Increase in Alphaproteobacteria in association with a polychaete,Capitella sp. I,in the organically enriched sediment

We conducted bioremediation experiments on the organically enriched sediment on the sea floor just below a fish farm, introducing artificially mass-cultured colonies of deposit-feeding polychaete, Capitella sp. I. To clarify the association between the Capitella and bacteria on the efficient decomposition of the organic matter in the sediment in the experiments, we tried to identify the bacteria that increased in the microbial community in the sediment with dense patches of the Capitella. The relationship between TOC and quinone content of the sediment as an indicator of the bacterial abundance was not clear, while a significant positive correlation was found between Capitella biomass and quinone content of the sediment. In particular, ubiquinone-10, which is present in members of the class Alphaproteobacteria, increased in the sediment with dense patches of the Capitella. We performed denaturing gradient gel electrophoresis (DGGE) analyses to identify the alphaproteobacterial species in the sediment with dense patches of the worm, using two DGGE fragments obtained from the sediment samples and one fragment from the worm body. The sequences of these DGGE fragments were closely related to the specific members of the Roseobacter clade. In the associated system with the Capitella and the bacteria in the organically enriched sediment, the decomposition of the organic matter may proceed rapidly. It is very likely that the Capitella works as a promoter of bacteria in the organically enriched sediment, and feeds the increased bacteria as one of the main foods, while the bacteria decompose the organic matter in the sediment with the assistance of the Capitella.     

Larval development and metamorphic behaviour of the subtropical spionid polychaete Pseudopolydora vexillosa

Although newly described, Pseudopolydora vexillosa is one of the most conspicuous surface-feeding spioniform polychaetes in subtropical waters. This is the first report on larval growth and metamorphosis of P. vexillosa. Newly hatched (3-chaetigers stage) larvae of P. vexillosa reached metamorphic competence at 12-17 chaetigers stage when fed with Chaetoceros gracilis or Dunaliella tertiolecta at a concentration of ∼ 10⁵ cells ml^− 1 for 6 to 8 days at 32 psu and 27 °C. Larvae on these two diets achieved comparable levels, of approximately 70% metamorphosis. On the other hand, larvae fed with Isochrysis galbana or starved in 0.22 μm filtered seawater never reached competence during the 10 days of study. The effect of organic matter on larval substrate selection was examined using glass beads, manipulated sediments and natural sediments. A significantly higher percentage of larvae metamorphosed on glass beads that had been submerged in unfiltered natural seawater for 5 days as compared to the control; when manipulating the organic content of sediment as a substratum, significantly more larvae metamorphosed in 100% natural sediment, compared with 0%, 25%, 50%, and 75% natural sediment mixed with different portions of ashed sediment. Surprisingly, with natural undisturbed surface sediment sampled along a transect perpendicular to a sewage discharge site, these laboratory bioassays demonstrate that the larvae of P. vexillosa are capable of responding to sedimentary cues in complex ways to find a habitat suitable for metamorphosis and survival.     

Growth,biomass allocation,and autofragmentation responses to root and shoot competition in Myriophyllum spicatum as a function of sediment nutrient supply

Plant growth, biomass allocation and autofragmentation were investigated in response to root and shoot competition in the submersed macrophyte Myriophyllum spicatum L. growing in two sediment environments. Biomass accumulation and allocation were significantly affected by sediment fertility, with a higher total biomass observed in fertile sediment (average: 4.69 g per plant vs. 1.12 g per plant in infertile sediment). Root-to-shoot ratios were 0.34 and 0.06 in the infertile and fertile sediments, respectively, reflecting the high investment placed on roots under infertile conditions. In the presence of root, shoot, and full competition, whole plant biomass decreased by 18%, 12% and 24% in the infertile sediments, and 23%, 25% and 33% in the fertile sediments, respectively. Root weight ratios (RWRs) increased with root competition by 38% (P < 0.001) and 12% (P = 0.002), while leaf weight ratios (LWRs) decreased with shoot competition by 6% (P = 0.042) and 5% (P = 0.001) in the infertile and fertile sediments, respectively. A total of 406 autofragments were harvested in the fertile sediments, but none were obtained from the infertile sediments. In the control, autofragment number and biomass was 166% and 175% higher compared to the competition treatment. Root and shoot competition resulted in a 21% (P = 0.043) and 18% (P = 0.098) decrease in the autofragment biomass, respectively. These results indicated that M. spicatum responds to different sediment fertility by changing its allocation patterns. Moreover, both root and shoot competition influenced plant growth and autofragmentation, while sediment nutrient availability played an important role in M. spicatum autofragmentation.     

