Differences In Vertical Distribution Research Articles

Risk Assessment of Trace Metals Using Chemical Speciation, Bioavailability, and Cluster Analysis Around Wadi EL Bey (Gulf of Tunis, Tunisia)

ABSTRACT The Wadi El Bey is one of the most vulnerable areas to pollution in the northeast of Tunisia, altered by anthropogenic and natural processes. This study uses the Community Bureau of Reference (BCR) approach and statistical tools, particularly the student’s t-test and the cluster analysis, to evaluate the danger of metals zinc (Zn), nickel (Ni), lead (Pb), cadmium (Cd), and copper (Cu) pose. This work is to assess the long-term evolution and mobility of heavy metals in the core soils of the Wadi El Bey River Bed. Heavy metals in SC1 followed the descending order Fe>Cu>Zn>Ni>Pb>Cd and in SC2 it was Fe>Cu>Zn>Ni>Cd>Pb. The (BCR) procedure showed that in soil cores SC1 and SC2, Ni was mainly associated with the exchangeable fractions (F1). However, the Zn and Cu were linked to the residual fractions (F4). The student’s t-test confirmed that the difference in vertical distribution between the SC1 and SC2 of Zn and Pb is statistically significant (p-value<.05) contrary to Ni (P = .06), Cd (P = .79), Cu (P = .38) demonstrated a common origin for these metals in the Wadi El Bey. The cluster analysis revealed that pH was the main responsible factor influencing the migration of Cu, Ni, and Zn toward the labile fractions in SC1. Whereas the total organic carbon influenced the Zn fixation in the most stable fraction in SC2. The use of pollution indices showed strong contamination by Ni, Cu, and Cd and moderate contamination by Zn and Pb. The risk assessment code (RAC) showed that Zn and Cu had a low to medium risk whereas medium to high risk for Ni. For better management and better control of heavy metal pollution in ecosystems with intermittent regimes, we advise a tertiary treatment of wastewater before evacuating it in Wadi el Bey.

Reduced pressure effects on smoke temperature, CO concentration and smoke extraction in tunnel fires with longitudinal ventilation and vertical shaft

Nowadays, high-altitude tunnels at reduced pressure are emerging in the world's road network. A better understanding of the temperature and CO concentration distribution as well as the shaft extraction performance during tunnel fires with combined longitudinal ventilation and shaft exhaust under reduced ambient pressure is particularly crucial for the tunnel fire protection design. Series of tunnel fire simulations were carried out with ambient pressures of 50 kPa–101 kPa, fire heat release rates (HRRs) of 3 MW and 10 MW, and longitudinal ventilation velocities of 0 m/s to 2 m/s. The results show that the reduced ambient pressure enhances the difference in vertical and longitudinal distribution of CO concentration and smoke temperature, while the longitudinal ventilation gradually weakens this difference in longitudinal distribution. The natural exhaust shaft reduces the difference in vertical distribution but increases the difference in longitudinal distribution. As the reduction of ambient pressure, the smoke extraction efficiency of the shaft will increase slowly. Longitudinal ventilation can enhance the shaft's smoke extraction performance, but the general smoke extraction efficiency of the shaft deteriorates with the increasing longitudinal ventilation velocity. This study provides a fundamental reference for tunnel natural ventilation system under different ambient pressures, particularly in high-altitude tunnel fires.

Length and colonization rates of roots associated with arbuscular or ectomycorrhizal fungi decline differentially with depth in two northern hardwood forests.

Ectomycorrhizal (EM) and arbuscular mycorrhizal (AM) fungi are often studied independently, and thus little is known regarding differences in vertical distribution of these two groups in forests where they co-occur. We sampled roots at two soil depths in two northern hardwood stands in Bartlett, New Hampshire, co-dominated by tree species that associate with AM or EM fungi. Root length of both groups declined with depth. More importantly, root length of EM plant species exceeded that of AM plants at 0-10-cm depth, while AM exceeded EM root length at 30-50-cm depth. Colonization rates were similar between mineral and organic portions of the shallow (0-10cm) samples for EM and AM fungi and declined dramatically with depth (30-50cm). The ratio of EM to AM fungal colonization declined with depth, but not as much as the decline in root length with depth, resulting in greater dominance by EM fungi near the surface and by AM fungi at depth. The depth distribution of EM and AM roots may have implications for soil carbon accumulation as well as for the success of the associated tree species.

