Growth responses of Zostera capricorni to estuarine sediment conditions

This study comprised (1) a field survey of intertidal seagrass (Zostera capricorni) biomass, cover and photosynthetic potential and sediment characteristics at a range of contrasting sites in three New Zealand harbours, and (2) a microcosm experiment comparing plant responses to sediments from extant versus historical seagrass sites. The field survey showed that the sediment physico-chemical characteristics were generally consistent with the limited previous reports for Zostera environments, although the total P concentration range was higher (0.08–0.72 mg P g⁻¹). Overall, 52% of variation in seagrass cover was explained by sediment water content (R = 0.54) and organic content (R = −0.56). Twenty-two percent of variation in seagrass biomass was explained by sediment total P and redox potential (both R = −0.35). Intra-harbour seagrass–sediment relationships were more significant (explaining up to 82% of plant variation) but harbour-specific. In the microcosm experiment, threefold higher Z. capricorni biomass was maintained on extant than historical sediments but not conclusively linked to measure sediment characteristics. Overall, the results of this study demonstrate that significant relations can exist between estuarine sediment conditions and Z. capricorni growth responses, and suggest that detrimental change in sediment conditions may be a contributing factor in seagrass decline.     

Growth responses of Zostera capricorni to estuarine sediment conditions

This study comprised (1) a field survey of intertidal seagrass (Zostera capricorni) biomass, cover and photosynthetic potential and sediment characteristics at a range of contrasting sites in three New Zealand harbours, and (2) a microcosm experiment comparing plant responses to sediments from extant versus historical seagrass sites. The field survey showed that the sediment physico-chemical characteristics were generally consistent with the limited previous reports for Zostera environments, although the total P concentration range was higher (0.08–0.72 mg P g⁻¹). Overall, 52% of variation in seagrass cover was explained by sediment water content (R = 0.54) and organic content (R = −0.56). Twenty-two percent of variation in seagrass biomass was explained by sediment total P and redox potential (both R = −0.35). Intra-harbour seagrass–sediment relationships were more significant (explaining up to 82% of plant variation) but harbour-specific. In the microcosm experiment, threefold higher Z. capricorni biomass was maintained on extant than historical sediments but not conclusively linked to measure sediment characteristics. Overall, the results of this study demonstrate that significant relations can exist between estuarine sediment conditions and Z. capricorni growth responses, and suggest that detrimental change in sediment conditions may be a contributing factor in seagrass decline.     

Thresholds for morphological response to light reduction for four tropical seagrass species

Seagrasses worldwide are highly vulnerable to, and at increasing risk from reduced light availability, and robust light thresholds are required for evaluating future impacts of changing light conditions. We tested the morphological response (shoot density and growth) of four Indo-West Pacific seagrass species (Cymodocea serrulata, Halodule uninervis, Halophila ovalis and Zostera muelleri) to six daily light levels ranging from 0 to 23 mol m⁻² d⁻¹ (0–70% surface irradiance) in cool (∼23 °C) and warm temperatures (∼28 °C) over 14 weeks. The impact of light limitation on shoot densities and growth rates was higher at warm than at cool temperatures, and for Z. muelleri and H. ovalis than for C. serrulata and H. uninervis, in terms of both the time taken for the low light treatment to take effect and the predicted time to shoot loss (e.g. 17–143 days at 0 mol m⁻² d⁻¹). Using fitted curves we estimated temperature-dependent thresholds (with estimates of uncertainty) for 50% and 80% protection of growth and shoot density, defined here as “potential light thresholds” in recognition that they were derived under experimental conditions. Potential light thresholds that maintained 50% and 80% of seagrass shoot density fell within the ranges 1.1–5.7 mol m⁻² d⁻¹ and 3.8–10.4 mol m⁻² d⁻¹, respectively, depending on temperature and species. Light thresholds calculated in separate in situ studies for two of the same species produced comparable results. We propose that the upper (rounded) values of 6 mol m⁻² d⁻¹ and 10 mol m⁻² d⁻¹ can be used as potential light thresholds for protecting 50% and 80% of shoot density for these four species over 14 weeks. As management guidelines should always be more conservative than thresholds for biological declines, we used error estimates to provide a quantitative method for converting potential light thresholds into guidelines that satisfy this criterion. The present study demonstrates a new approach to deriving potential light thresholds for acute impacts, describes how they can be applied in management guidelines and quantifies the timescales of seagrass decline in response to light limitation. This method can be used to further quantify cumulative impacts on potential light thresholds.     

