The distribution of subarctic and boreal deep-sea demersal fish assemblages across environmental gradients of the northwest Atlantic.

The oceanography of the Labrador Sea is well studied because of its globally important deep-water convection that oxygenates the deep ocean and drives climate-regulating ocean currents. However, little is known about the fish communities that inhabit this area, particularly beyond the depths accessible to standard research surveys and commercial fishing activities. We used baited longline surveys to characterize important components of demersal fish communities across a depth gradient of 200-3000 m and compared these data to a similar dataset collected c. 1200 km to the south in the Flemish Cap Region. We found demersal fish communities in the Labrador Sea to be similar to those of the Flemish Cap Region despite unique oceanography and lower primary productivity in the Labrador Sea. Moreover, both areas had high abundance, biomass, and species richness at intermediate depths that suggests factors beyond depth drive community structure in the deep ocean. These data are important for identifying high-value areas for potential protective measures in the northwest Atlantic and provide necessary data with which to assess potential environmental impacts of extractive industries that are expanding north and to deeper waters.

Hydraulic tradeoffs underlie local variation in tropical forest functional diversity and sensitivity to drought.

Tropical forests are important to the regulation of climate and the maintenance of biodiversity on Earth. However, these ecosystems are threatened by climate change, as temperatures rise and droughts' frequency and duration increase. Xylem anatomical traits are an essential component in understanding and predicting forest responses to changes in water availability. We calculated the community-weighted means and variances of xylem anatomical traits of hydraulic and structural importance (plot-level trait values weighted by species abundance) to assess their linkages to local adaptation and community assembly in response to varying soil water conditions in an environmentally diverse Brazilian Atlantic Forest habitat. Scaling approaches revealed community-level tradeoffs in xylem traits not observed at the species level. Towards drier sites, xylem structural reinforcement and integration balanced against hydraulic efficiency and capacitance xylem traits, leading to changes in plant community diversity. We show how general community assembly rules are reflected in persistent fiber-parenchyma and xylem hydraulic tradeoffs. Trait variation across a moisture gradient is larger between species than within species and is realized mainly through changes in species composition and abundance, suggesting habitat specialization. Modeling efforts to predict tropical forest diversity and drought sensitivity may benefit from adding hydraulic architecture traits into the analysis.

Coral diversity matches marine park zonation but not economic value of coral reef sites at St. Eustatius, eastern Caribbean.

Stony corals play a key role in the marine biodiversity of many tropical coastal areas as suppliers of substrate, food and shelter for other reef organisms. Therefore, it is remarkable that coral diversity usually does not play a role in the planning of protected areas in coral reef areas. In the present study we examine how stony coral diversity patterns relate to marine park zonation and the economic value of reefs around St. Eustatius, a small island in the eastern Caribbean, with fisheries and tourism as important sources of income. The marine park contains two no-take reserves. A biodiversity survey was performed at 39 sites, 24 inside the reserves and 15 outside; 22 had a maximum depth >18 m and 17 were shallower. Data on economic value per site were obtained from the literature. Corals were photographed for the verification of identifications made in the field. Coral species richness (n = 49) was highest in the no-take reserves and species composition was mainly affected by maximum depth. No distinct relation is observed between coral diversity and fishery value or total economic value. Based on the outcome of this study we suggest that in future designs of marine park zonation in reef areas, coral diversity should be taken into consideration. This is best served by including reef areas with a continuous depth gradient from shallow flats to deep slopes.

Variations in Microbial Diversity and Metabolite Profiles of the Tropical Marine Sponge Xestospongia muta with Season and Depth.