Plankton monitoring in the Northwest Atlantic: a comparison of zooplankton abundance estimates from vertical net tows and Continuous Plankton Recorder sampling on the Scotian and Newfoundland shelves, 1999–2015

Abstract Assessment of zooplankton abundance, distribution, community composition, and temporal variability is critical to understanding the effects of climate variability and change on lower trophic level production and availability for consumption by larger consumers. Zooplankton sampling is performed across the Canadian continental shelf system by Fisheries and Oceans Canada's Atlantic Zone Monitoring Programme (AZMP). Sampling includes semi-monthly to monthly collection of zooplankton using vertical net tows (VNTs) deployed from near-bottom to surface at stations on the central Scotian Shelf (Stn 2, 150 m depth) and Newfoundland Shelf (Stn 27, 175 m depth), and by Continuous Plankton Recorders (CPRs) in the near-surface layers along routes over the Scotian and Newfoundland shelves (0–10 m depth). Here, we compare abundance metrics for 11 copepod taxa collected using both gear types in both regions between 1999 and 2015. Seasonal cycles of VNT and CPR abundance were similar for near-surface residents. VNT: CPR abundance ratios varied year-round for vertical migrants, as ontogenetic migrants shifted their vertical distribution, and as diel migrants changed their migratory behaviour. For some taxa, differences in annual average VNT: CPR abundance ratios between regions suggest differences in vertical distribution, while for others differences in inter-annual variability for VNT and CPR abundances suggest differences in the dynamics of the near- and sub-surface components of the populations.

Comparative analysis of Microcystis buoyancy in western Lake Erie and Saginaw Bay of Lake Huron

Microcystis is the predominant genus of harmful cyanobacterium in both Lake Erie and Saginaw Bay of Lake Huron and has the capacity to regulate the buoyancy of its colonies, sinking under certain conditions while floating towards the surface in others. Understanding the factors that control buoyancy is critical for interpretation of remote sensing data, modeling and forecasting harmful algal blooms within these two systems. To determine if Microcystis colony buoyancy in the two lakes responds similarly to diurnal light cycles, colony buoyant velocity (floating/sinking terminal velocity in a quiescent water column) and size were measured after manipulating the intensity of sunlight. Overall, there were more positively buoyant (floating) colonies in Lake Erie while most of the colonies in Saginaw Bay were negatively buoyant (sinking). In Lake Erie the colonies became less buoyant at increased light intensities and were less buoyant in the afternoon than in the morning. In both lakes, apparent colony density was more variable among small colonies (< 200 µm), whereas larger colonies showed a diminished response of density to light intensity and duration. These findings suggest that colony density becomes less plastic as colonies increase in size, leading to a weak relationship between size and velocity. These relationships may ultimately affect how the bloom is transported throughout each system and will help explain observed differences in vertical distribution and movement of Microcystis in the two lakes.

Separate Feeding Between the Pelagic Stage of the Squat Lobster Munida gregaria and the Larger Sized Zooplankton Crustacean Groups in the Beagle Channel as Revealed by Stable Isotopes