Extent estimates and land cover relationships for functional indicators in non-wadeable rivers

Functional indicators are being increasingly used to assess waterway health but their responses to pressure in non-wadeable rivers have not been widely documented or applied in modern survey designs that provide unbiased estimates of extent. This study tests the response of river metabolism and loss in cotton strip tensile strength across a land use pressure gradient in non-wadeable rivers of northern New Zealand, and reports extent estimates for river metabolism and decomposition rates. Following adjustment for probability of selection, ecosystem respiration (ER) and gross primary production (GPP) for the target population of order 5–7 non-wadeable rivers averaged −7.3 and 4.8 g O₂ m⁻² d⁻¹, respectively, with average P/R < 1 indicating dominance by heterotrophic processes. Ecosystem respiration was <−3.3 g O₂ m⁻² d⁻¹ for 75% of non-wadeable river length with around 20% of length between −10 and −20 g O₂ m⁻² d⁻¹. Cumulative distribution functions of cotton strength loss estimates indicated a more-or-less linear relationship with river km reflecting an even spread of decay rates (range in k 0.0007–0.2875 d⁻¹) across non-wadeable rivers regionally. A non-linear relationship with land cover was detected for GPP which was typically <5 g O₂ m⁻² d⁻¹ where natural vegetation cover was below 20% and greater than 80% of upstream catchment area. For cotton strength loss, the relationship with land cover was wedge-shaped such that sites with >60% natural cover had low decay rates (<0.02 d⁻¹) with variability below this increasing as natural cover declined. Using published criteria for assessing waterway health based on ER and GPP, 232–298 km (20–29%) of non-wadeable river length was considered to have severely impaired ecosystem functioning, and 436–530 km (42–50%) had no evidence of impact on river metabolism.     

Comparison of Zostera marina and maerl community metabolism

The photosynthetic and repiratory metabolism of Zostera marina and maerl communities was compared, in the same area of the Bay of Brest in March–April, using benthic chambers. P–E curves for both oxygen and carbon were established for bottom irradiances between 0 and 525 μmol m⁻² s⁻¹. An exponential function was fitted to calculate daily production. Community metabolic quotients did not differ for maerl and seagrass beds. Community photosynthetic quotients were significantly higher (1.19) whereas community respiratory quotients were lower (0.70) than 1. Maerl and seagrass bed P–E curves mainly differed by the minimum saturating irradiance (E_k). Net community production was estimated to 26.8 mmol C m⁻² d⁻¹ for Z. marina meadows and 8.6 mmol C m⁻² d⁻¹ for maerl beds. The two communities can, therefore, be considered as autotrophic during the March–April period. Community respiration did not differ between Z. marina meadows and maerl beds, with an average value of 53.8 mmol C m⁻² d⁻¹ during a day. In similar environmental conditions, the production of maerl beds corresponds to approximately one third that of seagrass meadows. The maerl communities, therefore, form productive ecosystems, relevant to temperate coastal ecosystems functioning.     

Investigation on the properties and kinetics of glucose-fed aerobic granular sludge

