Cytogenetic characterisation of the razor shells Ensis directus (Conrad, 1843) and E. minor (Chenu, 1843) (Mollusca: Bivalvia)

The European razor shell Ensis minor (Chenu 1843) and the American E. directus (Conrad 1843) have a diploid chromosome number of 38 and remarkable differences in their karyotypes: E. minor has four metacentric, one metacentric–submetacentric, five submetacentric, one subtelocentric and eight telocentric chromosome pairs, whereas E. directus has three metacentric, two metacentric–submetacentric, six submetacentric, six subtelocentric and two telocentric pairs. Fluorescent in situ hybridisation (FISH) using a major ribosomal DNA probe located the major ribosomal genes on one submetacentric chromosome pair in both species; FISH with a 5S ribosomal DNA (5S rDNA) probe rendered one chromosomal (weak) signal for E. minor and no signal for E. directus, supporting a more dispersed organisation of 5S rDNA compared to the major ribosomal genes. The vertebrate telomeric sequence (TTAGGG) _n was located on both ends of each chromosome, and no interstitial signals were detected. In this work, a comparative karyological analysis was also performed between the four Ensis species analysed revealing that the three European species studied so far, namely E. minor, E. siliqua (Linné 1758) and E. magnus Schumacher 1817 show more similarities among them than compared to the American species E. directus. In addition, clear karyotype differences were found between the morphologically similar species E. minor and E. siliqua.     

Comparison of power output by rice (Oryza sativa) and an associated weed (Echinochloa glabrescens) in vascular plant bio-photovoltaic (VP-BPV) systems

Vascular plant bio-photovoltaics (VP-BPV) is a recently developed technology that uses higher plants to harvest solar energy and the metabolic activity of heterotrophic microorganisms in the plant rhizosphere to generate electrical power. In the present study, electrical output and maximum power output variations were investigated in a novel VP-BPV configuration using the crop plant rice (Oryza sativa L.) or an associated weed, Echinochloa glabrescens (Munro ex Hook. f.). In order to compare directly the physiological performances of these two species in VP-BPV systems, plants were grown in the same soil and glasshouse conditions, while the bio-electrochemical systems were operated in the absence of additional energy inputs (e.g. bias potential, injection of organic substrate and/or bacterial pre-inoculum). Diurnal oscillations were clearly observed in the electrical outputs of VP-BPV systems containing the two species over an 8-day growth period. During this 8-day period, O. sativa generated charge ～6 times faster than E. glabrescens. This greater electrogenic activity generated a total charge accumulation of 6.75?±?0.87 Coulombs for O. sativa compared to 1.12?±?0.16 for E. glabrescens. The average power output observed over a period of about 30 days for O. sativa was significantly higher (0.980?±?0.059 GJ?ha^?1?year^?1) than for E. glabrescens (0.088?±?0.008 GJ?ha^?1?year^?1). This work indicates that electrical power can be generated in both VP-BPV systems (O. sativa and E. glabrescens) when bacterial populations are self-forming. Possible reasons for the differences in power outputs between the two plant species are discussed.     

Eisenia arborea J.E. Areschoug as abalone diet on an IMTA farm in Baja California,México

Recent progress in the domestication of Eisenia arborea lead us to test this species as an alternative to feed red abalone (Haliotis rufescens) instead of Macrocystis pyrifera, which is the main seaweed used to feed farmed abalone in Baja California, Mexico. E. arborea is the kelp with the largest and most southerly latitudinal distribution on the North Pacific East Coast capable of growing at higher temperatures and in relatively low nutrient conditions. The availability of M. pyrifera is frequently uncertain because it is strongly affected by El Niño events. In order to test E. arborea as a diet for farmed abalone, animals of two different sizes (6 and 2 cm) were fed separately for 12 months with these two seaweed species. The abalones were cultured in cages in an integrated multi-trophic aquaculture farm within San Quintín Bay, Baja California, Mexico. Seaweed was collected for chemical analysis, and every 3 months, animals were measured and weighed to estimate growth. Small size abalone doubled their size on both diets, with an average increase in length of 2.2 mm month^?1. No significant differences were observed between both treatments. Large abalone fed with M. pyrifera had slighter higher growth rates compared to those fed with E. arborea (0.57 and 0.50 % day^?1, respectively). Although M. pyrifera appeared to be a better diet for large animals, the growth rates obtained with E. arborea and the fact that this species could be cultivated in warmer conditions makes this seaweed species a good candidate to feed farmed abalone.     