In southern Patagonia, the Beagle Channel shows very low production during winter but simultaneously sustains very dense aggregations of the pelagic stage of squat lobster (Munida gregaria), a benthic decapod whose pelagic juveniles have the largest body size within the chitinous pelagic community. To assess the coexistence of the mesozooplankton community and the pelagic M. gregaria stage under the harsh feeding winter conditions, we conducted a research cruise at two locations connected to the Beagle Channel, Yendegaia Bay (land terminating-glacier) and Pia Fjord (marine-terminating glacier). Our results showed that the zooplankton communities were similar in these two fjords, that a single pelagic group dominated in terms of biomass (pelagic Munida gregaria), and that differences in vertical distribution existed between most of the principal crustacean zooplankton and pelagic M. gregaria. All groups showed consumption of terrestrially derived organic matter, as revealed by their δ13C values. However, the isotopic composition, trophic positions (TP), and isotopic niche areas of the groups separated pelagic M. gregaria, presenting some of the lowest δ15N and the highest δ13C values, and the narrowest isotopic niche width. Pelagic M. gregaria was dominated by a single body size class along the 0–100 m water column, with no diel changes in vertical distribution, remained mostly in the upper layers (0–50 m), and benefited from the slightly higher phytoplankton concentrations at shallower depths as revealed by their higher δ13C values and low trophic position. In contrast, the other groups, including zoea M. gregaria stages, developed changes in distribution between day and night or remained deeper in the water column. These groups showed higher δ15N values, higher TP, and lower δ13C values, most of which probably fed on a nanoheterotrophs and terrestrial particulate organic matter mixture at deeper layers. Thus, the different vertical distributions, different trophic level food sources, and slightly different organic carbon sources apparently reduced any potential competence for food resources and form part of the feeding strategy that may facilitate the coexistence of the different large pelagic crustaceans under harsh feeding winter conditions in this high latitude austral region.

Niche differentiation of Dinophysis acuta and D. acuminata in a stratified fjord

Dinophysis acuta and D. acuminata are associated with lipophilic toxins in Southern Chile. Blooms of the two species coincided during summer 2019 in a highly stratified fjord system (Puyuhuapi, Chilean Patagonia). High vertical resolution measurements of physical parameters were carried out during 48 h sampling to i) explore physiological status (e.g., division rates, toxin content) and ii) illustrate the fine scale distribution of D. acuta and D. acuminata populations with a focus on water column structure and co-occurring plastid-bearing ciliates. The species-specific resources and regulators defining the realized niches (sensu Hutchinson) of the two species were identified. Differences in vertical distribution, daily vertical migration and in situ division rates (with record values, 0.76 d−1, in D. acuta), in response to the environmental conditions and potential prey availability, revealed their niche differences. The Outlying Mean Index (OMI) analysis showed that the realized niche of D. acuta (cell maximum 7 × 103 cells L−1 within the pycnocline) was characterized by sub-surface estuarine waters (salinity 23 – 25), lower values of turbulence and PAR, and a narrow niche breath. In contrast, the realized niche of D. acuminata (cell maximum 6.8 × 103 cells L−1 just above the pycnocline) was characterized by fresher (salinity 17 – 20) outflowing surface waters, with higher turbulence and light intensity and a wider niche breadth. Results from OMI and PERMANOVA analyses of co-occurring microplanktonic ciliates were compatible with the hypothesis of species such as those from genera Pseudotontonia and Strombidium constituting an alternative ciliate prey to Mesodinium. The D. acuta cell maximum was associated with DSP (OA and DTX-1) toxins and pectenotoxins; that of D. acuminata only with pectenotoxins. Results presented here contribute to a better understanding of the environmental drivers of species-specific blooms of Dinophysis and management of their distinct effects in Southern Chile.

Spatial distribution and morphometry of the succineid snail Succinea baconi (Pfeiffer, 1854) in India

The spatial distribution and morphological features of the land snail Succinea baconi (Pfeiffer, 1854) (Gastropoda: Succineidae) from India were evaluated. The survey performed in gardens and bushes in Coochbehar, West Bengal, India, has made it possible to assess the abundance of the snail S. baconi on the randomly selected lemon plants (n = 18). Logistic regressions were employed to judge differences in vertical distribution, resource association and size class variation in the snails under study. Variation in shell morphology was assessed by performing the regression analysis of the sampled shells of live snails (n = 258) and vacant shells of the deceased individuals (n = 100). An overall significant difference (p &lt; 0.05) in the vertical distribution of snails in lemon plants was observed. As to their association with resources available, snails were found to be more abundant in detritus than on living parts of the plants. The performed logistic regression revealed that the relative abundance of different S. baconi size classes was significantly different (p &lt; 0.001). Significant correlations (p &lt; 0.001) were found among different body size variables, with the shell length (x)-body weight (y) relationship being: y = 0.232x2.524 (for live snails) and the shell length (x)-shell weight (y) relationship being: y = 0.358x2.537 (for shells of dead snails). Various parameters of the snail shell shape could be represented through regression equations. Although reproduction and growth strategies of snails need to be explored further, the presented observations improve our understanding of the ecology of S. baconi, which may prove useful for future conservation efforts.