Aerobic granulation is a process in which suspended biomass aggregate and form discrete well-defined granules in aerobic systems. To investigate the properties and kinetics of aerobic granular sludge, aerobic granules were cultivated with glucose synthetic wastewater in a series of sequencing batch reactors (SBR). The spherical shaped granules were observed on 8th day with the mean diameter of 0.1 mm. With the organic loading rate (OLR) being increased to 4.0 g COD L⁻¹ d⁻¹, aerobic granules grew matured with spherical shape. The size of granules ranged from 1.2 to 1.8 mm, and the corresponding settling velocity of individual granule was 24.2–36.4 m h⁻¹. The oxygen utilization rate (OUR) of mature granules was 41.90 g O₂ kg MLSS⁻¹ h⁻¹, which was two times higher than that of activated sludge (18.32 g O₂ kg MLSS⁻¹ h⁻¹). The experimental data indicated that the substrate utilization and biomass growth kinetics generally followed Monod's kinetics model. The corresponding kinetic coefficients of k (maximum specific substrate utilization rate), K_s (half velocity coefficient), Y (growth yield coefficient) and K_d (decay coefficient) were determined as follows, k_c = 23.65 d⁻¹, K_c = 3367.05 mg L⁻¹, K_N = 0.038 d⁻¹, K_N = 29.65 mg L⁻¹, Y = 0.1927–0.2022 mg MMLS (mg COD)⁻¹ and K_d = 0.00845–0.0135 d⁻¹, respectively. Those properties of aerobic granules made aerobic granules system had a short setup period, high substrate utilization rate and low sludge production.     

Fire service instructor's undergarment choice to reduce Interleukin-6 and minimise physiological and perceptual strain

Fire Service Instructors frequently experience high levels of physiological and perceptual strain during live fire exposures. Instructors are also at risk of cardiovascular illnesses, with cardiac death being the greatest cause of fire fighter death. Current practice for UK instructors is to select undergarment type based on personal preference, between a boiler suit (BOILER) and a wicking base layer (WBL). Research suggests that shorts and t-shirt (SHORTS) may also be a beneficial alternative undergarment choice. The UK South East Fire Service requested an investigation to identify if undergarment selection can lessen the strain experienced by instructors, and reduce the acute inflammatory response to fire exposures. Eight males completed three 45 min sessions in a heat chamber (49.5±1.4 °C and 16.9±4.3% RH) whilst performing intermittent walking. At the end of heat exposure change in heart rate was not effected by garment type (p=0.061, ηp²=0.373). Change in rectal temperature was different between garments (p=0.009, η_p²=0.271), with trends suggesting that BOILER resulted in a greater change (1.03±0.60 °C) than SHORTS (0.76±0.37 °C, p=0.589, d=0.21) and WBL (0.72±0.33 °C, p=0.545, d=0.25). Interleukin-6 post exposure was greater for BOILER (6.96±0.28 pg mL⁻¹) than both SHORTS (6.59±0.30 pg mL⁻¹, p=0.043, d=0.42) and WBL (6.45±0.43 pg mL⁻¹, p=0.031, d=0.51). Overall, undergarment type had little impact on physiological or perceptual strain. However, wearing WBL or SHORTS may reduce the inflammatory response, and consequently decrease the risk of cardiovascular events.     

Improved retrieval of Secchi depth for optically-complex waters using remote sensing data

Water transparency is one of the ecological indicators for describing water quality and the underwater light field which determines its productivity. In the European Water Framework Directive (WFD) as well as in the European Marine Strategy Framework Directive (MSFD) water transparency is used for ecological status classification of inland, coastal and open sea waters and it is regarded as an indicator for eutrophication in Baltic Sea management (HELCOM, 2007). We developed and compared different empirical and semi-analytical algorithms for lakes and coastal Nordic waters to retrieve Secchi depth (Z_SD) from remote sensing data (MERIS, 300 m resolution). The algorithms were developed in water bodies with high coloured dissolved organic matter absorption (a_CDOM(442) ranging 1.7–4.0 m⁻¹), Chl a concentration (0.5–73 mg m⁻³) and total suspended matter (0.7–37.5 g m⁻³) and validated against an independent data set over inland and coastal waters (0.6 m < Z_SD < 14.8 m). The results indicate that for empirical algorithms, using longer wavelengths in the visible spectrum as a reference band decreases the RMSE and increases the coefficient of determination (R²). The accuracy increased (R² = 0.75, RMSE = 1.33 m, n = 134) when Z_SD was retrieved via an empirical relationship between Z_SD and K_d(490). The best agreement with in situ data was attained when Z_SD was calculated via both the diffuse and the beam attenuation coefficient (R² = 0.89, RMSE = 0.77 m, n = 89). The results demonstrate that transparency can be retrieved with high accuracy over various optical water types by the means of ocean color remote sensing, improving both the spatial and temporal coverage. The satellite derived Z_SD product could be therefore used as an additional source of information for WFD and MSFD reporting purposes.     

