Uranium and other trace elements’ distribution in Korean granite: implications for the influence of iron oxides on uranium migration

To understand trace radionuclide (uranium) migration occurring in rocks, a granitic batholith located at the Korea Atomic Energy Research Institute (KAERI) site was selected and investigated. The rock samples obtained from this site were examined using mineralogical methods, including scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). The changes in the distribution pattern of uranium (U) and small amounts of trace elements, and the mineralogical textures affected by weathering, were examined. Based on the element distribution analyses, it was found that Fe²⁺ released from fresh biotite is oxidized in short geological time, forming amorphous iron oxides, such as ferrihydrite, around silicate minerals. In that case, the amorphous ferrihydrite does not show distinct adsorption for U. However, as it gradually crystallizes to goethite or hematite, the most U-rich phases were found to be associated with the secondary iron oxides having granular forms. This evidence suggests that the geological subsurface environment is favorable for the crystallized iron oxides to keep their structures more stable for a long time as compared with the amorphous phases. There is a possibility that the long residence of U which is in contact with the stable crystalline phases of iron may finally lead to the partial sequestration of U in their structure. Consequently, it seems that Fe-oxide crystallization can be a dominating mechanism for U uptake and controls long-term U transport in granites with low U contents.     

Network structure and parasite transmission in a group living lizard,the gidgee skink, <Emphasis Type="Italic">Egernia stokesii</Emphasis>

Gidgee skinks (Egernia stokesii) form large social aggregations in rocky outcrops across the Flinders Ranges in South Australia. Group members share refuges (rock crevices), which may promote parasite transmission. We measured connectivity of individuals in networks constructed from patterns of common crevice use and observed patterns of parasitism by three blood parasites (Hemolivia, Schellackia and Plasmodium) and an ectoparasitic tick (Amblyomma vikirri). Data came from a 1-year mark-recapture study of four populations. Transmission networks were constructed to represent possible transmission pathways among lizards. Two lizards that used the same refuge within an estimated transmission period were considered connected in the transmission network. An edge was placed between them, directed towards the individual that occupied the crevice last. Social networks, a sub-set of same-day only associations, were small and highly fragmented compared with transmission networks, suggesting that non-synchronous crevice use leads to more transmission opportunities than direct social association. In transmission networks, lizards infested by ticks were connected to more other tick-infested lizards than uninfected lizards. Lizards infected by ticks and carrying multiple blood parasite infections were in more connected positions in the network than lizards without ticks or with one or no blood parasites. Our findings suggest higher levels of network connectivity may increase the risk of becoming infected or that parasites influence lizard behaviour and consequently their position in the network. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. This contribution is part of the special issue “Social Networks: new perspectives” (Guest Editors: J. Krause, D. Lusseau and R. James).     

Predicted impact of ocean acidification on a marine invertebrate: elevated CO<Subscript>2</Subscript> alters response to thermal stress in sea urchin larvae

Ocean acidification (OA) and the biological consequences of altered seawater chemistry have emerged as a significant environmental threat to healthy marine ecosystems. Because a more acidic ocean interferes with fixation of calcium carbonate to form shells or calcified skeletons, future ocean chemistry may significantly alter the physiology of calcifying marine organisms. These alterations may manifest themselves directly in the calcification process, or have synergistic effects with other environmental factors such as elevated temperatures. New tools permit us to explore subtle changes in gene expression patterns in response to environmental conditions. We raised sea urchins (Strongylocentrotus franciscanus) under conditions simulating future atmospheric CO₂ levels of 540 and 970 ppm. When larvae raised under elevated CO₂ conditions were subjected to 1-h acute temperature stress, their ability to mount a physiological response (as measured by expression of the molecular chaperone hsp70) was reduced relative to those raised under ambient CO₂ conditions. These results represent the first use of gene expression assays to study the effects of OA on sea urchin development. They highlight the importance of looking at multiple environmental factors simultaneously as this approach may reveal previously unsuspected biological impacts of atmospheric changes.     

Quantification of copepod gut content by differential length amplification quantitative PCR (dla-qPCR)

Quantification of feeding rates and selectivity of zooplankton is vital for understanding the mechanisms structuring marine ecosystems. However, methodological limitations have made many of these studies difficult. Recently, molecular based methods have demonstrated that DNA from prey species can be used to identify zooplankton gut contents, and further, quantitative gut content estimates by quantitative PCR (qPCR) assays targeted to the 18S rRNA gene have been used to estimate feeding rates in appendicularians and copepods. However, while standard single primer based qPCR assays were quantitative for the filter feeding appendicularian Oikopleura dioica, feeding rates were consistently underestimated in the copepod Calanus finmarchicus. In this study, we test the hypothesis that prey DNA is rapidly digested after ingestion by copepods and describe a qPCR-based assay, differential length amplification qPCR (dla-qPCR), to account for DNA digestion. The assay utilizes multiple primer sets that amplify different sized fragments of the prey 18S rRNA gene and, based on the differential amplification of these fragments, the degree of digestion is estimated and corrected for. Application of this approach to C. finmarchicus fed Rhodomonas marina significantly improved quantitative feeding estimates compared to standard qPCR. The development of dla-qPCR represents a significant advancement towards a quantitative method for assessing in situ copepod feeding rates without involving cultivation-based manipulation.     