Growth of European eel Anguilla anguilla along the southern Baltic coast of Germany and implication for the eel management

To detect growth differences of European eel Anguilla anguilla along the southern German Baltic coast 728 yellow eels, with total lengths ranging from 256 to 944 mm and ages ranging from 3 to 15 years were collected from six coastal areas from 2005 to 2009. The estimation of the growth performance was based on the otolith increments. The mean growth rate of the female yellow eels varied from 56 to 62 mm?year^–1. No significant differences in the mean growth rate were detected between eels from inner and open coastal areas. The overall mean annual increment of eels was estimated at 59 mm?year^?1. Specific growth rates (SGR) of female yellow eels decreased with increasing age from 0.68 %?day^?1 in the first year to 0.05 %?day^?1 in the tenth year. Results indicate that no separation is needed in the development of population models or management initiatives based on the growth performance of eel in inner and open coastal waters of the southern German Baltic coast.     

Production of Excirolana armata (Dana, 1853) (Isopoda, Cirolanidae) on an exposed sandy beach in southeastern Brazil

The somatic and gonad productions of the cirolanid isopod Excirolana armata were analyzed by taking monthly samples from December 2003 to November 2005 on Una beach, S?o Paulo state (24°S), southeastern Brazil. Sampling was performed along three fixed transects established from the base of the foredunes to the waterline. Weight-specific growth rate was used to estimate the E. armata somatic production for 2004 and 2005, separately. The gonad production was estimated based on the monthly reproductive potential (mean number of eggs/embryos per female × monthly abundance of ovigerous females with near-release broods) for 2004. The annual somatic production of E. armata population varied from 15.57 to 17.25?g AFDW m^?1?year^?1 and the somatic production/biomass ratio (P _s/B) from 3.55 to 3.14?year^?1 for 2004 and 2005, respectively. The P _s/B ratios were higher for males (4.02 and 3.19?year^?1 for 2004 and 2005) than for females (3.10?year^?1 for both years). The annual gonad production (P _g?=?1.07?g AFDW m^?1?year^?1) contributed about 15 and 6% to the total production (P _s?+?P _g) of females and the population, respectively. The proportion of gonad to somatic production of females (P _g/P _s) increased with individual size (ca 90% in the 7.5?mm size class), and the annual weight-specific gonad production (P _g/B ratio) was estimated to 0.24?year^?1. The high P _s/B ratios estimated for E. armata derive from the fast growth of individuals and show the importance of this population to the energy flow on Una beach ecosystem. However, the low percentage of juveniles verified in this population and in other studies of populations of the genus Excirolana is discussed as an important source of underestimation of P _s/B ratio.     

Recolonization of vascular epiphytes in a shaded coffee agroecosystem

Aim: Shaded coffee plantations constitute an important refuge for biodiversity. Despite the fact that epiphytic plants form a significant component of these agroecosystems, their removal from the shade trees is commonplace in Latin America. To what extent does the epiphyte community recover from this severe disturbance? Location: Shaded coffee agroecosystem in Veracruz, Mexico (19°28′03″ N, 96°55′58″ W; 1200 m asl). Methods: We assessed the diversity, biomass and recolonization patterns of vascular epiphytes in shade trees, 8‐9 yr after complete epiphyte removal (E^?), and in control ‘non‐removal’ sites (E⁺). In order to evaluate the effects of prior epiphyte removal, all vascular epiphytes were completely removed from 10 trees per treatment (E^? and E⁺); all epiphyte species collected were identified and dry biomass measured. Results: Eight to nine years after removal, epiphyte biomass in the E^? shade trees was 35% of that found in the control sites. A total of 55 epiphyte species, belonging to 12 families, were registered; 40 in E^?, and 48 in E⁺. Six species belonging to Bromeliaceae, Orchidaceae, Cactaceae and Araceae accounted for 75% of the biomass in E⁺ while six species of bromeliads accounted for 76% of the biomass in E^?. Some bromeliads proliferated following disturbance; however, ferns showed lower recovery. Conclusions: Epiphyte community recovery, in terms of biomass and diversity, is considerably higher in the coffee plantation than has been previously reported for other tropical ecosystems. Epiphyte recolonization patterns reflected both the abundance of species in the surrounding matrix and certain species‐specific traits. For such agroecosytems to function as effective reservoirs of epiphyte diversity, epiphyte stripping should be avoided.     