The effects of light intensity on the growth of Japanese Gambierdiscus spp. (Dinophyceae)

Marine toxic dinoflagellates of the genus Gambierdiscus are the causative agents of ciguatera fish poisoning (CFP), a form of seafood poisoning that is widespread in tropical, subtropical and temperate regions worldwide. The distributions of Gambierdiscus australes, Gambierdiscus scabrosus and two phylotypes of Gambierdiscus spp. type 2 and type 3 have been reported for the waters surrounding the main island of Japan. To explore the bloom dynamics and the vertical distribution of these Japanese species and phylotypes of Gambierdiscus, the effects of light intensity on their growth were tested, using a photoirradiation-culture system. The relationship between the observed growth rates and light intensity conditions for the four species/phylotypes were formulated at R > 0.92 (p < 0.01) using regression analysis and photosynthesis-light intensity (P-L) model. Based on this equation, the optimum light intensity (L_max) and the semi-optimum light intensity range (L_s-opt) that resulted in the maximum growth rate (μ_max) and ≥80% μ _max values of the four species/phylotypes, respectively, were as follows: (1) the L_max and L_s-opt of G. australes were 208 μmol photons m⁻² s⁻¹ and 91–422 μmol photons m⁻² s⁻¹, respectively; (2) those of G. scabrosus were 252 and 120–421 μmol photons m⁻² s⁻¹, respectively; (3) those of Gambierdiscus sp. type 2 were 192 and 75–430 μmol photons m⁻² s⁻¹, respectively; and (4) those of Gambierdiscus sp. type 3 were ≥427 and 73–427 μmol photons m⁻² s⁻¹, respectively. All four Gambierdiscus species/phylotypes required approximately 10 μmol photons m⁻² s⁻¹ to maintain growth. The light intensities in coastal waters at a site in Tosa Bay were measured vertically at 1 m intervals once per season. The relationships between the observed light intensity and depth were formulated using Beer’s Law. Based on these equations, the range of the attenuation coefficients at Tosa Bay site was determined to be 0.058–0.119 m⁻¹. The values 1700 μmol photons m⁻² s⁻¹, 500 μmol photons m⁻² s⁻¹, and 200 μmol photons m⁻² s⁻¹ were substituted into the equations to estimate the vertical profiles of light intensity at sunny midday, cloudy midday and rainy midday, respectively. Based on the regression equations coupled with the empirically determined attenuation coefficients for each of the four seasons, the ranges of the projected depths of L_max and L_s-opt for the four Gambierdiscus species/phylotypes under sunny midday conditions, cloudy midday conditions, and rainy midday conditions were 12–38 m and 12–54 m, 1–16 m and 1–33 m, and 0 m and 0–16 m, respectively. These results suggest that light intensity plays an important role in the bloom dynamics and vertical distribution of Gambierdiscus species/phylotypes in Japanese coastal waters.     

Evaluation of the effects of light intensity on growth of the benthic dinoflagellate Ostreopsis sp. 1 using a newly developed photoirradiation-culture system and a novel regression analytical method