Xestospongia muta is among the most emblematic sponge species inhabiting coral reefs of the Caribbean Sea. Besides being the largest sponge species growing in the Caribbean, it is also known to produce secondary metabolites. This study aimed to assess the effect of depth and season on the symbiotic bacterial dynamics and major metabolite profiles of specimens of X. muta thriving in a tropical marine biome (Portobelo Bay, Panamá), which allow us to determine whether variability patterns are similar to those reported for subtropical latitudes. The bacterial assemblages were characterized using Illumina deep-sequencing and metabolomic profiles using UHPLC-DAD-ELSD from five depths (ranging 9-28 m) across two seasons (spring and autumn). Diverse symbiotic communities, representing 24 phyla with a predominance of Proteobacteria and Chloroflexi, were found. Although several thousands of OTUs were determined, most of them belong to the rare biosphere and only 23 to a core community. There was a significant difference between the structure of the microbial communities in respect to season (autumn to spring), with a further significant difference between depths only in autumn. This was partially mirrored in the metabolome profile, where the overall metabolite composition did not differ between seasons, but a significant depth gradient was observed in autumn. At the phyla level, Cyanobacteria, Firmicutes, Actinobacteria, and Spirochaete showed a mild-moderate correlation with the metabolome profile. The metabolomic profiles were mainly characterized by known brominated polyunsaturated fatty acids. This work presents findings about the composition and dynamics of the microbial assemblages of X. muta expanding and confirming current knowledge about its remarkable diversity and geographic variability as observed in this tropical marine biome.

Marginal sinks or potential refuges? Costs and benefits for coral-obligate reef fishes at deep range margins.

Escalating climate-related disturbances and asymmetric habitat losses will increasingly result in species living in more marginal habitats. Marginal habitats may represent important refuges if individuals can acquire adequate resources to survive and reproduce. However, resources at range margins are often distributed more sparsely; therefore, increased effort to acquire resources can result in suboptimal performance and lead to marginal populations becoming non-self-sustaining sink-populations. Shifting resource availability is likely to be particularly problematic for dietary specialists. Here, we use extensive in situ behavioural observations and physiological condition measurements to examine the costs and benefits of resource-acquisition along a depth gradient in two obligate corallivore reef fishes with contrasting levels of dietary specialization. As expected, the space used to secure coral resources increased towards the lower depth margin. However, increased territory sizes resulted in equal or greater availability of resources within deeper territories. In addition, we observed decreased competition and no differences in foraging distance, pairing behaviour, body condition or fecundity at greater depths. Contrary to expectation, our results demonstrate that coral-obligate fishes can select high-quality coral patches on the deeper-reef to access equal or greater resources than their shallow-water counterparts, with no extra costs. This suggests depth offers a viable potential refuge for some at-risk coral-specialist fishes.

Ciliate diversity and distribution patterns in the sediments of a seamount and adjacent abyssal plains in the tropical Western Pacific Ocean.

BACKGROUND: Benthic ciliates and the environmental factors shaping their distribution are far from being completely understood. Likewise, deep-sea systems are amongst the least understood ecosystems on Earth. In this study, using high-throughput DNA sequencing, we investigated the diversity and community composition of benthic ciliates in different sediment layers of a seamount and an adjacent abyssal plain in the tropical Western Pacific Ocean with water depths ranging between 813 m and 4566 m. Statistical analyses were used to assess shifts in ciliate communities across vertical sediment gradients and water depth. RESULTS: Nine out of 12 ciliate classes were detected in the different sediment samples, with Litostomatea accounting for the most diverse group, followed by Plagiopylea and Oligohymenophorea. The novelty of ciliate genetic diversity was extremely high, with a mean similarity of 93.25% to previously described sequences. On a sediment depth gradient, ciliate community structure was more similar within the upper sediment layers (0-1 and 9-10 cm) compared to the lower sediment layers (19-20 and 29-30 cm) at each site. Some unknown ciliate taxa which were absent from the surface sediments were found in deeper sediments layers. On a water depth gradient, the proportion of unique OTUs was between 42.2% and 54.3%, and that of OTUs shared by all sites around 14%. However, alpha diversity of the different ciliate communities was relatively stable in the surface layers along the water depth gradient, and about 78% of the ciliate OTUs retrieved from the surface layer of the shallowest site were shared with the surface layers of sites deeper than 3800 m. Correlation analyses did not reveal any significant effects of measured environmental factors on ciliate community composition and structure. CONCLUSIONS: We revealed an obvious variation in ciliate community along a sediment depth gradient in the seamount and the adjacent abyssal plain and showed that water depth is a less important factor shaping ciliate distribution in deep-sea sediments unlike observed for benthic ciliates in shallow seafloors. Additionally, an extremely high genetic novelty of ciliate diversity was found in these habitats, which points to a hot spot for the discovery of new ciliate species.