Assessment of plastic ingestion by pole-caught pelagic predatory fish from O'ahu, Hawai'i.

Although the frequency of occurrence of plastic ingestion in the large-sized dolphinfish and tunas taken by the Hawai'i longline fishery is very low (frequency of occurrence < 5% of sampled individuals), the ingestion of plastic in smaller-sized specimens caught with pole-and-line gear by commercial and recreational fishers has not been investigated.This study examined ingestion of >0.25 mm marine plastic debris (MPD) by four predatory fish species caught by commercial fishers around the Main Hawaiian Islands, and documented ingestion in three species: 85.7% of albacore tuna (n = 7), 40.0% of skipjack tuna (n = 10) and 12.5% of dolphinfish (n = 8).Yellowfin tuna (n = 10) did not contain any MPD, probably owing to the high proportion of empty stomachs (60%).For skipjack tuna, the frequency of occurrence of MPD ingestion was significantly higher for the smaller-sized specimens caught with pole-and-line (40%), compared with the larger-sized specimens caught with longlines (0%).For dolphinfish, the frequency of occurrence of MPD ingestion was similar for the similar-sized specimens caught with pole-and-line and with longlines.The ingested MPD items were micro-meso plastics, between 1 and 25 mm. While most ingested items were fragments, albacore also ingested line and skipjack also ingested sheets.The predatory fishes ingested light MPD items that float in sea water, but there were species-specific differences in their polymer composition: albacore contained more polypropylene and polyethylene, and skipjack contained more elastomers, characterized by a high percentage of ester plasticizers.Altogether, these results suggest that albacore and skipjack tunas ingest plastic of different types and polymers. Yet more research is needed to understand how differences in vertical distribution, foraging ecology and diet influence the MPD sampled by these predatory fish species.

The behavioral ecology and distribution of leptocephali: marine fish larvae with unforeseen abilities

Leptocephali are the unique larvae of eels and their relatives of the teleost superorder Elopomorpha that have remained poorly understood despite their ubiquitous presence at tropical to temperate latitudes. This review examines recent advancements in understanding the behavioral ecology and distribution of leptocephali. Their regional distributions and abundance are determined by when and where the adults spawn and seemingly if the larvae use active behavior for retention, passively drift, or swim actively to facilitate recruitment, but there is little direct evidence about their possible use of dispersal/retention or swimming behaviors. They typically reside within or above the thermocline at night offshore (< 100 m), some vertically migrate deeper during daytime (< 300 m), and they may move considerably deeper near continental shelves, but some also reside at the surface, and there may be taxonomic differences in vertical distributions. At what depths or times of day they feed on marine snow-associated materials is unclear. The extreme transparency of leptocephali and use of shape-change behaviors or expandable chromatophores along with their gut swellings or external appendages may be adaptations for reducing predation rates through Batesian mimicry of gelatinous zooplankton. Many questions remain about their behavior and ecology, but the basic strategy of the leptocephalus larval form appears to be based on feeding on readily available marine snow, behavioral abilities and morphological features to reduce predation, a body filled with transparent gelatinous energy reserves for active swimming, and growth to large sizes that enable recruitment at larger sizes than typical fish larvae.