Benthic dinoflagellates of the genus Ostreopsis are found all over the world in temperate, subtropical, and tropical coastal regions. Our recent studies revealed that a putative “cryptic” species of Ostreopsis ovata is present widely along Japanese coasts. This organism, Ostreopsis sp. 1, possesses palytoxin analogs and thus its toxic blooms may be responsible for potential toxification of marine organisms. To evaluate the bloom dynamics of Ostreopsis sp. 1, the present study examined the growth responses of Ostreopsis sp. 1 strain s0716 to various light intensities (photon flux densities: μmol photons m⁻² s⁻¹) using a newly devised photoirradiation-culture system. This novel system has white light-emitting diodes (LEDs) capable of more closely simulating the wavelength spectrum of light entering the oceanic water column than do fluorescent tubes and halogen lamps. In this system, the light intensity of the white LEDs was reduced through two polarizing filters by varying the rotation angles of the filters. Thereby, the new system was capable of culturing microalgae under well-controlled light intensity conditions. Ostreopsis sp. 1 grew proportionally when light intensity was increased from 49.5 to 199 μmol photons m⁻² s⁻¹, but its growth appeared to be inhibited slightly at ≥263 μmol photons m⁻² s⁻¹. The relationship between observed growth rates and light intensity was calculated at R > 0.99 (P < 0.01) using a regression analysis with a modified equation of the photosynthesis-light intensity (P-L) model. The equation determined the critical light intensities for growth of Ostreopsis sp. 1 and the organism's growth potential as follows: (1) the threshold light intensity for growth: 29.8 μmol photons m⁻² s⁻¹; (2) the optimum light intensity (L_m) giving the maximum growth rate (μ_max = 0.659 divisions day⁻¹): 196 μmol photons m⁻² s⁻¹; (3) the optimum light intensity range (L_opt) giving ≥95% μ_max: 130–330 μmol photons m⁻² s⁻¹; (4) the semi-optimum range (L_sopt) giving ≥80% μ_max: 90 to over 460 μmol photons m⁻² s⁻¹. The L_sopt represents 4.5–23% ambient light intensity present in surface waters off of a temperate region of the Japanese coast, Tosa Bay; putatively, this semi-optimum range of light intensity appears at depth of 12.9–27.8 m. Considering these issues, our data indicate that Ostreopsis sp. 1 in coastal environments may form blooms at ca. ∼28 m depth in regions along Japanese coasts.     

The effects of NH4+ and NO3− on growth,resource allocation and nitrogen uptake kinetics of Phragmites australis and Glyceria maxima

The effects of NH₄⁺ or NO₃⁻ on growth, resource allocation and nitrogen (N) uptake kinetics of two common helophytes Phragmites australis (Cav.) Trin. ex Steudel and Glyceria maxima (Hartm.) Holmb. were studied in semi steady-state hydroponic cultures. At a steady-state nitrogen availability of 34 μM the growth rate of Phragmites was not affected by the N form (mean RGR = 35.4 mg g⁻¹ d⁻¹), whereas the growth rate of Glyceria was 16% higher in NH₄⁺-N cultures than in NO₃⁻-N cultures (mean = 66.7 and 57.4 mg g⁻¹ d⁻¹ of NH₄⁺ and NO₃⁻ treated plants, respectively). Phragmites and Glyceria had higher S/R ratio in NH₄⁺ cultures than in NO₃⁻ cultures, 123.5 and 129.7%, respectively.Species differed in the nitrogen utilisation. In Glyceria, the relative tissue N content was higher than in Phragmites and was increased in NH₄⁺ treated plants by 16%. The tissue NH₄⁺ concentration (mean = 1.6 μmol g fresh wt⁻¹) was not affected by N treatment, whereas NO₃⁻ contents were higher in NO₃⁻ (mean = 1.5 μmol g fresh wt⁻¹) than in NH₄⁺ (mean = 0.4 μmol g fresh wt⁻¹) treated plants. In Phragmites, NH₄⁺ (mean = 1.6 μmol g fresh wt⁻¹) and NO₃⁻ (mean = 0.2 μmol g fresh wt⁻¹) contents were not affected by the N regime. Species did not differ in NH₄⁺ (mean = 56.5 μmol g⁻¹ root dry wt h⁻¹) and NO₃⁻ (mean = 34.5 μmol g⁻¹ root dry wt h⁻¹) maximum uptake rates (V_max), and V_max for NH₄⁺ uptake was not affected by N treatment. The uptake rate of NO₃⁻ was low in NH₄⁺ treated plants, and an induction phase for NO₃⁻ was observed in NH₄⁺ treated Phragmites but not in Glyceria. Phragmites had low K_m (mean = 4.5 μM) and high affinity (10.3 l g⁻¹ root dry wt h⁻¹) for both ions compared to Glyceria (K_m = 6.3 μM, affinity = 8.0 l g⁻¹ root dry wt h⁻¹). The results showed different plasticity of Phragmites and Glyceria toward N source. The positive response to NH₄⁺-N source may participates in the observed success of Glyceria at NH₄⁺ rich sites, although other factors have to be considered. Higher plasticity of Phragmites toward low nutrient availability may favour this species at oligotrophic sites.     