Voltage dependent potassium fluxes and the significance of action potentials in Acetabularia

Membrane potential, V_m, and K⁺(⁸⁶Rb⁺) fluxes have been measured simultaneously on individual cells of Acetabularia mediterranea. During resting state (resting potential approx. ?170 mV) the K⁺ influx amounts to 0.24–0.6 pmol · cm^?2 · s^?1 and the K⁺ efflux to 0.2–1.5 pmol · cm^?2 s^?1. According to the K⁺ concentrations inside and outside the cell (40 : 1) the voltage dependent K⁺ flux (zero at V_m = E_K = ?90 mV) is stimulated approx. 40-fold for V_m more positive than E_K.It is calculated that during one action potential (temporary depolarization to V_m more positive than E_K) a cell looses the same amount of K⁺, which leaks in during 10–20 min in the resting state (V_m = ?170 mV). Since action potentials occur spontaneously in Acetabularia, they are therefore suggested to have a significant function for the K⁺ balance of this alga.     

Mössbauer, EPR, and MCD studies of the C9S and C42S variants of Clostridium pasteurianum rubredoxin and MCD studies of the wild-type protein

Rubredoxins contain a mononuclear iron tetrahedrally coordinated by four cysteinyl sulfurs. We have studied the wild-type protein from Clostridium pasteurianum and two mutated forms, C9S and C42S, in the oxidized and reduced states, with Mössbauer, integer-spin EPR, and magnetic circular dichroism (MCD) spectroscopies. The Mössbauer spectra of the ferric C42S and C9S mutant forms yielded zero-field splittings, D=1.2?cm^?1, that are about 40% smaller than the D-value of the wild-type protein. The ⁵⁷Fe hyperfine coupling constants were found to be ca. 8% larger than those of the wild-type proteins. The present study also revealed that the ferric wild-type protein has δ=0.24±0.01?mm/s at 4.2?K rather than δ=0.32?mm/s as reported in the literature. The Mössbauer spectra of both dithionite-reduced mutant proteins revealed the presence of two ferrous forms, A and B. These forms have isomer shifts δ=0.79?mm/s at 4.2?K, consistent with tetrahedral Fe²⁺(Cys)₃(O-R) coordination. The zero-field splittings of the two forms differ substantially; we found D=?7±1?cm^?1, E/D=0.09 for form A and D=+6.2±1.3?cm^?1, E/D=0.15 for form B. Form A exhibits a well-defined integer-spin EPR signal; from studies at X- and Q-band we obtained g _z =2.08±0.01, which is the first measured g-value for any ferrous rubredoxin. It is known from X-ray crystallographic studies that ferric C42S rubredoxin is coordinated by a serine oxygen. We achieved 75% reduction of C42S rubredoxin by irradiating an oxidized sample at 77?K with synchrotron X-rays; the radiolytic reduction produced exclusively form A, suggesting that this form represents a serine-bound Fe²⁺ site. Studies in different buffers in the pH?6–9 range showed that the A:B ratios, but not the spectral parameters of A and B, are buffer dependent, but no systematic variation of the ratio of the two forms with pH was observed. The presence of glycerol (30–50% v/v) was found to favor the B form. Previous absorption and circular dichroism studies of reduced wild-type rubredoxin have suggested d-d bands at 7400, 6000, and 3700?cm^?1. Our low-temperature MCD measurements place the two high-energy transitions at ca. 5900 and 6300?cm^?1; a third d-d transition, if present, must occur with energy lower than 3300?cm^?1. The mutant proteins have d-d transitions at slightly lower energy, namely 5730, 6100?cm^?1 in form A and 5350, 6380?cm^?1 in form B.     