Exploring depth-related patterns of sponge diversity and abundance in marginal reefs.

Marine sponges play a vital role in the reef's benthic community; however, understanding how their diversity and abundance vary with depth is a major challenge, especially on marginal reefs in areas deeper than 30 m. To help bridge this gap, we used underwater videos at 24 locations between 2- and 62-meter depths on a marginal reef system in the Southwestern Atlantic to investigate the effect of depth on the sponge metacommunity. Specifically, we quantified the abundance, density, and taxonomic composition of sponge communities, and decomposed their gamma (γ) diversity into alpha (α) and beta (ß) components. We also assessed whether beta diversity was driven by species replacement (turnover) or by nesting of local communities (nestedness). We identified 2020 marine sponge individuals, which belong to 36 species and 24 genera. As expected, deep areas (i.e., those greater than 30 m) presented greater sponge abundance and more than eightfold the number of sponges per square meter compared to shallow areas. About 50% of the species that occurred in shallow areas (<30 m) also occurred in deep areas. Contrarily to expectations, alpha diversity of rare (0 D α), typical (1 D α), or dominant (2 D α) species did not vary with depth, but the shallow areas had greater beta diversity than the deep ones, especially for typical (1 D ß) and dominant (2 D ß) species. Between 92.7% and 95.7% of the beta diversity was given by species turnover both inside and between shallow and deep areas. Our results support previous studies that found greater sponge abundance and density in deep areas and reveal that species sorting is stronger at smaller depths, generating more beta diversity across local communities in shallow than deep areas. Because turnover is the major driver at any depth, the entire depth gradient should be considered in management and conservation strategies.

Body size and trophic level increase with latitude, and decrease in the deep-sea and Antarctica, for marine fish species.

The functional traits of species depend both on species' evolutionary characteristics and their local environmental conditions and opportunities. The temperature-size rule (TSR), gill-oxygen limitation theory (GOLT), and temperature constraint hypothesis (TCH) have been proposed to explain the gradients of body size and trophic level of marine species. However, how functional traits vary both with latitude and depth have not been quantified at a global scale for any marine taxon. We compared the latitudinal gradients of trophic level and maximum body size of 5,619 marine fish from modelled species ranges, based on (1) three body size ranges, <30, 30-100, and >100 cm, and (2) four trophic levels, <2.20, 2.20-2.80, 2.81-3.70, >3.70. These were parsed into 5° latitudinal intervals in four depth zones: whole water column, 0-200, 201-1,000, and 1,001-6,000 m. We described the relationship between latitudinal gradients of functional traits and salinity, sea surface and near seabed temperatures, and dissolved oxygen. We found mean body sizes and mean trophic levels of marine fish were smaller and lower in the warmer latitudes, and larger and higher respectively in the high latitudes except for the Southern Ocean (Antarctica). Fish species with trophic levels ≤2.80 were dominant in warmer and absent in colder environments. We attribute these differences in body size and trophic level between polar regions to the greater environmental heterogeneity of the Arctic compared to Antarctica. We suggest that fish species' mean maximum body size declined with depth because of decreased dissolved oxygen. These results support the TSR, GOLT and TCH hypotheses respectively. Thus, at the global scale, temperature and oxygen are primary factors affecting marine fishes' biogeography and biological traits.

Soil microbial abundance was more affected by soil depth than the altitude in peatlands.