Recruitment of the infaunal bivalve Soletellina alba (Lamarck, 1818) (Bivalvia: Psammobiidae) in response to different sediment types and water depths within the intermittently open Hopkins River estuary

Studies examining recruitment processes for soft-sediment macroinvertebrate fauna in intermittent estuaries are rare and most studies of active habitat selection have been tested in the laboratory rather than the field. The present field study examined whether recruitment of the infaunal bivalve Soletellina alba was influenced by water depth and sediment particle size in the intermittent Hopkins River estuary, southern Australia. The number of recruits in sediment trays differed between water depths, but active habitat selection was not evident across treatments of varying sediment particle size. The use of sediments with varying particle sizes also provided an opportunity to identify potential discontinuities in body-size distributions of recruits associated with varying habitat architecture. The length (mm) of recruits was converted to the same scale used to express sediment particle size (i.e. phi units: ? = − log₂ of sediment particle size). The size of recruits differed across water depths, but did not differ across treatments with fine (? = 3) versus coarse (? = 1) sediment, and no relationships were apparent between bivalve size and sediments consisting of varying particle size. These patterns of recruitment do not correspond with the distribution of adult S. alba within the Hopkins River estuary. Previous sampling has shown that abundances of juvenile and adult S. alba are variable across time, site and water depth, but are often greater at the deeper water depth (1.05 m below the Australian Height Datum). However, recruitment during the present study was greatest at the shallower water depth (0.05 m below AHD), and the apparent absence of active habitat selection suggests that the distribution of adults is unlikely to be attributable to differences in recruitment associated with sediments of varying particle size.     

A preliminary assessment of rain throughfall beneath Portulacaria afra canopy in subtropical thicket and its implications for soil carbon stocks

Subtropical thicket dominated by the leaf- and stem-succulent tree Potulacaria afra (spekboom) accumulates extraordinarily high amounts of soil organic carbon for a semi-arid ecosystem. This has been attributed to high leaf litter production of canopy trees — especially spekboom — and the relatively cool beneath-canopy temperatures, which reduces mineralization of organic matter. High rainfall interception by the dense thicket canopy may also contribute to reduced mineralization of soil organic carbon stocks via a reduced Birch effect (wet-dry cycles) and overall reduced moisture of organic matter. Here we provide preliminary data on one easily measurable component of canopy interception, namely throughfall, which is the amount of rain falling on the canopy that is not intercepted by the canopy or diverted as stemflow. For 23 rainfall events > 1 mm in the period Jan-Jun 2006, we measured 275 ± 21 mm gross rainfall at three spekboom thicket sites. Mean throughfall was 56.4% across all events and ≤ 20% for small (≤ 5 mm) events. These values are the lowest recorded in the literature. Throughfall in tropical and temperate forests ranges from 70 to 90%, Mediterranean woodland trees 70-80%, and Savanna trees 75-84%. The low rates of throughfall recorded in this study support the hypothesis that the extreme accumulation of soil organic carbon in thicket soils is partly due to interception of rainfall and concomitant constraints on soil microbial activity. The extraordinary high interception of rainfall by the spekboom thicket canopy warrants further research at the ecosystem level.     

Interactive effects of porewater nutrient enrichment, bioturbation and sediment characteristics on benthic assemblages in sandy sediments

Effective management of eutrophic ecosystems requires an understanding of how nutrient input affects the structure and function of benthic communities. The effects of nutrients in soft sediment habitats can be influenced by a variety of factors including sediment characteristics, hydrodynamic exposure, and the presence of bioturbating macroinvertebrates. We used a large scale exclusion experiment (400 m² areas, n = 6) to test if bioturbating lugworms, Arenicola marina mediate the effects of nutrient enrichment. We incorporated small plots (30 × 30 cm) dosed with household garden fertilizer within the lugworm exclusion and corresponding control areas and predicted that the effects of nutrient enrichment would be greater in the absence of lugworms. We found that the increases in nutrient concentrations were higher in the absence of lugworms, but only in the less permeable sediment in the low intertidal zone compared to the more permeable sediment in the high intertidal. Contrary to expectations, the accumulation of nutrients in the plots did not affect the organic matter and chlorophyll levels in the sediment. Interestingly, there were overall negative effects of nutrient additions on some of the most abundant molluscs, Hydrobia ulvae, Retusa obtusa and juvenile Cerastoderma edule. Possible explanations for these adverse effects such as the changes in the sediment chemistry or the physical presence of the fertilizer in the sediment caused by the nutrient additions are discussed. We conclude that the effects of nutrient enrichment in soft sediment habitats on benthic assemblages are determined by the interplay between the presence of bioturbating macroinvertebrates, tidal height and sediment characteristics.     