Distribution, standing stock, growth, mortality and production of Strongylocentrotus pallidus (Echinodermata: Echinoidea) in the northern Barents Sea

The regular sea urchin, Strongylocentrotus pallidus (G.O. Sars, 1871), is a widespread epibenthic species in high-Arctic waters. However, little is known about its distribution, standing stock, population dynamics and production. In the northern Barents Sea, S. pallidus was recorded on seabed still photographs at 10 out of 11 stations in water depths of 80–360?m. Mean abundances along photographic transects of 150–300 m length ranged between <0.1 and 14.7?ind. m^?2 yielding a grand average of 3.6?ind.?m^?2. The small-scale distribution along the transects was patchy, with densities varying from nil to an overall maximum of 25.5 ind. m^?2, and exhibited a significant relation to the number of stones present. Sea urchin test diameters, measured on scaled photographs, extended from 7 to 90?mm. Median values at single stations varied from 14 to 46?mm, showing a significant inverse relationship to water depth. Biomass, estimated by combining photographic abundances, size frequencies and a size-mass function established with trawled specimens, ranged between <0.1 and 3.0?g ash-free dry mass m^?2, averaging about 1.0?g ash free dry mass m^?2. An analysis of skeletal growth bands in genital plates was carried out with 143 trawled individuals ranging in test diameter (D) from 4 to 48?mm. Assuming these bands to represent annual growth marks, the ages of the specimens analysed ranged between 3 and 42 years. A von Bertalanffy function was fitted to size-at-age data to model individual growth pattern (D_∞?=?102.3?mm, k?=?0.011 year^?1, t₀?=?0.633?year). The annual mortality rate Z of the population in the northern Barents Sea was estimated from a size-converted catch curve to be 0.08 year^?1. Applying the weight-specific growth rate method, the average P/B ratio and the mean annual production of this population were estimated as 0.07 year^?1 and 0.076?g AFDM m^?2 year^?1, respectively. In conclusion, S. pallidus is characterized by slow growth, low mortality, high longevity and low productivity. Because of its relatively high biomass, it is considered to contribute significantly to total benthic standing stock and carbon flux in the study area.     

Occurrence and Identification of Yeast Species in Fermented Liquid Feed for Piglets

The major objective of the present study was to investigate the occurrence and identity of yeast species in fermented liquid feed (FLF) used for feeding piglets. In total, 40 different Danish farms were included in the analysis. The preparation and composition of FLF was found to be very heterogeneous with high variations in both yeast counts and yeast species composition. The yeast population varied between 6.0?×?10³ and 4.2?×?10⁷?cfug^?1 with an average yeast count of 8.7?×?10⁶?±?1.1?×?10⁷?cfug^?1. A total of 766 yeasts were isolated and identified by conventional and/or molecular typing techniques. The predominant yeast species in the FLF samples were found to be Candida milleri (58.4%), Kazachstania exigua (17.5%), Candida pararugosa (6.40%) and Kazachstania bulderi (5.09%). No clear separation between isolates of C. milleri and Candida humilis could be obtained based on sequencing of the D1/D2 region of the 26S rRNA gene. The combined use of ITS-RFLP analysis and phenotypic criteria did meanwhile suggest a closer relationship with C. milleri than C. humilis.     

Energetics of the one-electron reduction steps of riboflavin,FMN and FAD to their fully reduced forms

The one-electron reduction potentials (E¹₇) of riboflavin, FMN and FAD have been determined using pulse radiolysis from the position of the electron-transfer equilibria between flavins and reference quinones in aqueous solution. The average value for all three flavins E¹₇(F/FH^.) = ? 314 ± 8 mV is used to calculate the second-electron reduction potential of the flavins E²₇(FH^./FH₂(FH^?)) = ? 124 mV.     