Factors controlling Zostera marina L. growth in the eastern and western Pacific Ocean: Comparisons between Korea and Oregon,USA

Zostera marina distribution is circum-global and tolerates a wide range of environmental conditions. Consequently, it is likely that populations have adapted to local environmental conditions of light, temperature and nutrient supply. We compared Z. marina growth dynamics over a 2-year period in relation to environmental characters at Jindong Bay, South Korea and Yaquina Bay, Oregon, USA. Water temperature in Jindong Bay showed stronger seasonal variation (summer–winter ΔT = 20 °C) than in Yaquina Bay (summer–winter ΔT < 5 °C). Underwater irradiance in Jindong Bay exhibited a winter maximum, while in Yaquina Bay underwater light exhibited a summer maximum. Integrated annual underwater irradiance during 2003 was 2200 and 1200 mol photons m⁻² year⁻¹ in Korea and Oregon, respectively. Z. marina shoot density, biomass and integrated production were not significantly different between the two study sites. Seasonal Z. marina growth in Jindong Bay appeared to be controlled by temperature and light, while the growth pattern in Yaquina Bay suggested light regulation. Several seagrass parameters were correlated to phosphate concentrations, even though nutrients did not appear limiting. Despite differences in environmental factors, relative growth rates and temporal growth dynamics between study sites, integrated annual leaf production was quite similar at 335 and 353 g DW m⁻² year⁻¹ in the Jindong and Yaquina Bay study sites. We suggest that Z. marina net productivity is acclimated to the local environmental conditions and may be a general characteristic of temperate seagrass populations.     

Seasonal variations in photosynthetic irradiance response curves of macrophytes from a Mediterranean coastal lagoon

The main photosynthesis and respiration parameters (dark respiration rate, light saturated production rate, saturation irradiance, photosynthetic efficiency) were measured on a total of 23 macrophytes of the Thau lagoon (2 Phanerogams, 5 Chlorophyceae, 10 Rhodophyceae and 6 Phaeophyceae). Those measurements were performed in vitro under controlled conditions, close to the natural ones, and at several seasons. Concomitantly, measurements of pigment concentrations, carbon, phosphorous and nitrogen contents in tissues were performed. Seasonal intra-specific variability of photosynthetic parameters was found very high, enlightening an important acclimatation capacity. The highest photosynthetic capacities were found for Chlorophyceae (e.g. Monostroma obscurum thalli at 17 °C, 982 μmol O₂ g⁻¹ dw h⁻¹ and 9.1 μmol O₂ g⁻¹ dw h⁻¹/μmol photons m⁻² s⁻¹, respectively for light saturated net production rate and photosynthetic efficiency) and Phanerogams (e.g. Nanozostera noltii leaves at 25 °C, 583 μmol O₂ g⁻¹ dw h⁻¹ and 2.6 μmol O₂ g⁻¹ dw h⁻¹/μmol photons m⁻² s⁻¹ respectively for light saturated net production rate and photosynthetic efficiency). As expected, species with a high surface/volume ratio were found to be more productive than coarsely branched thalli and thick blades shaped species. Contrary to R_d (ranging 6.7–794 μmol O₂ g⁻¹ dw h⁻¹, respectively for Rytiphlaea tinctoria at 7 °C and for Dasya sessilis at 25 °C) for which a positive relationship with water temperature was found whatever the species studied, the evolution of P/I curves with temperature exhibited different responses amongst the species. The results allowed to show summer nitrogen limitation for some species (Gracilaria bursa-pastoris and Ulva spp.) and to propose temperature preferences based on the photosynthetic parameters for some others (N. noltii, Zostera marina, Chaetomorpha linum).     

