls, whereas the introduced ascidian Botrylloides violaceous is often abundant on horizontal surfaces. We tested the hypothesis that this pattern could be due to differing predation intensity on these two ascidians by Strongylocentrotus droebachiensis, a dominant omnivore in the Gulf of Maine. Feeding preference of S. droebachiensis on the native A. glabrum vs. B. violaceous was estimated in the laboratory and in field experiments. Laboratory results show that S. droebachiensis prefers to feed on the native ascidian A. glabrum over B. violaceous. In the field, potential differences in the impact of S. droebachiensis on the two species were masked by the much greater growth rate of B. violaceus compared to A. glabrum. These results may help explain observed patterns in ascidian distribution in the Gulf of Maine, and ultimately the overall success of B. violaceus as a major invader throughout New England.     

VIIRS captures phytoplankton vertical migration in the NE Gulf of Mexico

In summer 2014, a toxic Karenia brevis bloom (red tide) occurred in the NE Gulf of Mexico, during which vertical migration of K. brevis has been observed from glider measurements. The current study shows that satellite observations from the Visible Infrared Imaging Radiometer Suite (VIIRS) can capture changes in surface reflectance and chlorophyll concentration occurring within 2 h, which may be attributed this K. brevis vertical migration. The argument is supported by earlier glider measurements in the same bloom, by the dramatic changes in the VIIRS-derived surface chlorophyll, and by the consistency between the short-term reflectance changes and those reported earlier from field-measured K. brevis vertical migration. Estimates using the quasi-analytical algorithm also indicate significant increases in both total absorption coefficient and backscattering coefficient in two hours. The two observations in a day from a single polar-orbiting satellite sensor are thus shown to be able to infer phytoplankton vertical movement within a short timeframe, a phenomenon difficult to capture with other sensors as each sensor can provide at most one observation per day, and cross-sensor inconsistency may make interpretation of merged-sensor data difficult. These findings strongly support geostationary satellite missions to study short-term bloom dynamics.     

Interactive effects of global and regional change on a coastal ecosystem

Vertical distribution and diel vertical migration of a zooplankton community were studied at two stations off Central Peru in April 2006. Zooplankton was collected at five depth strata by vertical hauls with Hydo-Bios multinet (300-μm mesh, 0.25-m² mouth size). The zooplankton community was distributed in relation to a strong, shallow oxycline (1 ml l^?1 oxygen isopleth generally above 36 m). The highest total abundance was always in the upper, well-oxygenated layer. The most important species were: Acartia tonsa (72.86%), Centropages brachiatus (7.5%), and Paracalanus parvus (3.1%); Acartia tonsa was the dominant species at all times. Larvae of the polychaete Magelona sp. (7.5%) and larvae of the brachiopod Discinisca lamellosa (3.5%) were numerically dominant in April and small copepods e.g. Oncaea venusta (3.88%) were numerically dominant during August. Five distinct patterns of vertical distribution and migration in relation to the oxygen minimum layer were distinguished in this study: (1) Ontogenetic vertical migration through the oxycline (Acartia tonsa adults, nauplii, and copepodids), (2) permanent limitation to layers above the oxycline (e.g. Oikopleura sp., most invertebrate larvae), (3) distribution mostly below the oxycline with occasional migration into the layers just above the oxycline (Eucalanus inermis), (4) Diel Vertical Migration (Centropages brachiatus), and (5) reverse Diel Vertical Migration (larvae of the polychaete Magelona sp.).     

Rho family GTPases: Making it to the third dimension

The role of Rho family GTPases in controlling the actin cytoskeleton and thereby regulating cell migration has been well studied for cells migrating on 2D surfaces. In vivo, cell migration occurs within three-dimensional matrices and along aligned collagen fibers with rather different spatial requirements. Recently, a handful of studies coupled with new approaches have demonstrated that Rho GTPases have unique regulation and roles during cell migration within 3D matrices, along collagen fibers, and in vivo. Here we propose that migration on aligned matrices facilitates spatial organization of Rho family GTPases to restrict and stabilize protrusions in the principle direction of alignment, thereby maintaining persistent migration. The result is coordinated cell movement that ultimately leads to higher rates of metastasis in vivo.     