Abundance, horizontal and vertical distribution of epipelagic ctenophores and scyphomedusae in the northern Bering Sea in summer 2017 and 2018: Quantification by underwater video imaging analysis

We examined the abundance and horizontal and vertical distributions of epipelagic ctenophores and scyphomedusae in the northern Bering Sea using an underwater video camera during July of 2017 and 2018. The effects of environmental and biological parameters on the distribution of these species were evaluated by generalized additive modelling (GAM). In 2017, the dominant ctenophore, Bolinopsis infundibulum, was mainly distributed in the north and west of St. Lawrence Island (SLI), and their vertical distribution varied with the region but not by the time of day. We found that B. infundibulum was distributed in the upper pycnocline north of SLI, but below the pycnocline west of SLI. Biological interactions with other gelatinous zooplankton may explain these regional differences in vertical distribution; GAM analysis revealed a negative interaction between B. infundibulum and the large scyphomedusa, Chrysaora melanaster, which occurred in the upper layer in the west of SLI. B. infundibulum may avoid that layer to reduce feeding competition. For the ctenophore, Beroe sp., vertical and horizontal distributions were similar to those of B. infundibulum, and GAM analysis also revealed a positive interaction for both species. As B. infundibulum is an important prey of Beroe sp., a prey-predator interaction may result from their similar horizontal and vertical distributions. Standing stocks of epipelagic ctenophores and scyphomedusae in 2018 were low compared to those in 2017, by a factor of 1/20 (C. melanaster) and1/90 (Beroe sp.). This might be due to annual differences in water mass in this region, in that the thermal conditions characterized by a high abundance of the dominant B. infundibulum in 2017 (<2 and >8 °C) were absent in 2018. As this drastic decrease in standing stock in 2018 was apparent for both ctenophores and scyphomedusae, food availability was hypothesized to be poor that year.

A comparative gene co-expression analysis using self-organizing maps on two congener filmy ferns identifies specific desiccation tolerance mechanisms associated to their microhabitat preference

BackgroundFilmy-ferns (Hymenophyllaceae) are poikilohydric, homoiochlorophyllous desiccation-tolerant (DT) epiphytes. They can colonize lower and upper canopy environments of humid forest. Filmy-ferns desiccate rapidly (hours), contrasting with DT angiosperms (days/weeks). It has been proposed that desiccation tolerance in filmy-ferns would be associated mainly with constitutive features rather than induced responses during dehydration. However, we hypothesize that the inter-specific differences in vertical distribution would be associated with different dynamics of gene expression within the dehydration or rehydration phases. A comparative transcriptomic analysis with an artificial neural network was done on Hymenophyllum caudiculatum (restricted to lower canopy) and Hymenophyllum dentatum (reach upper canopy) during a desiccation/rehydration cycle.ResultsRaw reads were assembled into 69,599 transcripts for H. dentatum and 34,726 transcripts for H. caudiculatum. Few transcripts showed significant changes in differential expression (DE). H. caudiculatum had ca. twice DE genes than H. dentatum and higher proportion of increased-and-decreased abundance of genes occurs during dehydration. In contrast, the abundance of genes in H. dentatum decreased significantly when transitioning from dehydration to rehydration. According to the artificial neural network results, H. caudiculatum enhanced osmotic responses and phenylpropanoid related pathways, whilst H. dentatum enhanced its defense system responses and protection against high light stress.ConclusionsOur findings provide a deeper understanding of the mechanisms underlying the desiccation tolerance responses of two filmy ferns and the relationship between the species-specific response and the microhabitats these ferns occupy in nature.

Micronekton biomass distribution, improved estimates across four north Atlantic basins

Distribution of micronekton was investigated during early summer of 2013, using data from a cruise covering the central parts of four north Atlantic basins, the Norwegian Sea (NS), Iceland Sea (ICS), Irminger Sea (IRS), and Labrador Sea (LS). Continuous underway acoustics mapped vertical and horizontal distributions, and trawl sampling provided data on biomass and taxonomic composition. The hull mounted acoustics and trawl catches suggested that, among the four basins, biomass of epipelagic, larger nektonic species (>20 cm length) during the cruise was highest in the NS and ICS basins, while mesopelagic non-gelatinous micronekton biomass peaked in the IRS and LS basins. Biomass of Scyphozoa was also about 1 order of magnitude higher in IRS and LS compared to ICS and NS. In ICS and NS, crustaceans made up about 50% of total non-gelatinous micronekton biomass, with fish making up less than 20% of total biomass. In contrast, fish constituted more than 60% of non-gelatinous biomass of catches in IRS and LS. In catches from ICS and NS the myctophid Benthosema glaciale dominated the catches, whereas bathylagids, gonostomatids, barracudinas and stomiids contributed to the high biomass densities of fish in IRS and LS. In addition to the differences in biomass between the basins, the acoustic measurements suggested gradients within the north-eastern basins, and large differences in vertical distribution of biomass between the basins during the cruise.