Oxidation-reduction properties of the electron acceptors of Photosystem II. II. Redox titration at various pH values of the flash-induced formation of C550 in Chlamydomonas Photosystem II particles lacking the secondary quinone electron acceptor

Redox titrations of the flash-induced formation of C550 (a linear indicator of Q^?) were performed between pH 5.9 and 8.3 in Chlamydomonas Photosystem II particles lacking the secondary electron acceptor, B. One-third of the reaction centers show a pH-dependent midpoint potential (E_m,7.5) = ? 30 mV) for redox couple $\text{Q}\text{Q}{}^{\mathrm{?}}$, which varies by ?60 mV/pH unit. Two-thirds of the centers show a pH-independent midpoint potential (E_mm = + 10 mV) for this couple. The elevated pH-independent E_m suggests that in the latter centers the environment of Q has been modified such as to stabilize the semiquinone anion, Q^?. The midpoint potentials of the centers having a pH-dependent E_m are within 20 mV of those observed in chloroplasts having a secondary electron acceptor. It appears therefore that the secondary electron acceptor exerts little influence on the E_m of $\text{Q}\text{Q}{}^{\mathrm{?}}$. An EPR signal at g 1.82 has recently been attributed to a semiquinone-iron complex which comprises Q^?. The similar redox behavior reported here for C550 and reported by others (Evans, M.C.W., Nugent, J.H.A., Tilling, L.A. and Atkinson, Y.E. (1982) FEBS Lett. 145, 176–178) for the g 1.82 signal in similar Photosystem II particles confirm the assignment of this EPR signal to Q^?. At below ?200 mV, illumination of the Photosystem II particles produces an accumulation of reduced pheophytin (Ph^?). At ?420 mV Ph^? appears with a quantum yield of 0.006–0.01 which in this material implies a lifetime of 30–100 ns for the radical pair P-680⁺Ph^?.     

Bioaccumulation of Trace Mercury in Trophic Levels of Benthic, Benthopelagic, Pelagic Fish Species, and Sea Birds from Arvand River, Iran

In this study, concentration of mercury was determined in the trophic levels of benthic, benthopelagic, pelagic fish species, and river birds from Arvand River, located in the Khuzestan province in the lowlands of southwestern Iran at the head of the Persian Gulf. The order of mercury concentrations in tissues of the fish species was as follows: liver>gill>muscle and in tissues of the kingfisher species was as follows: feather>liver>kidney>muscle. Therefore, liver in fish and feather in kingfisher exhibited higher mercury concentration than the other tissues. There was a positive correlation between mercury concentrations in fish and kingfisher species with size of its food items. We expected to see higher mercury levels in tissues of female species because they are larger and can eat larger food items. The results of this study show that the highest mean mercury level were found in the kingfisher (Anas crecca), followed by benthic (Epinephelus diacanthus), benthopelagic (Chanos chanos), and pelagic fish (Strongylura strongylura). Mean value of mercury in fish species, S. strongylura were (0.61 μg g^?1 dry weight), C. chanos (0.45 μg g^?1 dry weight), E. diacanthus (0.87 μg g^?1 dry weight), and in kingfisher species A. crecca was (2.64 μg g^?1 dry weight). Significant correlation between mercury concentration in fish and kingfisher may be related to high variability of mercury in the fish.     

Effects of Clostridium butyricum and Enterococcus faecium on growth performance, lipid metabolism, and cecal microbiota of broiler chickens

To investigate the effects of Clostridium butyricum and Enterococcus faecium on the growth performance, lipid metabolism, and cecal microbiota of broilers, 264 one-day-old male Ross 308 broiler chicks were randomly allocated into four treatments with six replicates in a 2?×?2 factorial arrangement and fed four diets with two levels of C. butyricum (0 or 1?×?10⁹ cfu/kg) and two levels of E. faecium (0 or 2?×?10⁹ cfu/kg) for 42 days. There was no significant interaction between C. butyricum and E. faecium on the growth performance, lipid metabolism, and cecal microbiota of broilers. However, broilers supplemented with E. faecium had lower (P?=?0.022) serum leptin level at day 21 and higher (P?<?0.001) fatty acid synthase (FAS), malic enzyme (ME), and acetyl–CoA carboxylase (ACC) mRNA levels in the liver at day 42. Supplementation of C. butyricum improved (P?<?0.05) the average daily feed intake and average daily gain, increased (P?=?0.016) the serum insulin level at 21 days of age, enhanced (P?<?0.05) the content of intramuscular fat, activities of FAS in the liver and lipoprotein lipase (LPL) in the breast muscle, mRNA expression of FAS, ME, and ACC in the liver and LPL in the breast muscle at 42 days of age, but reduced (P?=?0.030) cecal Bacteroidetes relative abundance at 21 days of age. The results of this study indicate that the increased intramuscular fat content of broilers fed C. butyricum as observed may be the result of enhanced lipogenesis.     