To migrate, or not to migrate: partial diel horizontal migration of fish in a temperate freshwater reservoir

The diel horizontal migration (DHM) of fish between the inshore and offshore zones of the ?ímov Reservoir (Czech Republic, deep, stratified, meso-eutrophic) was investigated by a combination of horizontal and vertical hydroacoustic surveys at 3-h intervals over 48 h and day/night purse seining in August 2007. An overwhelming majority of fish were aggregated within the epilimnetic layer. Considering only the horizontal surveys, cyclic diel fish movements between inshore and offshore habitats were apparent, while the total fish biomass remained constant between day and night. A higher fish biomass was detected in the offshore zone during daytime by both hydroacoustics and purse seining. In contrast, a higher fish biomass was recorded at night in the inshore zone. Bream Abramis brama, roach Rutilus rutilus, and perch Perca fluviatilis dominated the daytime offshore fish assemblage whereas bleak Alburnus alburnus prevailed at night. Bream and roach decreased in abundance at night while perch completely disappeared from the offshore habitat. The diel differences in size distributions and direct catches suggested the population-wide horizontal offshore migration of bleak and inshore migration of all perch during dusk. On the other hand, partial inshore migration of bream and roach adults was observed during dusk (52 and 80%, respectively). The different proportions of offshore residents among species and size classes suggested that differences in size, and, therefore, predation vulnerability, contributed to the observed migration patterns.     

Effect of Soil Texture and the Clay Component on Migration of Meloidogyne incognita Second-stage Juveniles

The vertical migration of M. incognita juveniles introduced at 20 cm from the roots was studied in five natural soils, 100% silica sand, 95% silica sand with 5% clay, 90% silica sand with 10% clay, and 95% silica sand with 5% clay as a concentrated layer. In natural soils the percentage of juveniles capable of migrating 20 cm and penetrating the roots decreased when the percentage of clay and silt increased. No migration occurred in silica sand without clay particles; when 5 or 10% of clay were mixed to silica sand, 34 and 26%, respectively, of the juveniles were able to migrate 20 cm. Clay separated from silica sand in which tomatoes were grown was attractive for juveniles. It is suggested that clay particles aid in the migration of root-knot juveniles over long distances to plant roots by absorbing and holding root exudates or bacterial by-products which form a concentration gradient enabling nematodes to locate roots.     

Highly Ordered Vertical Structure of Synechococcus Populations within the One-Millimeter-Thick Photic Zone of a Hot Spring Cyanobacterial Mat

A variety of contemporary techniques were used to investigate the vertical distribution of thermophilic unicellular cyanobacteria, Synechococcus spp., and their activity within the upper 1-mm-thick photic zone of the mat community found in an alkaline siliceous hot spring in Yellowstone National Park in Wyoming. Detailed measurements were made over a diel cycle at a 61°C site. Net oxygenic photosynthesis measured with oxygen microelectrodes was highest within the uppermost 100- to 200-μm-thick layer until midmorning, but as the day progressed, the peak of net activity shifted to deeper layers, stabilizing at a depth of 300 μm from midday throughout the afternoon. Examination of vertical thin sections by bright-field and autofluorescence microscopy revealed the existence of different populations of Synechococcus which form discrete bands at different vertical positions. Denaturing gradient gel electrophoresis analysis of PCR-amplified 16S rRNA gene segments from horizontal cryosections obtained at 100-μm-thick vertical intervals also suggested vertical stratification of cyanobacterial, green sulfur bacterium-like, and green nonsulfur bacterium-like populations. There was no evidence of diel migration. However, image analysis of vertical thin sections revealed the presence of a narrow band of rod-shaped Synechococcus cells in which the cells assumed an upright position. These upright cells, located 400 to 800 μm below the surface, were observed only in mat samples obtained around noon. In mat samples obtained at other time points, the cells were randomly oriented throughout the mat. These combined observations reveal the existence of a highly ordered structure within the very thin photic zone of this hot spring microbial mat, consisting of morphologically similar Synechococcus populations that are likely to be differentially adapted, some co-occurring with green sulfur bacterium-like populations, and all overlying green nonsulfur bacterium-like populations.     