Soil microbial abundance is a key factor to predict soil organic carbon dynamics in peatlands. However, little is known about the effects of altitude and soil depth and their interaction on soil microbial abundance in peatlands. In this study, we measured the microbial abundance and soil physicochemical properties at different soil depths (0-30 cm) in peatlands along an altitudinal gradient (from 200 to 1,500 m) on Changbai Mountain, China. The effect of soil depth on soil microbial abundance was stronger than the altitude. The total microbial abundance and different microbial groups showed the same trend along the soil depth and altitudinal gradients, respectively. Microbial abundance in soil layer of 5-10 cm was the highest and then decreased with soil depth; microbial abundance at the altitude of 500-800 m was the highest. Abiotic and biotic factors together drove the change in microbial abundance. Physical variables (soil water content and pH) and microbial co-occurrence network had negative effects on microbial abundance, and nutrient variables (total nitrogen and total phosphorus) had positive effects on microbial abundance. Our results demonstrated that soil depth had more effects on peatland microbial abundance than altitude. Soil environmental change with peat depth may lead to the microorganisms receiving more disturbances in future climate change.

The response mechanism of Hydrilla verticillata and leaf epiphytic biofilms to depth and nutrient removal.

The mechanism of morphological and physiological regulation of submerged aquatic plants (Hydrilla verticillata) is influenced by spatial and environmental changes related to water depth gradients. In the present study, changes in the aquatic microcosm were explored at the depth gradients of 0.3 m, 0.6 m, 0.9 m, 1.2 m, and 1.5 m, and the depth was recognized as a critical factor for improving water quality, especially for the removal of total phosphorus (TP) and recalcitrant protein-like molecules. At 0.9 m, the removal rates of TP and protein-like substances reached 78% and 18.67%, respectively, 1.76 times and 1.28 times the rates at 0.3 m. The maximum shoot/root growth and chlorophyll (a + b) suggest photosynthesis inhibition is minimal at 1.2 m. Fluctuations in enzyme activities imply an antioxidant response to lipid peroxidation damage under different oxidative stress. The adjusted activities of glutamine synthetase (GS) and alkaline phosphatase (APA) were an adaptive nutrient utilization strategy to different water depths. Microbiological diversity analysis of biofilms indicates that community structure changes in response to water depth. Considering the growth status and nutrient removal effects, the results indicate that the optimal planting depth for H. verticillata is 0.9-1.2 m. These findings contribute to understanding water purification mechanisms in depth gradients, and support the effective rebuilding and management of submerged macrophyte communities in natural shallow lakes.

High functional diversity in deep-sea fish communities and increasing intraspecific trait variation with increasing latitude.

Variation in both inter- and intraspecific traits affects community dynamics, yet we know little regarding the relative importance of external environmental filters versus internal biotic interactions that shape the functional space of communities along broad-scale environmental gradients, such as latitude, elevation, or depth. We examined changes in several key aspects of functional alpha diversity for marine fishes along depth and latitude gradients by quantifying intra- and interspecific richness, dispersion, and regularity in functional trait space. We derived eight functional traits related to food acquisition and locomotion and calculated seven complementary indices of functional diversity for 144 species of marine ray-finned fishes along large-scale depth (50-1200 m) and latitudinal gradients (29°-51° S) in New Zealand waters. Traits were derived from morphological measurements taken directly from footage obtained using Baited Remote Underwater Stereo-Video systems and museum specimens. We partitioned functional variation into intra- and interspecific components for the first time using a PERMANOVA approach. We also implemented two tree-based diversity metrics in a functional distance-based context for the first time: namely, the variance in pairwise functional distance and the variance in nearest neighbor distance. Functional alpha diversity increased with increasing depth and decreased with increasing latitude. More specifically, the dispersion and mean nearest neighbor distances among species in trait space and intraspecific trait variability all increased with depth, whereas functional hypervolume (richness) was stable across depth. In contrast, functional hypervolume, dispersion, and regularity indices all decreased with increasing latitude; however, intraspecific trait variation increased with latitude, suggesting that intraspecific trait variability becomes increasingly important at higher latitudes. These results suggest that competition within and among species are key processes shaping functional multidimensional space for fishes in the deep sea. Increasing morphological dissimilarity with increasing depth may facilitate niche partitioning to promote coexistence, whereas abiotic filtering may be the dominant process structuring communities with increasing latitude.