Can Lagrangian Tracking Simulate Tracer Spreading in a High-Resolution Ocean General Circulation Model?

AbstractTo model tracer spreading in the ocean, Lagrangian simulations in an offline framework are a practical and efficient alternative to solving the advective–diffusive tracer equations online. Differences in both approaches raise the question of whether both methods are comparable. Lagrangian simulations usually use model output averaged in time, and trajectories are not subject to parameterized subgrid diffusion, which is included in the advection–diffusion equations of ocean models. Previous studies focused on diffusivity estimates in idealized models but could show that both methods yield similar results as long as the deformations-scale dynamics are resolved and a sufficient amount of Lagrangian particles is used. This study compares spreading of an Eulerian tracer simulated online and a cloud of Lagrangian particles simulated offline with velocities from the same ocean model. We use a global, eddy-resolving ocean model featuring 1/20° horizontal resolution in the Agulhas region around South Africa. Tracer and particles were released at one time step in the Cape Basin and below the mixed layer and integrated for 3 years. Large-scale diagnostics, like mean pathways of floats and tracer, are almost identical and 1D horizontal distributions show no significant differences. Differences in vertical distributions, seen in a reduced vertical spreading and downward displacement of particles, are due to the combined effect of unresolved subdaily variability of the vertical velocities and the spatial variation of vertical diffusivity. This, in turn, has a small impact on the horizontal spreading behavior. The estimates of eddy diffusivity from particles and tracer yield comparable results of about 4000 m2 s−1 in the Cape Basin.

Vertical distribution of wandering spiders in Central America

We examined patterns of vertical distribution within an assemblage of seven species of large wandering spiders in a lowland rainforest on the Caribbean slope of Costa Rica. Over 16 months, 22 trees were surveyed regularly at night, up to a height of 43 m, using a rope climbing technique. Local climate and canopy microclimate exhibited only weak seasonal fluctuations. There was a distinct vertical segregation between ground-dwelling and arboreal species. The arboreal species used almost the entire available height range, whereby immature Cupiennius coccineus F.O.P.-Cambridge, 1901 occupied higher parts of the trees than adults. The two most abundant arboreal species differed also in their use of arboreal microhabitats: while Cu. coccineus occurred most frequently on trunk bark and on epiphyte leaves, the smaller Ctenus sp. 4 was more restricted to trunk bark. We detected effects of structural complexity of the host trees but no effects of canopy microclimate or of local climate on vertical distribution of Cu. coccineus, by far the most abundant arboreal species. The differences in vertical distribution both between age classes of Cu. coccineus, and between Cu. coccineus and the smaller Ctenus sp. 4 suggest size-dependent habitat segregation in arboreal species along the vertical axis, which might diminish cannibalism and/or intra-guild predation. Moreover, the wide range of vertical distribution of arboreal spiders suggests that they may connect the understory and canopy food webs.

Compatible solutes and metabolites accumulation does not explain partial desiccation tolerance in Hymenoglossum cruentum and Hymenophyllum dentatum (Hymenophyllaceae) two filmy ferns with contrasting vertical distribution