An insight into the feeding ecology of deep-sea canyon nematodes — Results from field observations and the first in-situC feeding experiment in the Nazaré Canyon

Submarine canyon systems provide a heterogeneous habitat for deep-sea benthos in terms of topography, hydrography, and the quality and quantity of organic matter present. Enhanced meiofauna densities as found in organically enriched canyon sediments suggest that nematodes, as the dominant metazoan meiobenthic taxon, may play an important role in the benthic food web of these sediments. Very little is known about the natural diets and trophic biology of deep-sea nematodes, but enrichment experiments can shed light on nematode feeding selectivity and trophic position. An in-situ pulse-chase experiment (Feedex) was performed in the Nazaré Canyon on the Portuguese margin in summer 2007 to study nematode feeding behaviour. ¹³C-labelled diatoms and bacteria were added to sediment cores which were then sampled over a 14-day period. There was differential uptake by the nematode community of the food sources provided, indicating selective feeding processes. ¹³C isotope results revealed that selective feeding was less pronounced at the surface, compared to the sediment subsurface. This was supported by a higher trophic diversity in surface sediments (Θ⁻¹ = 3.50 ± 0.2) compared to the subsurface (2.78 ± 0.6), implying that more food items may be used by the nematode community at the sediment surface. Predatory and scavenging nematodes contributed relatively more to biomass than other feeding types and can be seen as key contributors to the nematode food web at the canyon site. Non-selective deposit feeding nematodes were the dominant trophic group in terms of abundance and contributed substantially to total nematode biomass. The high levels of ‘fresh’ (bioavailable) organic matter input and moderate hydrodynamic disturbance of the canyon environment lead to a more complex trophic structure in canyon nematode communities than that found on the open continental slope, and favours predator/scavengers and non-selective deposit feeders.     

Effects of sediment-bound Cd, Pb, and Ni on the growth, feeding, and survival of Capitella sp. I

Anthropogenic metal pollutants bioaccumulated in benthic animals by means of feeding and osmotic diffusion. These metals may affect the physiology of the benthos. In this study, we exposed Capitella sp. I to three metals (Cd, Pb, and Ni), each in eight different concentrations, to determine the effects of metals on the animals. Growth rate, ingestion rate, and percent survival were estimated in three separated experiments. The growth and feeding of the worms were sensitive to even the lowest concentrations of each metal added to the sediments. The lowest observable adverse effect levels for Cd, Ni, and Pb were 0.03, 1.59, and 0.41 μmol g^− 1 sediment, respectively. Growth rates in the elevated metal contaminant treatments decreased drastically at slightly contaminated levels, lessened detrimental effects at moderately contaminated levels, and showed incompensable intoxication at heavily contaminated levels. The trends in ingestion rates were similar to those of growth rates. No significant difference in survivorship was found among the different contaminant levels for any of the three heavy metals. Capitella sp. I was most sensitive to Cd, followed by Ni and Pb, which had similar effects. The rapid physiological responses of Capitella sp. I allowed the animals to survive metal exposure. Sediment productivity remained unchanged at different contamination levels of Ni and Pb, but was drastically reduced at 4.75 μmol g^− 1 Cd in the sediment. This further demonstrated Capitella sp. I can adjust their ingestion rates to maintain constant sediment productivities in moderate pollution conditions; however, when threshold concentration was exceeded, homeostasis collapsed.     