Living planktonic foraminifera in the Fram Strait (Arctic): absence of diel vertical migration during the midnight sun

The timing of vertical migration in planktonic foraminifera (ex. ontogenetic, diel) is still an open debate. This work aims to investigate the diel vertical migration (DVM) of Neogloboquadrina pachyderma (N. pachyderma) and Turborotalita quinqueloba (T. quinqueloba) in the Arctic during the midnight sun. N. pachyderma and T. quinqueloba dominate the total assemblage in the cold Polar Water and warmer North Atlantic Water masses, respectively. Foraminifera were collected at several depths along the Fram Strait. Afterwards sampling was performed at the same station for 24 h at continuous and discrete time intervals. Results show no evidence of planktonic foraminifera DVM since there was no significant variability in the abundance and size distribution during the 24-h collection period. This finding provides information to improve the interpretation of foraminifera in paleoclimatic works. This is especially relevant in the Fram Strait as paleoclimatic studies in this region are fundamental to investigating the history of the Atlantic water inflow into the Arctic Ocean.     

Plankton community composition and vertical migration during polar night in Kongsfjorden

The polar night in the Arctic is characterized by up to six months of darkness, low temperatures and limited food availability. Biological data on species composition and abundance during this period are scarce due to the logistical challenges posed when sampling these regions. Here, we characterize the plankton community composition during the polar night using water samplers and zooplankton net samples (50, 64, 200, 1500 μm), supplemented by acoustics (ADCPs, 300 kHz), to address a previously unresolved question–which species of zooplankton perform diel vertical migration during the polar night? The protist community (smallest plankton fraction) was mainly represented by ciliates (Strombidiida). In the larger zooplankton fractions (50, 64, 200 μm) the species composition was represented primarily by copepod nauplii and small copepods (e.g., Microcalanus spp., Pseudocalanus spp. and Oithona similis). In the largest zooplankton fraction (>1500 μm), the euphausiid, Thysanoessa inermis, was the most abundant species followed by the chaetognath Parasagitta elegans. Classical DVM was not observed throughout the darkest parts of the polar night (November–mid-January), although, subtle vertical migration patterns were detected in the acoustic data. With the occurrence of a more distinct day–night cycle (i.e., end of January), acoustical DVM signals were observed, paralleled by a classical DVM pattern in February in the largest fractions of zooplankton net samples. We suggest that Thysanoessa spp. are main responsible for the acoustical migration patterns throughout the polar night, although, chaetognaths and copepods may be co-responsible.     

Thermal variation and factors influencing vertical migration behavior in Daphnia populations

The antipredator behavior diel vertical migration (DVM), common in aquatic keystone species Daphnia, involves daily migration from warmer surface waters before dawn to cooler deeper waters after dusk. Plasticity in Daphnia DVM behavior optimizes fitness via trade-offs between growth, reproduction, and predator avoidance. Migration behavior is affected by co-varying biotic and abiotic factors, including light, predator cues, and anthropogenic stressors making it difficult to determine each factor's individual contribution to the variation in this behavior. This study aims to better understand this ecologically significant behavior in Daphnia by: (1) determining how Daphnia pulicaria thermal preferences vary within and among natural populations; (2) distinguishing the role of temperature verses depth in Daphnia vertical migration; and (3) defining how two anthropogenic stressors (copper and nickel) impact Daphnia migratory behavior.Simulated natural lake stratification were constructed in 8 L (0.5 m tall, 14.5 cm wide) water columns to monitor under controlled laboratory conditions the individual effects of temperature gradients, depth, and metal stressors on Daphnia vertical migration. Three major findings are reported. First, while no difference in thermal preference was found among the four populations studied, within lake populations variability among isolates was high. Second, decoupling temperature and depth revealed that depth was a better predictor of Daphnia migratory patterns over temperature. Third, exposure to environmentally relevant concentrations of copper or nickel inhibited classic DVM behavior. These findings revealed the high variability in thermal preference found within Daphnia populations, elucidated the individual roles that depth and temperature have on migratory behavior, and showed how copper and nickel can interfere with the natural response of Daphnia to fish predator cues. Thus contributing to the body of knowledge necessary to predict how natural populations of Daphnia will be affected by climate related changes in lake temperatures and increased presence of anthropogenic stressors.     