Hymenoglossum cruentum (Cav.) Presl. and Hymenophyllum dentatum (Cav.) are poikilohydric partial desiccation tolerant (PDT) epiphytic filmy ferns with contrasting vertical distributions. H. cruentum is restricted to trunk base (ground to 1 m), and H. dentatum is more generalist growing from the ground up to 9 m in the host. Vertical distribution has been related to interspecific differences to cope with greater desiccating conditions such as low humidity and high irradiance. PDT plants exhibit a series of mechanisms that allow them to better tolerate severe dehydration that include the accumulation of compatible solutes, and the de novo synthesis of proteins and free sugars that are thought to protect cellular structure during cycles of desiccation-rehydration. Therefore, interspecific differences in the capacity to accumulate compatible solutes and metabolites during desiccation-rehydration may explain differences in vertical distribution between these two “filmy fern” species. The contents of proline, glycine betaine, soluble sugars, total proteins, and pigments of the photosynthetic system were evaluated during a cycle of desiccation-rehydration in H. cruentum and H. dentatum. The latter exhibited a more rapid desiccation-rehydration cycle in contrast to the former. Soluble sugars, proline, and pigment contents decreased in the dehydrated state. The two filmy ferns did not exhibit a major accumulation of proline (lower than 8 μmol g−1 DW) or glycine betaine (lower than 4 mg g−1 DW) which contrasts with other higher plants exposed to water deficit. Both species exhibited an elevated sugar concentration in the hydrated state, which decreased during desiccation by approximately 2.5-fold. These results differ from previous studies on other desiccation tolerant higher-plants but agree with results from bryophytes. We concluded that accumulation of conventional compatible solutes of higher plants is not part of the dehydration induced mechanisms conferring desiccation tolerance in filmy ferns, and do not explain interspecific differences in vertical distribution of the two species. Therefore, partial desiccation tolerance of filmy ferns probably relies on preformed structural rather than induced biochemical mechanisms, suggesting similarities of Hymenophyllaceae (primitive ferns) with bryophytes.

Vertical distribution of larval Atlantic menhaden (Brevoortia tyrannus) and Atlantic croaker (Micropogonias undulatus): Implications for vertical migratory behaviour and transport

AbstractUnderstanding the interactions among biological and physical processes is essential to determining how the environment affects transport and survival of fishes. We examined vertical distribution in larval Atlantic menhaden (Brevoortia tyrannus) and Atlantic croaker (Micropogonias undulatus) using 126 depth stratified tows in Delaware Bay, USA, during two cruises, in December 2007 and February 2008. Menhaden larvae were 16.8–24.6 and 20.5–26.2 mm standard length in December and February. Corresponding lengths for croaker were 9.3–17.9 and 8.6–19.6 mm. Using empirical observations, and statistically derived models, we explored larval concentration for both species as a function of location, depth, diel period, tidal period, size, and pairwise interactions. Menhaden concentration was best modeled as a function of station, cruise, and interactions between depth and size as well as between station and cruise. No significant differences in larval menhaden concentration were present among tidal and diel periods. Croaker concentration was best modeled as a function of size and interactions between station and diel period, depth and size, cruise and size. Despite tidal period not emerging as a significant model parameter, we observed larger croaker larvae during nighttime flood tides. Our statistical models are consistent with processes of up‐estuary transport for both species, suggesting larvae are increasingly affected by behavioral responses as larvae grow, exhibiting stronger patterns in vertical distribution. The results refine our understanding of the potential importance of size‐related differences in vertical distribution for larval transport in these species. Future research should examine the interactions among size‐specific vertical migratory capabilities, vertical distribution, transport, and retention.

Origin and diversification of Lake Ohrid's endemic acroloxid limpets: the role of geography and ecology.

BackgroundAncient Lake Ohrid, located on the Albania-Macedonia border, is the most biodiverse freshwater lake in Europe. However, the processes that gave rise to its extraordinary endemic biodiversity, particularly in the species-rich gastropods, are still poorly understood. A suitable model taxon to study speciation processes in Lake Ohrid is the pulmonate snail genus Acroloxus, which comprises two morphologically distinct and ecologically (vertically) separated endemic species. Using a multilocus phylogenetic framework of Acroloxus limpets from the Euro-Mediterranean subregion, together with molecular-clock and phylogeographic analyses of Ohrid taxa, we aimed to infer their geographic origin and the timing of colonization as well as the role of geography and ecology in intra-lacustrine diversification.ResultsIn contrast to most other endemic invertebrate groups in Lake Ohrid, the phylogenetic relationships of the endemic Ohrid Acroloxus species indicate that the Balkan region probably did not serve as their ancestral area. The inferred monophyly and estimated divergence times further suggest that these freshwater limpets colonized the lake only once and that the onset of intra-lacustrine diversification coincides with the time when the lake reached deep-water conditions ca 1.3 Mya. However, the difference in vertical distribution of these two ecologically distinct species is not reflected in the phylogeographic pattern observed. Instead, western and eastern populations are genetically more distinct, suggesting a horizontal structure.ConclusionsWe conclude that both geography and ecology have played a role in the intra-lacustrine speciation process. Given the distinct morphology (sculptured vs. smooth shell) and ecology (littoral vs. sublittoral), and the timing of intra-lacustrine diversification inferred, we propose that the onset of deep-water conditions initially triggered ecological speciation. Subsequent geographic processes then gave rise to the phylogeographic patterns observed today. However, the generally weak genetic differentiation observed suggests incipient speciation, which might be explained by the comparatively young age of the lake system and thus the relatively recent onset of intra-lacustrine diversification.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0826-6) contains supplementary material, which is available to authorized users.