Sediment-associated cues for larval settlement of the infaunal spionid polychaetes Polydora cornuta and Streblospio benedicti

Do patchy distribution patterns of infaunal polychaetes result from active site selection of larvae influenced by sediment-associated microbial cues? This hypothesis was tested with still-water laboratory settlement assays revealing the acceptance or rejection of polychaete larvae to qualitatively different sediments. Laboratory brood cultures of the spionid polychaetes Polydora cornuta and Streblospio benedicti yielded a sufficient number of larvae with planktotrophic development for bioassays. High settlement rates (75-95%) of test larvae were observed in response to natural sediment. Sterilization of natural sediment significantly decreased settlement of P. cornuta (25-55%) while combustion of sediment significantly decreased the settlement rate in both species (5-50%). Differences in settlement responses to sediments treated by sterilization or combustion most likely resulted from a variety of factors such as modified sediment fabric, grain size distribution and quantity of adsorbed organic matter. To experimentally address the potential role of microorganisms and microbial metabolites as mediators of larval settlement, ashed sediment was inoculated with viable microorganisms obtained from natural sediment. In both polychaete species, this treatment significantly increased larval settlement in comparison to the control of ashed sediment indicating that larval settlement was at least partially mediated by the presence of microorganisms associated with sediment.     

Laboratory experiments on the effects of variable suspended sediment concentrations on the ecophysiology of the porcelain crab Petrolisthes elongatus (Milne Edwards, 1837)

The porcelain crab Petrolisthes elongatus is a particulate suspension feeding species common to coastal areas of New Zealand (NZ). Consistent with the responses of other suspension feeding species, it is likely to be negatively influenced by elevated suspended sediment concentrations. Laboratory experiments were conducted to quantify the effect of temperature (12 °C, 15 °C and 18 °C) and suspended sediment concentration (total particulate matter (TPM): low < 100 mg L^− 1; medium 100-1000 mg L^− 1; high > 1000 mg L^− 1) on the clearance rate (CR in L h^− 1), oxygen uptake rate (VO₂ in mL h⁻¹), net absorption efficiency (AE), and net energy budget (NEB in J h^− 1) of P. elongatus across a range of sizes. Variation in CR and AE was independent of temperature and of body size, but were significantly different (P < 0.05) at low and medium suspended sediment concentrations compared with high suspended sediment concentrations. CR responded in a non-linear manner to changes in TPM, increasing with TPM up to a maximum value at medium-low concentrations (approximately 250 mg L^− 1) and then decreasing thereafter. CR had almost completely shut down at TPM concentrations of > 1000 mg L^− 1 and at particulate organic matter (POM) concentrations of > 250 mg L^− 1. AE was zero at approximate TPM and POM values of 1200 mg L^− 1 and 300 mg L^− 1, respectively. VO₂ was positively correlated with body size and with temperature, but was independent of TPM. NEB values for P. elongatus were low (approx 110 J g^− 1 h^− 1) at low sediment concentrations, were high (approx 320 J g^− 1 h^− 1) at medium sediment concentrations, and were negative (approx − 114 J g^− 1 h^− 1) at high sediment concentrations. These findings indicate that P. elongatus is likely to be food-limited at sediment concentrations of < 100 mg L^− 1, and severely negatively affected at sediment concentrations of > 1000 mg L^− 1, at least for the duration of such events which may persist for 2-3 days in coastal environments where this crab occurs.     

Sediment (grain size and clay mineralogy) and organic matter quality control on living benthic foraminifera

The paleoecological interpretation of fossil foraminiferal assemblages depends on an understanding of the ecological processes operating at the present. This study investigates both the quality of organic matter (OM) by elemental analysis as well as the sediment grain size and clay mineralogy to understand their relative influence on distribution and abundance of benthic foraminifera. This study is carried out on 15 samples regularly spaced from the mudflat to the tidal marsh. The results indicate that grain size is the most limiting parameter. Living (stained) benthic foraminiferal density and species richness are both very low within coarser sediments. OM is the second limiting factor. The density of foraminifera is the lowest and the species richness is the highest with the lowest organic carbon (C_org) contents and C/N < 12. Conversely, when the C_org is very high and C/N > 12, the density is high and the species richness medium. A high smectite proportion within the clay-size fraction seems to favor the development of Miliammina fusca. Trochammina inflata and Jadammina macrescens are both favored by an increase of organic carbon proportion but Trochammina inflata preferentially feeds on algal-derived OM when compared with Jadammina macrescens.     