Responses of the limpet, Cellana grata (Gould 1859), to hypo-osmotic stress during simulated tropical, monsoon rains

Although heat stress is often cited as the dominant physical stress on tropical shores, intertidal organisms in regions with monsoonal climates are also regularly exposed to prolonged periods of heavy rainfall. Such events are predicted to have adverse physiological effects on individuals and may result in mortality. In a series of laboratory experiments, the impact of simulated monsoonal rains was investigated on the patellid limpet, Cellana grata. Sub-lethal responses in terms of body water content, body fluid osmolality and heart rate were measured in two different size cohorts maintained on horizontal and vertical substrata. Limpets were unable to achieve any effective behavioural isolation, and exposure to either simulated rainfall or diluted seawater resulted in both large and small C. grata gaining water with subsequent dilution of mantle water and haemolymph osmolalities. With increased duration of rainfall, dilution of body fluids increased with little difference between individuals on horizontal and vertical surfaces. Body fluids generally showed proportional dilution during prolonged rain, but in some individuals there was evidence for regulation of the haemolymph relative to the mantle fluid. Overall, smaller limpets were more susceptible to prolonged rainfall than large animals in terms of swelling of soft tissues and detachment and also had higher heart rates than large limpets. Both cohorts reduced heart rates with prolonged rainfall, suggesting a degree of metabolic depression, especially on horizontal surfaces. In small limpets, no difference in heart rate was found with substratum orientation, whereas large limpets had elevated heart rates on vertical as compared to horizontal substrata, when exposed to either simulated rainfall or washed with dilute seawater. This may reflect the increased energetic costs required to maintain a relatively larger body on a vertical surface under stressful conditions. Monsoonal rainfall during emersion, and subsequent dilution of seawater, therefore, have sub-lethal physiological and possible lethal effects on intertidal limpets. This influence has been largely overlooked, but coupled with the possible synergistic effects of thermal stress, monsoon rains are likely to play an important role in community dynamics on tropical shores.     

Spatial Patterns of Entomopathogenic Nematodes in Microcosms: Implications for Laboratory Experiments

Laboratory microcosms were used to: i) measure the effects of soil moisture on survival of Steinernema riobravis and ii) investigate the suitability of using microcosms to study motility and survival of these nematodes. Nematodes recovered from soil contained in petri dishes declined by more than 95% during 7 days, whereas nematodes recovered from the inner surfaces of dishes increased 35-fold. After 7 days in dishes, >20 times as many nematodes were recovered from dish surfaces than from soil. Nematodes exhibited a negative geotropism; greater numbers of nematodes were recovered from the lid surfaces than from the surfaces of dishes. Survivorship of nematodes in soil in plastic centrifuge tubes was somewhat greater than in petri dishes, and fewer nematodes ascended above the soil line in tubes than dishes. Downward migration of nematodes was inversely related to soil column diameter, possibly due to relatively unimpeded movement along container surfaces. An assay was developed by which nematodes were rinsed from the inner surfaces of centrifuge tubes into the soil. The resulting slurry was then processed on Baermann trays to recover motile nematodes. Nematode survival in soil in centrifuge tubes was higher at soil moistures between 2-4% than at lower (0.5-1.0%) and higher (4.0-12.0%) moisture levels. Survival of S. riobravis may be enhanced by quiescence induced by moisture deficits.     

Diel vertical migrations ofMeganyctiphanes norvegica in the Kattegat: Comparison of net catches and measurements with Acoustic Doppler Current Profilers

Diel vertical migration of a stable and well-defined population of Nordic krill,Meganyctiphanes norvegica (Crustacea, Euphausiacea) was investigated during eight days in August 1989, in the Läsö-Deep, East of the Danish island Läsö. Net catches with a multi-net (MOCNESS) and measurements with a moored and a shipboard Acoustic Doppler Current Profiler (ADCP) were compared. Backscattered energy as a measure for biomass gave good correlations to the dry weight ofM. norvegica and smaller zooplankton from net catches. Diel migratory patterns matched well, as determined, parallel with both methods. Migratory vertical velocity was determined with ADCP at 2–3 cm sec^?1. The potential for the use of ADCPs for biological investigation is discussed. Vertical migration was dependent on environmental parameters. The krill did not cross a temperature barrier of 14°C, although rich food sources were situated beyond it. Differences in salinity did not play a role. Currents were involved in plankton distribution. Light was an important Zeitgeber (synchronizer) and determined the density of the krill aggregations. Feeding behaviour did not interfere with the light-induced migratory pattern of Nordic krill at the Läsö-Deep.