Delayed ontogenic dietary shift and high levels of omnivory in green turtles (<Emphasis Type="Italic">Chelonia mydas</Emphasis>) from the NW coast of Africa

Young green turtles (Chelonia mydas) spend their early lives as oceanic omnivores with a prevalence of animal prey. Once they settle into neritic habitats (recruitment), they are thought to shift rapidly to an herbivorous diet, as revealed by studies in the Greater Caribbean. However, the precise timing of the ontogenic dietary shift and the actual relevance of animal prey in the diet of neritic green turtles are poorly known elsewhere. Stable isotopes of carbon, sulfur and nitrogen in the carapace scutes of 19 green turtles from Mauritania (NW Africa), ranging from 26 to 102 cm in curved carapace length (CCLmin), were analyzed to test the hypothesis of a rapid dietary shift after recruitment. Although the length of residence time in neritic habitats increased with turtle length, as revealed by a significant correlation between turtle length and the δ¹³C and the δ³⁴S of the scutes, comparison of the δ¹⁵N of the innermost and outermost layers of carapace scutes demonstrated that consumption of macrophytes did not always start immediately after recruitment, and turtles often resumed an animal-based diet after starting to graze on seagrasses. As a consequence, seagrass consumption did not increase gradually with turtle size and animal prey largely contributed to the diet of turtles within the range 29–59 cm CCLmin (76–99% of assimilated nutrients). Seagrass consumption by turtles larger than 59 cm CCLmin was higher, but they still relied largely on animal prey (53–76% of assimilated nutrients). Thus, throughout most of their neritic juvenile life, green turtles from NW Africa would be better classified as omnivores rather than herbivores. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Arsenite oxidation by <Emphasis Type="Italic">Alcaligenes</Emphasis> sp. strain RS-19 isolated from arsenic-contaminated mines in the Republic of Korea

Arsenite [As(III)]-oxidizing bacteria play important roles in reducing arsenic [As] toxicity and mobility in As-contaminated areas. As-resistant bacteria were isolated from the soils of two abandoned mines in the Republic of Korea. The isolated bacteria showed relatively high resistances to As(III) up to 26 mM. The PCR-based 16S rRNA analysis revealed that the isolated As-resistant bacteria were close relatives to Serratia marcescensa, Pseudomonas putida, Pantoea agglomerans, and Alcaligenes sp. Among the five As-resistant bacterial isolates, Alcaligenes sp. strain RS-19 showed the highest As(III)-oxidizing activity in batch tests, completely oxidizing 1 mM of As(III) to As(V) within 40 h during heterotrophic growth. This study suggests that the indigenous bacteria have evolved to retain the ability to resist toxic As in the As-contaminated environments and moreover to convert the species to a less toxic form [e.g., from As(III) to As(V)] and also contribute the biogeochemical cycling of As by being involved in speciation of As.     

The effects of temperature and salinity on reproductive success of <Emphasis Type="Italic">Temora longicornis</Emphasis> in the Baltic Sea: a copepod coping with a tough situation

At specific locations within the Baltic Sea, thermoclines and haloclines can create rapid spatial and temporal changes in temperature (T) and salinity (S) exceeding 10°C and 9 psu with seasonal ranges in temperature exceeding 20°C. These wide ranges in abiotic factors affect the distribution and abundance of Baltic Sea copepods via species-specific, physiological-based impacts on vital rates. In this laboratory study, we characterized the influence of T and S on aspects of reproductive success and naupliar survival of a southwestern Baltic population of Temora longicornis (Copepoda: Calanoida). First, using ad libitum feeding conditions, we measured egg production (EP, no. of eggs female⁻¹ day⁻¹) at 12 different temperatures between 2.5 and 24°C, observing the highest mean EP at 16.9°C (12 eggs female⁻¹ day⁻¹). Next, the effect of S on EP and hatching success (HS, %) was quantified at 12°C for cohorts that had been acclimated to either 8, 14, 20 or 26 psu and tested at each of five salinities (8, 14, 20, 26 and 32 psu). The mean EP was highest for (and maximum EP similar among) 14, 20 and 26 psu cohorts when tested at their acclimation salinity whereas EP was lower at other salinities. For adults reared at 8 psu, a commonly encountered salinity in Baltic surface waters, EP was relatively low at all test salinities—a pattern indicative of osmotic stress. When incubated at 12°C and 15 different salinities between 0 and 34 psu, HS increased asymptotically with increasing S and was maximal (82.6–84.3%) between 24 and 26 psu. However, HS did depend upon the adult acclimation salinity. Finally, the 48-h survival of nauplii hatched and reared at 14 psu at one of six different temperatures (10, 12, 14, 16, 18 and 20°C) was measured after exposure to a novel salinity (either 7 or 20 psu). Upon exposure to 7 psu, 48-h naupliar mortality increased with increasing temperature, ranging from 26.7% at 10°C to 63.2% at 20°C. In contrast, after exposure to 20 psu, mortality was relatively low at all temperatures (1.7% at 10°C and ≤26.7% for all other temperatures). An intra-specific comparison of EP for three different T. longicornis populations revealed markedly different temperature optima and clearly demonstrated the negative impact of brackish (Baltic) salinities. Our results provide estimates of reproductive success and early survival of T. longicornis to the wide ranges of temperatures and salinities that will aid ongoing biophysical modeling examining climate impacts on this species within the Baltic Sea.     