Association between osteoporosis and polymorphisms of the bone Gla protein, estrogen receptor 1, collagen 1-A1 and calcitonin receptor genes in Turkish postmenopausal women

In this study, we have investigated the association between osteoporosis and osteocalcin (BGLAP) − 298 C>T, estrogen receptor 1 (ER1) 397 T>C, collagen type1 alpha 1 (Col1A1) 2046 G>T and calcitonin receptor (CALCR) 1340 T>C polymorphisms. Genomic DNA was obtained from 266 persons (158 osteoporotic and 108 healthy controls). Genomic DNA was extracted from EDTA-preserved peripheral venous blood of patients and controls by a salting-out method and analyzed by PCR-RFLP. As a result, there was no statistically significant difference in the genotype and allele frequencies of patients and controls for BGLAP − 298 C>T, Col1A1 2046 G>T, ER1 397 T>C and CALCR 1340 T>C polymorphisms. However, ER1 CC genotype compared with TT + TC genotypes was found to increase the two fold the risk of osteoporosis [p = 0.039, OR = 2.156, 95% CI (1.083–4.293)] and CALCR CC genotype compared with TT + TC genotypes was found to have protective effect against osteoporosis [p = 0.045, OR = 0.471, 95% CI (0.237–0.9372)]. In the combined genotype analysis, ER1/CALCR TCCC combined genotype was estimated to have protective effect against osteoporosis [p = 0.0125, OR = 0.323, 95% CI (0.1383–0.755)] whereas BGLAP/Col1A1 CCTT and ER1/CALCR CCTT combined genotypes were estimated as risk factors for osteoporosis in Turkish population (p = 0.027, p = 0.009 respectively).     

Chromosomal rearrangements associated with pelagic larval duration in Labridae (Perciformes)

The family Labridae is one of the largest and most important groups of reef fishes in the Southern Atlantic. There is a remarkable ecologic interest in this family because of their complex interactions in the reef environment. Predictions of genetic variability in fish based on biological patterns have often been contradictory. The present work aimed to increase the cytogenetic data about the family and verify the possible correlation between larval pelagic phase and chromosomal rearrangements based on the putative basal Perciformes karyotype (2n = 48a). Therefore, cytogenetic analyses were performed in the species Halichoeres brasiliensis (2n = 48, 48a, FN = 48); Halichoeres radiatus (2n = 48, 48a, FN = 48) and in three populations of Halichoeres poeyi (2n = 48, 4m + 44st-a, FN = 52) from Brazilian coastline. A conserved diploid number was observed in all species and populations. Single NORs were identified in H. brasiliensis and in two populations of H. poeyi (BA and RJ), while multiple NORs were observed in H. radiatus and in H. poeyi from Rio Grande do Norte. The constitutive heterochromatin is reduced and distributed over centromeric and pericentromeric regions. The ribosomal sites allowed differentiating two groups of H. poeyi along the Brazilian coast; one of them comprising the population from RN, bearing multiple NORs, and another representing the populations from BA and RJ, bearing single NORs. The recently separated species, H. brasiliensis and H. radiatus, although presenting similar diploid numbers and chromosomal formulae, could be distinguished by the number of NOR-bearing chromosomes. The results revealed an evolutionary pattern chiefly derived from pericentric inversions. The correlation between larval pelagic phase and cytogenetic data on Labridae indicates that the degree of karyotypic diversification reported within this family, ranging from a highly conserved to a derived pattern, is probably influenced by the species-specific duration of larval pelagic phase.     

Effect of temperature on phosphorus sorption to sediments from shallow eutrophic lakes

The availability of phosphorus (P) in lakes is dependent on the sorption characteristics of the underlying sediments. Temperature is a crucial factor affecting the P sorption in sediments. The objective of this study was to evaluate the effect of temperature on sorption of P by sediments from two eutrophic lakes. The study was carried out using short-term batch experiments at 4, 20 and 30 °C. Phosphorus sorption kinetics, isotherms, fractionation and desorption were investigated. The P sorption was dependent on sediment type and temperature (p < 0.001). The Mei sediments showed a higher sorption rate and sorption capacity than Hua sediments. The P sorption kinetics were best described by a pseudo second order model (R² > 0.97). Activation energies derived from the kinetics rate constant indicated that P sorption onto the two sediments was controlled by a diffusion process. For both sediments, Freundlich model fit the P sorption isotherms well and the calculated apparent sorption heat was 6.37 kJ mol⁻¹ for Mei sediments and 8.67 kJ mol⁻¹ for Hua sediments. This indicated that P sorption onto both sediments was endothermic. Adding P significantly increased the soluble and loosely bound P (S/L-P), aluminum-bound P (Al-P) and iron-bound P (Fe-P) (p < 0.05). The amount of Al-P and Fe-P was markedly higher at 30 °C than at 4 °C (p < 0.05). Subsequent P desorption indicated that adsorbed P was highly labile, in particular for Hua sediment. The degree of P mobility that occurred during sediment sorption was inversely related to the temperature at the time of sorption. A significant relationship (R² = 0.978) between phosphorus sorption maximum and oxalate-extractable Fe and Al at different temperatures reflects that the amorphous contents of Fe and Al are responsible for the temperature effect on P sorption.     