Diversity of deep-water coral-associated bacteria and comparison across depth gradients.

Environmental conditions influence species composition, including the microbial communities that associate with benthic organisms such as corals. In this study we identified and compared bacteria that associate with three common deep-water corals, Lophelia pertusa, Madrepora oculata and Paragorgia arborea, from a reef habitat on the mid-Norwegian shelf. The 16S rRNA gene amplicon sequencing data obtained revealed that >50% of sequences were represented by only five operational taxonomic units. Three were host-specific and unclassified below class level, belonging to Alphaproteobacteria with affiliation to members of the Rhizobiales order (L. pertusa), Flavobacteria affiliated with members of the Elisabethkingia genus (M. oculata) and Mollicutes sequences affiliated with the Mycoplasma genus (P. arborea). In addition, gammaproteobacterial sequences within the genera Sulfitobacter and Oleispira were found across all three deep-water coral taxa. Although highly abundant in the coral microbiomes, these sequences accounted for <0.1% of the surrounding bacterioplankton, supporting specific relationships. We combined this information with previous studies, undertaking a meta-data analysis of 165 widespread samples across coral hosts and habitats. Patterns in bacterial diversity indicated enrichment of distinct uncultured species in coral microbiomes that differed among deep (>200 m), mesophotic (30-200 m) and shallow (<30 m) reefs.

Vertical distribution of benthic diatoms in a large reservoir (Alqueva, Southern Portugal) during thermal stratification.

Freshwater diatom communities are known to respond to a wide range of environmental factors, however, the depth gradient is usually neglected and few studies are available, especially in large reservoirs. During the ALqueva hydro-meteorological EXperiment (ALEX) field campaign, diatom communities were studied in the margins and in three platforms (from the surface to the bottom of the reservoir) located in the limnetic zone of the Alqueva reservoir, one of the largest artificial lakes in western Europe. A detailed meteorological and physico-chemical characterization of the reservoir was carried out from June to September in Summer 2014, when the reservoir was stratified, to relate these variables with diatom assemblages. Despite the large dimensions of the reservoir, no differences in the water physico-chemical characteristics and diatom descriptors were detected among platforms. Small changes in diatom assemblages, ecological guilds, taxa richness and Shannon diversity index were observed between sampling campaigns. Nevertheless, differences in diatoms were detected along a depth gradient, both in terms of diatom assemblages and ecological guilds. Taxa richness, Shannon diversity index, Pielou's evenness and Specific Pollution sensitivity Index (SPI) also differed with depth, with the lowest values of all indices detected at surface samples, increasing with depth, reaching the highest values at 20 m for taxa richness, Shannon diversity and Pielou's evenness indices.

Trends of Microdiversity Reveal Depth-Dependent Evolutionary Strategies of Viruses in the Mediterranean.