Phylogenetic relationships of coral-associated gobies (Teleostei,Gobiidae) from the Red Sea based on mitochondrial DNA data

Bryaninops, Gobiodon, Paragobiodon and Pleurosicya are the most abundant genera of coral-associated gobies. These genera are adapted to live among coral, while other small reef gobies (e.g., the genus Eviota) show no obligate association with this living substrate. Thirteen coral-associated species and two Eviota species were sampled from different regions of the Red Sea, along with four populations/species of Gobiodon from the Indian and western Pacific Oceans. A molecular phylogenetic analysis was performed using partial sequences of 12S rRNA, 16S rRNA and cytochrome b mitochondrial genes, 1,199 base pairs in total. Several clades were consistently resolved in neighbor joining-, maximum parsimony-, maximum likelihood and Bayesian analyses. While each of the four genera Gobiodon, Paragobiodon, Bryaninops and Pleurosicya proved to be monophyletic, their relative position in the phylogeny did not support an emergence of coral-associated gobiids as a monophyletic assemblage. Instead, two separate monophyletic sub-groups were discovered, the first comprising Gobiodon and Paragobiodon, and the second Bryaninops and Pleurosicya. Our molecular phylogenetic examinations also revealed one unassigned species of Gobiodon from the Maldives as a distinct species and confirmed three putative and yet unassigned species from the Red Sea. Moreover, the uniformly black colored species of Gobiodon are not monophyletic but have evolved independently within two distinct species groups. Genetic distances were large in particular within Pleurosicya and Eviota. Estimated divergence times suggest that coral-associated gobies have diversified in parallel to their preferred host corals. In particular, divergence times of Gobiodon species closely match those estimated for their typical host coral genus Acropora.     

Sulfide assimilation by ectosymbionts of the sessile ciliate, <Emphasis Type="Italic">Zoothamnium niveum</Emphasis>

We investigated the constraints on sulfide uptake by bacterial ectosymbionts on the marine peritrich ciliate Zoothamnium niveum by a combination of experimental and numerical methods. Protists with symbionts were collected on large blocks of mangrove-peat. The blocks were placed in a flow cell with flow adjusted to in situ velocity. The water motion around the colonies was then characterized by particle tracking velocimetry. This shows that the feather-shaped colony of Z. niveum generates a unidirectional flow of seawater through the colony with no recirculation. The source of the feeding current was the free-flowing water although the size of the colonies suggests that they live partly submerged in the diffusive boundary layer. We showed that the filtered volume allows Z. niveum to assimilate sufficient sulfide to sustain the symbiosis at a few micromoles per liter in ambient concentration. Numerical modeling shows that sulfide oxidizing bacteria on the surfaces of Z. niveum can sustain 100-times higher sulfide uptake than bacteria on flat surfaces, such as microbial mats. The study demonstrates that the filter feeding zooids of Z. niveum are preadapted to be prime habitats for sulfide oxidizing bacteria due to Z. niveum’s habitat preference and due to the feeding current. Z. niveum is capable of exploiting low concentrations of sulfide in near norm-oxic seawater. This links its otherwise dissimilar habitats and makes it functionally similar to invertebrates with thiotrophic symbionts in filtering organs. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Going deep: common murres dive into frigid water for aggregated,persistent and slow-moving capelin

Owing to the necessity of delivering food to offspring at colonies, breeding seabirds are highly constrained in their foraging options. To minimize constraints imposed by central-place foraging and to optimize foraging behavior, many species exhibit flexible foraging tactics. Here we document the behavioral flexibility of pursuit-diving common murres Uria aalge when foraging on female capelin Mallotus villosus in the northwest Atlantic. Quite unexpectedly, being visual foragers, we found that common murres dived throughout the day and night. Twenty-one percent of recorded dives (n = 272 of 1,308 dives) were deep (≥50 m; maximum depth = 152 m, maximum duration = 212 s), bringing murres into sub-0°C water in the Cold Intermediate Layer (CIL; 40–180 m) of the Labrador Current. Deep dives occurred almost exclusively during the day when murres would have encountered spatially predictable aggregations of capelin between 100 and 150 m in the water column. Temperatures within the CIL shaped trophic interactions and involved trade-offs for both predators and prey. Sub-0°C temperatures limit a fish’s ability to escape from endothermic predators by reducing burst/escape speeds and also lengthening the time needed to recover from burst-type activity. Thus, while deep diving may be energetically costly, it likely increases certainty of prey capture. Decreased murre foraging efficiency at night (indicated by an increase in the number of dives per bout) reflects both lower light conditions and changing prey behavior, as capelin migrate to warmer surface waters at night where their potential to escape from avian predators could increase.