Simultaneous study of particle reworking, irrigation transport and reaction rates in sediment bioturbated by the polychaetes Heteromastus and Marenzelleria

The present study employed simultaneously methods to investigate particle and solute transport and reaction rates in sandy sediments inhabited by two worms (2500 m^− 2) with different feeding modes. Heteromastus filiformis is a head-down deposit-feeder and the main activities exerted by this worm are transport of particles as faecal pellets from subsurface to surface sediments and burrow ventilation. Marenzelleria viridis is a surface deposit-feeder that actively searches for food by burrowing near the sediment surface, producing a network of ventilated galleries in this zone. M. viridis exhibited 1.5 to 2.2 times higher particle mixing rates (D_b = 3.3 to 4 × 10^− 3 cm^− 2 d^− 1) compared to H. filiformis. In M. viridis treatments, continuous advection (eddy diffusion) was the major factor influencing solute transport resulting in apparent diffusion rates (D_a = 2.2 cm^− 2 d^− 1), which were 3 times higher than molecular diffusion within the sediment. In H. filiformis inhabited sediments, the transport of solutes was discontinuous and driven by a surprisingly high nonlocal exchange (α = 1.1-1.3 d^− 1), emphasizing its strong irrigation effects. Accordingly, the enhancement of solute fluxes was more pronounced for H. filiformis compared to M. viridis. Depth integrated TCO₂ production derived from diagenetic modelling, which takes into account three reaction zones, is in good agreement with rates obtained from measured fluxes, indicating the applicability of both approaches to get reliable rates. However, the reaction rates showed that the presence of animals had a modest effect on microbial carbon oxidation. The results proved that transport conditions are deeply related to feeding modes. Exchange of solutes was the most important transport process by H. filiformis, while M. viridis affected both mixing and solute transport.     

In vitro cytotoxicity of melleolide antibiotics: structural and mechanistic aspects

Melleolide sesquiterpene aryl esters are secondary products of the mushroom genus Armillaria. We compared the cytotoxicity of eleven melleolides—five thereof are new natural products—against four human cancer cell lines. Armillaridin, 4-O-methylarmillaridin, and dehydroarmillylorsellinate were most active, at IC₅₀ = 3.0, 4.1 and 5.0 μM, respectively, against Jurkat T cells for the former two compounds, and K-562 cells for the latter. Dehydroarmillylorsellinate did not inhibit respiration and RNA-synthesis of K-562 cells at 5 μM. However, replication of DNA dropped to 35% after 120 min at this concentration, and translational activity also decreased.     

Effects of experimental harvesting on recruitment of an alien mussel Mytilus galloprovincialis

Successful fisheries management is underpinned by an understanding of the processes that underlie the population dynamics of exploited stocks. This study considered the effects of experimental harvesting on recruitment of Mytilus galloprovincialis along the west coast of South Africa, where harvesting of this alien species is being contemplated. In particular, the role of settlement habitat availability in the form of adult mussels was analysed. To track the effects of a spectrum of harvesting intensities, five treatments were implemented: F = 0 (i.e. a control), F = 0.3, F = 0.6, F = 0.9 and F = 1. At these harvesting intensities 0%, 30%, 60%, 90% or 100% of mussel biomass was removed respectively at the outset of the experiment. A significant negative exponential relationship (p < 0.01) was found between M. galloprovincialis recruit density and harvesting intensity, with intensities greater than F = 0.3 dramatically reducing recruitment. This pattern was recorded throughout the intertidal zone and remained temporally constant over 2 years. Significant positive linear relationships (p < 0.01) between recruit density and adult mussel biomass or density indicate a strong correlation between availability of settlement habitat and recruitment. It is likely that the high recruit density recorded at low harvesting intensities (2000-20 000 per 0.01 m²) exceeds the level required for population maintenance. However, if settlement habitat is eliminated or significantly reduced, as was achieved by F = 0.3 or above, recruitment may become limiting. Thus, to protect stock replenishment, harvesting of M. galloprovincialis in this region should take place at intensities less than F = 0.3.     