Diel vertical migration and cross-shore distribution of barnacle and bivalve larvae in the central Chile inner-shelf

The vertical and horizontal distribution of larval stages of the most common intertidal barnacle and mussel species were characterized in near-shore waters of central Chile. Paired day/night cruises were conducted on four spring-summer dates between December 2007 and November 2008, under contrasting wind, wave height, and near-shore stratification conditions. Regardless of variability in oceanographic conditions, the highest abundances of barnacle and mussel larvae were found within 1500m from shore. Non-uniform vertical distributions were observed for chthamalids, balanids and mussel larvae, but patterns of diel variability differed among them. Chthamalid and balanid nauplii, as well as balanid cyprids were more abundant in the upper 20m of the water column, while the density of chthamalid cyprids was highest near the bottom. Mussel larvae were only found within 20m of the surface. The Mean Depth Distribution (MDD) of all nauplii (balanid and chthamalid) and chthamalid cyprids was deeper during day than night, suggesting typical diel vertical migration (DVM), but this difference was statistically significant only for nauplii. Mussels did not show diel differences in vertical distribution. The amplitude of DVM, measured as the difference between daytime and nighttime MDD, decreased with increasing wave height in chthamalid and balanid nauplii, but not with along-shore wind stress. Chthamalid nauplii, and to a lesser extent, balanid nauplii were found below the pycnocline during the day and above at night, suggesting that DVM involves daily crossing of this density barrier. In contrast, cyprids of all barnacle species were distributed across the pycnocline with no clear pattern. The results suggest that barnacle and bivalve larvae may exhibit a variety of behavioral responses to position themselves in the water column despite typically turbulent near-shore waters, and that such behavior varies between species and through ontogeny within species. Moreover, some stages of barnacle larvae perform DVM, but the amplitude decreased with increasing wave height – which may be either a plastic response to environmental cues or merely turbulent mixing impeding the ability of larvae to perform vertical migration.

Contrasting dynamic characteristics of shear turbulence and Langmuir circulation in the surface mixed layer

Large eddy simulation (LES) is used to investigate contrasting dynamic characteristics of shear turbulence (ST) and Langmuir circulation (LC) in the surface mixed layer (SML). ST is usually induced by wind forcing in SML. LC can be driven by wave-current interaction that includes the roles of wind, wave and vortex forcing. The LES results show that LC suppresses the horizontal velocity and greatly modifies the downwind velocity profile, but increases the vertical velocity. The strong downwelling jets of LC accelerate and increase the downward transport of energy as compared to ST. The vertical eddy viscosity K m of L is much larger than that of ST. Strong mixing induced by LC has two locations. They are located in the 2δ s–3δ s (Stokes depth scale) and the lower layer of the SML, respectively. Its value and position change periodically with time. In contrast, maximum K m induced by ST is located in the middle depth of the SML. The turbulent kinetic energy (TKE) generated by LC is larger than that by ST. The differences in vertical distributions of TKE and K m are evident. Therefore, the parameterization of LC cannot be solely based on TKE. For deep SML, the convection of large-scale eddies in LC plays a main role in downward transport of energy and LC can induce stronger velocity shear (S 2) near the SML base. In addition, the large-scale eddies and S 2 induced by LC is changing all the time, which needs to be fully considered in the parameterization of LC.