Environmental determinants of Gulf Menhaden (Brevoortia patronus) oil content in the northern Gulf of Mexico

Gulf Menhaden (Brevoortia patronus) are a species of commercial and ecological importance in the northern Gulf of Mexico, provisioning the second largest fishery by weight, in the United States, and providing critical ecosystem services in the coastal region. The recruitment and productivity dynamics of the stock are influenced by a suite of environmental factors but an understanding of the factors that determine individual variation in oil content (an indicator of an individual’s commercial value to the fishery and its dietary value to predators) has not been well described. In this work I describe the temporal dynamics of oil content and determine the demographic characteristics that provide predictive power to describe annual contrasts. I relate the predicted patterns in oil yield to a suite of seasonal environmental data series including: the magnitude of spring Mississippi River discharge, spring wind vectors, and the preceding winter El Nino conditions. Two uncorrelated (r = 0.06, p = 0.81) population-level predictor variables were identified that have explanatory power to describe temporal patterns in oil content (L kg⁻¹); a weight-at-length power function parameter (a) and the von Bertalanffy asymptotic fork length (L_∞, mm FL): L kg⁻¹ = − 0.158 − 0.026*a − 0.00163*L_∞ (p < 0.05, R² = 0.42). Analysis of the impacts of environmental variables on the oil content of Gulf Menhaden was evaluated comprehensively in a Bayesian framework by transforming the observed oil content information from two sources to a common scale. Parameters relating oil content to spring Mississippi River discharge and the preceding winter (December–February) El Nino Southern Oscillation index resulted in sample distributions from the posterior where zero was outside the 95% credible interval. This work contributes to the understanding of Gulf Menhaden as a prey species in the Gulf of Mexico and indicates that the value of the species to both the fishery and predators exhibits relatively large inter-annual variability controlled, in part, by seasonal environmental conditions.     

Flow velocity affects internal oxygen conditions in the seagrass Cymodocea nodosa

The internal oxygen status of seagrass tissues, which is believed to play an important role in events of seagrass die-off, is partly determined by the rates of gas exchange between leaves and water column. In this study, we examined whether water column flow velocity has an effect on gas exchange, and hence on internal oxygen partial pressures (pO₂) in the Mediterranean seagrass, Cymodocea nodosa. We measured the internal pO₂ in the horizontal rhizomes of C. nodosa in darkness at different mainstream flow velocities, combined with different levels of water column oxygen pO₂ using an experimental flume in the laboratory. Flow velocity clearly had an effect on the internal oxygen status. In stagnant, but fully aerated water the mean internal pO₂ was 6.9 kPa, corresponding to about 30% of air saturation. The internal pO₂ increased with increasing flow velocity reaching saturation of around 12.2 kPa (60% of air saturation) at flow velocities ≥7 cm s⁻¹. Flow had a relatively larger influence on internal pO₂ at lower water column oxygen concentrations. By extrapolating linear relationships between internal and water column pO₂ in this experimental setup, rhizomes would become anoxic at a water column oxygen pO₂ of 4–4.5 kPa (∼20% of air saturation) in flowing water, but already at 6.4 kPa (∼30% of air saturation) in stagnant water. Water flow may play an important role for seagrass performance and survival in areas with poor water column oxygen conditions and may, in general, be of importance for the distribution of submerged rooted plants.     

Trispyrazolylmethane piano stool complexes of iron(II) and cobalt(II)

A series of cationic trispyrazolylmethane complexes of the general form [Tm^RM(CH₃CN)₃]²⁺ (Tm = tris(pyrazolyl)methane, 1, R = 3,5-Me₂, M = Fe(II); 2, R = 3-Ph, M = Fe(II); 3, R = 3,5-Me₂, M = Co(II); 4, R = 3-Ph, M = Co(II)) with ‘piano-stool’ structures was prepared by the reaction of the N₃tripodal ligands (Tm^R)with [(CH₃CN)₆M](BF₄)₂ in a 1:1 stoichiometric ratio. Magnetic susceptibility measurements indicate that all four complexes with BF₄⁻ counter anions are paramagnetic, high-spin systems in the solid state with μ_eff at high temperatures of 5.2 (1, S = 2), 5.4 (2, S = 2), 4.9 (3, S = 3/2) and 4.6 (4, S = 3/2) BM, respectively. Comparisons of bond lengths from the metal centre to the Tm^R nitrogen donors, and from the metal centre to the acetonitrile nitrogen donors indicate that the neutral tripodal ligands appear to be more weakly coordinated to the metal centre than are the acetonitrile ligands. Reactions of these tripodal complexes with bidentate phosphine ligands, such as 1,2-diphosphinoethane or 1,2-bis(diallylphosphino)ethane leads to displacement of the tripodal ligand, or to the formation of more thermally stable bis-ligand complexes M(Tm^R)₂ (R = 3,5-dimethyl).     