Larvae of uncommon caridean decapods in the German Bight: Species composition,distribution and abundance

Typically, the most abundant group of shrimp larvae in the German Bight is formed by representatives of the family Crangonidae. Larvae of the remaining species have been largely ignored, and only scarce information concerning their ecology is available. Thus, the purpose of the present study was to determine the species composition, distribution and abundance of noncrangonid shrimp larvae in the German Bight in July 1990, after the mildest winter of the century. The material is based upon plankton samples collected at 77 stations, covering the entire German Bight. Eight species were identified, as well as larvae of Palaemonidae andProcessa-juveniles.Processa nouveli holthuisi (53.0%) andP. modica (31.3%) were predominant in the collection. The distribution of the two species was clearly separated: the main concentration ofP. nouveli holthuisi (peak concentration of 1.94 larvae per m³) was confined to the northwest corner of the German Bight, while a majority ofP. modica larvae (peak concentration of 0.54 larvae per m³) occurred at the southwesterly stations. The spatial distribution ofCaridion steveni andEualus occultus around Helgoland indicates the presence of an adult population at the only rocky island in the study area. Other taxa, such as larvae of Palaemonidae and juvenilePandalina brevirostris were collected exclusively in estuarine habitats. Based upon both the results of the present study and comparable data, we conclude that developmental stages of ten non-crangonid species, as well as representatives of Palaemonidae, can be expected to occur in the plankton of the German Bight. The extremely mild temperatures of the preceding winter may have been, in part, responsible for the relatively high densities of some taxa encountered during our plankton survey. We assume that warm winter temperatures favour the immigration, reproduction and survival of cold-sensitive species.     

Effect of subcritical water hydrolysate in the brown seaweed Saccharina japonica as a potential antibacterial agent on food-borne pathogens

Seaweeds are rich in bioactive compounds which have well-documented antioxidant properties. They also have antimicrobial activities against food pathogenic microorganisms. This study uses an extract of the brown seaweed, Saccharina (Laminaria) japonica, produced by subcritical water hydrolysis (SWH) for investigating its potential to inhibit bacteria. De-oiled S. japonica was obtained by supercritical carbon dioxide extraction. The reaction temperatures for hydrolysis of raw and de-oiled S. japonica were maintained from 200 to 280 °C. The experiment was done with condition 1.3–6.0 MPa for the reaction pressure and 1:10 (w/v) for the ratio of material to water. The antibacterial activities of raw and de-oiled S. japonica produced by SWH were determined by using the agar diffusion method. Antibacterial activity was tested against two Gram-negative (Escherichia coli and Salmonella typhimurium) and two Gram-positive bacteria (Staphylococcus aureus and Bacillus cereus). The antibacterial activities of hydrolysate water with catalyst at 240 °C showed better bacterial inhibition than the others. Strong antibacterial activity was found using de-oiled material with acetic acid added, with a zone of inhibition of S. typhimurium (14.33?±?0.06 mm) and E. coli (13.00?±?0.09 mm). On the other hand, the weakest antibacterial inhibition was found for S. aureus (12.83?±?0.10 mm) and B. cereus (12.50?±?0.09 mm).     

Notes on growth and behaviour of the American razor clamEnsis directus in the Wadden Sea and the predation on it by birds

Ensis directus (Conrad), a bivalve found in Europe only in the past few years, has filled an empty niche and spread rapidly over the intertidal flats in the Wadden Sea. The growth of the animals was investigated using a few samples taken near Langeness in February 1984. The age of the animals could be determined by reading the clearly visible year marks on the shells. Notwithstanding the low density ofE. directus, some oystercatchers appear to have already specialized in feeding on this new food source.     