The evolutionary interactions between viruses and their prokaryotic hosts remain a little-known aspect of microbial evolution. Most studies on this topic were carried out in pure cultures that challenge one virus with one bacterial clone at a time, which is very removed from real-life situations. Few studies have addressed trends of microdiversity in marine viral communities throughout depth gradients. We analyzed metagenomes from both the cellular and viral fractions of Mediterranean seawater samples spanning the epipelagic to the bathypelagic zones at depths of 15, 45, 60, and 2,000 m during the summer stratification of the water column. We evaluated microdiversity patterns by measuring the accumulation of synonymous and nonsynonymous mutations in viral genes. Our results demonstrated clear depth-dependent trends in the frequency of polymorphic sites and nonsynonymous mutations among genes encoding metabolic, structural, and replication proteins. These differences were linked to changes in energy availability, host and viral densities, and the proportions of actively replicating viruses. We propose the hypothesis that in the energy-rich, high-host-density, euphotic depths, selection acts to favor diversity of the host recognition machinery to increase host range, while in energy-depleted aphotic waters, selection acts on viral replication fitness, enhancing diversity in auxiliary metabolic genes.IMPORTANCE Viruses are extremely abundant and diverse biological entities that contribute to the functioning of marine ecosystems. Despite their recognized importance, few studies have addressed trends of mutation accumulation in marine viral communities across depth gradients. By investigating these trends, we show that mutation frequencies differ among viral genes according to their molecular functions, with the highest microdiversity occurring among proteins related to host metabolism, followed by structural proteins and, lastly, genome replication proteins. This is in agreement with evolutionary theory that postulates that housekeeping genes are under strong purifying selection. We also observed a positive association between depth and microdiversity. One exception to this trend was the host recognition proteins from the deep chlorophyll maximum, which displayed strikingly high microdiversity, which we hypothesize to be associated with intraspecies competition for hosts. Finally, our data allowed us to propose a theoretical model for viral microdiversity across the depth gradient. These discoveries are of special relevance because many of the viral genomic sequences discovered here were predicted to infect some of the most abundant bacteria in marine ecosystems, such as "Candidatus Pelagibacter," Puniceispirillum, and Prochlorococcus.

Plasticity in Sexual Dimorphism Enhances Adaptation of Dioecious Vallisneria natans Plants to Water Depth Change.

Sexual dimorphism in vegetative and reproductive traits is associated with contrasting strategies of males and females for response to varied environmental conditions, causing sex-specific reproduction success and consequently long-distance dispersal and colonization. Aquatic plants usually exhibit rich phenotypic plasticity and great diversity in reproductive systems, but the influence of aquatic conditions on the plasticity of sexual dimorphism has received less attention. Using a common garden experiment with dioecious submerged plant Vallisneria natans grown at various water depths simulating different light availability, we measured variations in 20 traits for females and 19 traits for males (total = 540 plants from 30 seed families) including morphology, reproductive traits and photosynthesis. We investigated sex-specific plastic responses and variation of sexual dimorphism in response to water depth change. Females displayed much greater leaf length, vegetative biomass and resource allocation to reproduction than males at all depths, whereas spathe number and gamete production per spathe displayed reverse pattern. Besides most traits in each sex (16 in female and 12 in male) showing striking phenotypic plasticity, the degree of sexual dimorphism increased significantly for total biomass and reproductive investment, but decreased for leaf length, spathe number and flowering ramet percentage in low light and deep water. Females varied more than males in leaf length, total biomass, reproductive investment, length and biomass of reproductive organs and rate of photosynthesis in response to decreased underwater light availability, suggesting that female has greater plasticity than male. These findings illustrated considerable plasticity in the degree of sexual dimorphism in a variety of vegetative and reproductive traits across different environments driven by the contrasting reproductive functions of the sexes in relation to pollen and seed dispersal. Females of V. natans responded more plastically than males to low light conditions resulted from water depth variation in either aboveground vegetative growth or reproduction. This study provides novel insight into adaptive strategies of submerged dioecious macrophytes to survive and increase fitness in freshwater habitats.

Benthic ciliate diversity and community composition along water depth gradients: a comparison between the intertidal and offshore areas.

The diversity of marine benthic ciliates is largely known from the intertidal zone. No comparative data are available for the change of ciliate communities from the intertidal to offshore sediments in the Yellow Sea. We investigated the community composition and diversity of benthic ciliates at two intertidal (sandy and silty-sand) stations and eight offshore stations along a latitudinal transect in the Yellow Sea. The ciliate abundance and biomass decreased almost linearly with increasing water depth and distance from the intertidal zone. Diversity indices showed a similar trend. By contrast, the total species richness and taxonomic diversity were much higher in the offshore sediments than in the intertidal area. Among the total of 94 species identified, only 20 species were shared by the two habitats, which were characterized by different dominant ciliate assemblages. Carnivorous ciliates always constituted the primary feeding type in terms of biomass at all offshore stations and the intertidal sandy station, whereas at the intertidal silty-sand station the primary feeding group varied throughout the period of sampling. Multivariate analyses indicates the ciliate communities were significantly different between the two habitats. Bottom water temperature and sediment grain size were the key factors that explained the ciliate community structure.