Induction of metamorphosis in the Asian shore crab Hemigrapsus sanguineus: Characterization of the cue associated with biofilm from adult habitat

Recruitment of crabs to nursery habitat requires settlement of the megalopal stage on suitable substratum followed by metamorphosis into the first juvenile stage. Reducing the time to metamorphosis may result in higher recruitment and survival. Previous work has shown that metamorphosis of the Asian shore crab is accelerated by cues from three different sources: (a) water-soluble exudate produced by conspecific adult crabs; (b) biofilm covering rocks in natural habitat for this species; and (c) abiotic rock from natural habitat. The objective of the present investigation was to characterize the metamorphic cue associated with biofilm from rocky intertidal habitat and to compare the three metamorphic cues (exudate from conspecific adults, biofilm from rocky intertidal, and texture of substratum) that have been identified for H. sanguineus. Results of our study show that megalopae of the Asian shore crab respond strongly to biofilm associated with rocky intertidal habitat that has developed for at least 8 days. We also found that megalopae respond to textured rock surfaces from natural habitat, even when those surfaces had been rendered abiotic. The cue remains active after the biofilm has been exposed to − 20 ºC for 12 h, but is de-activated by a few minutes exposure to 100 °C. Moreover, the biofilm cue appears to work in synergy with cues from other sources, but requires actual contact with the biofilm. Our findings show that addition of biofilm to an abiotic textured rock surface significantly decreases mean time to metamorphosis, and simultaneous exposure of megalopae to biofilm-covered rock and to exudate from adult H. sanguineus decreases mean time to metamorphosis even further. The response of this species to multiple cues—and particularly to biofilm in the absence of adult conspecifics—provides a clear advantage in the colonization of virgin habitat and helps explain the very rapid spread of this invasive species along the majority of the east coast of the United States in only two decades.     

Introducing transglycosylation activity in Bacillus licheniformis α-amylase by replacement of His235 with Glu

To understand the role of His and Glu in the catalytic activity of Bacillus licheniformis α-amylase (BLA), His235 was replaced with Glu. The mutant enzyme, H235E, was characterized in terms of its mode of action using labeled and unlabeled maltooctaose (Glc8). H235E predominantly produced maltotridecaose (Glc13) from Glc8, exhibiting high substrate transglycosylation activity, with K_m = 0.38 mM and k_cat/K_m = 20.58 mM⁻¹ s⁻¹ for hydrolysis, and K_m2 = 18.38 mM and k_cat2/K_m2 = 2.57 mM⁻¹ s⁻¹ for transglycosylation, while the wild-type BLA exhibited high hydrolysis activity exclusively. Glu235—located on a wide open groove near subsite +1—is likely involved in transglycosylation via formation of an α-1,4-glycosidic linkage and may recognize and stabilize the non-reducing end glucose of the acceptor molecule.     

Chloroplast DNA variation and phylogeographic patterns in the Chinese endemic marsh herb Sagittaria potamogetifolia

We examined chloroplast DNA (cpDNA) atpB–rbcL intergenic spacer sequences variation within Sagittaria potamogetifolia, an endangered and endemic marsh herb in China. Sequence data were obtained from 54 individuals in six extant populations of the species. Sequences appeared to evolve neutral (Tajima's criterion D = −1.59826, 0.1 > P > 0.05 and Fu and Li's tests D* = −1.44484, P > 0.1; F* = −1.83446, P > 0.1). Eleven haplotypes were identified in S. potamogetifolia. A relatively high level of haplotype diversity (h = 0.0.699) and low level of nucleotide diversity (pi = 0.0035 ± 0.0020) were detected in S. potamogetifolia. Pairwise comparisons of F_st and Nm deduced from cpDNA variation suggested no significant genetic differentiation between populations of S. potamogetifolia excepted for the WY-1 population. Low genetic differentiation among populations and also among regions was consistently indicated by both hierarchical analyses of molecular variance (AMOVA) and the structure of a neighbor-joining tree. Lack of population differentiation between populations or between regions in cpDNA sequences may be due to effects of lower substitution rates or lineage sorting. In the minimum spanning network, all tip haplotypes except for the haplotype J were unique to a particular population, while the interior nodes except for the haplotype E were widespread (haplotype A). From nested clade analysis (NCA), the evolutionary events such as restricted gene flow with isolation by distance and allopatric fragmentation were inferred to responsible for the current distribution of S. potamogetifolia populations, as well as their genetic diversity.