Population status of giant clams (Mollusca: Tridacnidae) in the northern Red Sea,Egypt

Throughout their range, giant clams (family Tridacnidae) are increasingly threatened by anthropogenic impacts and natural disasters, but little is known about their population status. In this first assessment of the tridacnid population at Abu Sauatir in the northern Red Sea, a total of 491 m² were surveyed and >200 clams recorded. Tridacna maxima was the only species found. The population's live:dead ratio was 3:1. Overall clam density was 0.08?±?0.008 live and 0.02?±?0.007 dead individuals per 0.25 m². Greatest densities occurred on the reef flat in 1 m depth (live), and on the northern reef slope in deeper waters (dead). On the slope, live clam density decreased significantly, whereas dead clam density increased significantly with depth. Sizes of live and dead individuals differed significantly. Live clams ranged from 1 to 30 cm (median 5 cm). Juveniles ≤2 cm (8.2% of the population) and individuals >11 cm occurred on the reef slope but not on the reef flat. Live clam sizes did not differ significantly between reef sites. Dead clam size ranged from 2 to 15 cm (median 6.5 cm). 2.1% of the empty shells were ≤2 cm long. Dead clam sizes differed significantly between 5 and 10 m depth on the northern reef slope. The low clam abundance (live and dead) in the shallowest and most easily accessible areas of the reef flat, combined with small sizes, strongly suggest artisanal reef-top gathering for meat and shells.     

A scale-dependent approach to study pollution control processes in wetland soils using three different techniques

The Elbe River, Germany, has received heavy metals and arsenic from the discharge of urban industrial, and agricultural effluent. During periods of inundation, these contaminants were transported with water into floodplain ecosystems, where they settled and accumulated predominantly in depressions and low-lying terraces. Markedly elevated arsenic concentration in soil solution during floods exceeded the inspection value of 10 μg L^?1 of the German soil protection ordinance. Highly variable hydrological conditions in floodplains can affect the dynamics of pollutants. The study of processes controlling the dynamics of pollutants is challenging because the results are required to answer both scientific and practical questions regarding protection of groundwater and plants, sustainable management of floodplains or explain the fate of environmentally harmful substances.Our experiments in small groundwater lysimeter and biogeochemical microcosms tended to yield similar results regarding the functional relationships among the investigated site parameters. But the results of the field experiments, carried out at a floodplain site of the middle course of the Elbe River, Germany, are often characterized by complex and varying factors. Whereas arsenic tended to be mobilized during flooding due to decreasing redox potential (E_H), chromium showed the opposite trend, with peak concentrations at the highest E_H values. Our approach at three different spatiotemporally scale levels, ranging from 23 days (microcosms) to two-and-a-half years (field soil hydrological facility) allows us to overcome process interferences observed in field studies.     

Distances of dispersal of juvenile bivalves (Mya arenaria (Linnaeus), Mercenaria mercenaria (Linnaeus), Gemma gemma (Totten))

Although it is recognized that many species of benthic invertebrates continue to disperse after settlement, particularly in soft-bottom habitats, the scale over which movements of juveniles occur is not well known. This study combined laboratory flume experiments assessing the effects of clam size, species, and water velocity on rates and distances of dispersal of three species of juvenile bivalves with field measurements of loss rates and distances of dispersal of transplanted bivalves in the Navesink River estuary in New Jersey, USA. Dispersal distances measured in the laboratory ranged from an average of 1.6 to 40 cm h^− 1 depending on clam size, species, and flow speed. Distances and likelihood of dispersal were generally greater for Mya arenaria than for Mercenaria mercenaria or Gemma gemma, although differences between species were not consistent. As predicted, smaller (1.3 mm) M. arenaria tended to disperse more than larger (3.7 mm) ones, although no significant differences were detected between two sizes (1.8 and 3.4 mm) of M. mercenaria. The similarity of the erosion thresholds of dead clams across sizes and species suggests that burrowing behaviour plays an important role in determining variation in dispersal due to clam size and species. In the field, densities of clams (M.arenaria and M.mercenaria) were reduced to half of that in controls after 3.5-5 h, indicating high levels of dispersal and/or mortality. Some individuals were recovered up to 50 cm away from their initial locations. Overall, our results suggest that dispersal distances of these three species due to bedload transport are likely to be on the order of centimeters per hour. Although these dispersal distances are small, such movements are likely to occur frequently due to tidal currents and, consequently, may have profound impacts on patterns of abundance and distribution.