Regulating the migration of smooth muscle cells by a vertically distributed poly(2-hydroxyethyl methacrylate) gradient on polymer brushes covalently immobilized with RGD peptides.

The gradient localization of biological cues is of paramount importance to guide directional migration of cells. In this study, poly(2-hydroxyethyl methacrylate-co-glycidyl methacrylate)-block- poly(2-hydroxyethyl methacrylate) (P(HEMA-co-GMA)-b-PHEMA) brushes with a uniform underneath P(HEMA-co-GMA) layer and a gradient thickness of PHEMA blocks were prepared by using surface-initiated atom-transfer radical polymerization and a dynamically controlled polymerization process. The polymer chains were subsequently functionalized with the cell-adhesive arginine-glycine-aspartic acid (RGD) peptides by reaction with the glycidyl groups, and their structures and properties were characterized by X-ray photoelectron spectrometry (XPS), quartz crystal microbalance with dissipation (QCM-D) and air contact angle. Adhesion and migration processes of smooth muscle cells (SMCs) were then studied. Compared with those on the sufficiently exposed RGD surface, the cell adhesion and mobility were well maintained when the RGD peptides were localized at 18.9 nm depth, whereas the adhesion, spreading and migration rate of SMCs were significantly impaired when the RGD peptides were localized at a depth of 38.4 nm. On the RGD depth gradient surface, the SMCs exhibited preferential orientation and enhanced directional migration toward the direction of reduced thickness of the second PHEMA brushes. Half of the cells were oriented within ±â€¯30° to the x-axis direction, and 72% of the cells moved directionally at the optimal conditions. Cell adhesion strength, arrangement of cytoskeleton, and gene and protein expression levels of adhesion-related proteins were studied to corroborate the mechanisms, demonstrating that the cell mobility is regulated by the complex and synergetic intracellular signals resulted from the difference in surface properties. STATEMENT OF SIGNIFICANCE: Cell migration is of paramount importance for the processes of tissue repair and regeneration. So far, the gradient localization of biological cues perpendicular to the substrate, which is the usual case for the biological signaling molecules to locate in ECM in vivo, has been scarcely studied, and has not been used to guide the directional migration of cells. In this study, we prepare a depth gradient of RGD peptides along the polymer chains, which is used to guide the directional migration of SMCs after a second hydrophilic bock is prepared in a gradient manner. For the first time the directional migration of SMCs is achieved under the guidance of a depth gradient of RGD ligands. The mechanisms of different cell migration abilities are further discussed based on the results of cell adhesion, cell adhesion force, cytoskeleton alignment and expression of relative proteins and genes. This work paves a new strategy by fabricating a gradient polymer brushes with immobilized bioactive molecules to dominate the directional cell migration, and elucidates the mechanisms underlining the biased migration along RGD depth localization gradients, shedding a light for the design of novel biomaterials to control and guide cell migration and invasion.

Inter-annual changes in fish communities of a tropical bay in southeastern Brazil: What can be inferred from anthropogenic activities?

We assessed inter-annual changes in fish assemblages of a tropical bay which experienced a heavily industrialized process in the last decades. A highly significant difference in community structure among the bay zones, and a decrease in fish richness and abundance over time were found. Changes in fish richness and abundance between the two first (1987-1988 and 1993-1995) and the two latter time periods (1998-2001 and 2012-2013) were sharpest in the inner bay zone, the most impacted bay area, and in the middle zone, whereas the outer zone remained comparatively stable over time. These changes coincided with increased metal pollution (mainly, Zn and Cd) in the bay and with the enlargement of the Sepetiba Port. Spatial changes in the fish community structure among the bay zones were related to differences in salinity, transparency and depth with this latter variable acting as a buffer stabilizing temporal community changes.

DOC concentrations across a depth-dependent light gradient on a Caribbean coral reef.

Photosynthates released by benthic primary producers (BPP), such as reef algae and scleractinian corals, fuel the dissolved organic carbon (DOC) production on tropical coral reefs. DOC concentrations near BPP have repeatedly been observed to be elevated compared to those in the surrounding water column. As the DOC release of BPP increases with increasing light availability, elevated DOC concentrations near them will, in part, also depend on light availability. Consequently, DOC concentrations are likely to be higher on the shallow, well-lit reef terrace than in deeper sections on the fore reef slope. We measured in situ DOC concentrations and light intensity in close proximity to the reef alga Dictyota sp. and the scleractinian coral Orbicella faveolata along a depth-dependent light gradient from 5 to 20 m depth and compared these to background concentrations in the water column. At 10 m (intermediate light), DOC concentrations near Dictyota sp. were elevated by 15 µmol C L-1 compared to background concentrations in the water column, but not at 5 and 20 m (high and low light, respectively), or near O. faveolata at any of the tested depths. DOC concentrations did not differ between depths and thereby light environments for any of the tested water types. However, water type and depth appear to jointly affect in situ DOC concentrations across the tested depth-dependent light gradient. Corroborative ex situ measurements of excitation pressure on photosystem II suggest that photoinhibition in Dictyota sp. is likely to occur at light intensities that are commonly present on Curaçaoan coral reefs under high light levels at 5 m depth during midday. Photoinhibition may have thereby reduced the DOC release of Dictyota sp. and DOC concentrations in its close proximity. Our results indicate that the occurrence of elevated DOC concentrations did not follow a natural light gradient across depth. Instead, a combination of multiple factors, such as water type, light availability (including the restriction by photoinhibition), and water movement are proposed to interactively determine the DOC concentrations in the close vicinity of BPP.

Grazer identity changes the spatial distribution of cascading trophic effects in stream pools.

Non-lethal effects of predators on prey behavior can mediate trophic cascades, but the extent of effects depends on habitat characteristics and risk sensitivity of prey. Furthermore, predation risk for stream organisms varies along the depth gradient and strongly influences their behavior. Grazing minnows (Campostoma anomalum) and crayfish (Orconectes virilis) are both prey for largemouth bass (Micropterus salmoides) in streams, but differ in their predator-avoidance behavior. This study contrasts the effects and mechanisms of non-lethal trophic cascades on the spatial distribution of filamentous green algae among stream pools and along a depth gradient within pools. Presence/absence of a largemouth bass was crossed with four combinations of the two grazer species (0 grazers, 30 minnows, 30 crayfish, and 15 each) in outdoor, experimental streams. Grazer densities were maintained by restocking. I used geostatistics to quantify spatial patterns of predator and grazer habitat use, height of filamentous algae in the water column, and spatial covariation of water depth with algal height, and depth with grazer habitat use. In streams with only minnows, bass were sedentary, and hid within tall algae in a single "bass pool". In pools with grazed algae, bass actively pursued prey within and among pools and used deeper water. This set up a hierarchy of risk to grazers along the depth gradient from bass in deep water to potential risk from terrestrial predators in shallow water. Thus, minnows were more sensitive than crayfish to predation risk from bass, but less sensitive than crayfish to risk from terrestrial predators. Minnows mediated cascades at the scale of whole pools by avoiding "bass pools", but only if crayfish were absent. Crayfish avoided potential interactions both with terrestrial predators and bass by grazing and burrowing in deeper water at night (when bass were inactive), and by hiding in burrows during daytime. Crayfish without burrows avoided bass and crayfish defending burrows by using shallow edges of pools as corridors, but did not graze there. Thus, crayfish-mediated cascades were limited to pool edges. Effects of grazer identity may extend to other consumers via modification of risk for biota that use filamentous algae as either foraging or refuge habitat.