Kinetics of biodegradation of free gossypol by Candida tropicalis in solid-state fermentation

In the present work experiments were carried out to study the effect of free gossypol on the growth of Candida tropicalis ZAU-1, evaluate its ability in biodegrading free gossypol, analyze the time course of solid-state fermentation, and model the microbial growth by determining the kinetics of dry matter weight loss, total carbohydrate concentration and the free gossypol content during solid-state fermentation. Results showed that the biomass in inorganic salts glucose medium were unaffected by free gossypol at 500 and 1000 mg/l levels, compared with the control group (p > 0.05); degradation of free gossypol reached 95.12% and 94.12%, respectively. A logistic equation (R² = 0.9922), describing the growth model of C. tropicalis ZAU-1 was obtained, with the maximum values of u_m and X_m at 0.0970 h⁻¹ and 21.8631% of dry matter weight loss, respectively. A good-fit curvilinear regression model was achieved to describe the change pattern of total carbohydrate concentration (R² = 0.9910), and the biodegradation pattern of free gossypol (R² = 0.9825). These models could be used to predict the fermentation course by C. tropicalis ZAU-1 under solid-state fermentation.     

Diurnal exchanges of CO2 and CH4 across the water–atmosphere interface in a water chestnut meadow (Trapa natans L.)

CH₄ and CO₂ fluxes across the water–atmosphere interface were measured over a 24 h day–night cycle in a shallow oxbow lake colonized by the water chestnut (Trapa natans L.) (Lanca di Po, Northern Italy). Only exchanges mediated by macrophytes were measured, whilst gas ebullition was not considered in this study. Measurements were performed from 29 to 30 July 2005 with short incubations, when T. natans stands covered the whole basin surface with a mean dry biomass of 504 ± 91 g m⁻². Overall, the oxbow lake resulted net heterotrophic with plant and microbial respiration largely exceeding carbon fixation by photosynthesis. The water chestnut stand was a net sink of CO₂ during the day-light period (−60.5 ± 8.5 mmol m⁻² d⁻¹) but it was a net source at night (207.6 ± 6.1 mmol m⁻² d⁻¹), when the greatest CO₂ efflux rate was measured across the water surface (28.2 ± 2.4 mmol m⁻² h⁻¹). The highest CH₄ effluxes (6.6 ± 1.8 mmol m⁻² h⁻¹) were determined in the T. natans stand during day-time, whilst CH₄ emissions across the plant-free water surface were greatest at night (6.8 ± 2.1 mmol m⁻² h⁻¹). Therefore, we assumed that the water chestnut enhanced methane delivery to the atmosphere. On a daily basis, the oxbow lake was a net source to the atmosphere of both CO₂ (147.1 ± 10.8 mmol m⁻² d⁻¹) and CH₄ (116.3 ± 8.0 mmol m⁻² d⁻¹).     

Investigation on the formation and kinetics of glucose-fed aerobic granular sludge

Aerobic granular sludge was cultivated in a glass sequencing batch reactor (SBR) with glucose synthetic wastewater. The spherical shaped granules were observed on 4th day with the mean diameter of 0.1 mm. With the increase of chemical oxygen demand (COD) concentration of the influent, aerobic granules grew matured, the size of which ranged from 1.2 to 1.9 mm. The aerobic granular sludge could sustain high organic loading rate (about 4.0 g COD L⁻¹ d⁻¹), with good settling ability (settling velocity 36 m/h) and high biomass concentration (MLSS 6.7 ±0.2 g/L). Experimental data indicated that the substrate utilization and biomass growth kinetics followed Monod's kinetics model approximately. The corresponding kinetic coefficients of maximum specific substrate utilization rate (k), half velocity coefficient (K_s), growth yield coefficient (Y) and decay coefficient (K_d) were 13.2 d⁻¹, 275.8 mg/L, 0.183–0.250 mg MLSS/mg COD and 0.023–0.075 d⁻¹, respectively, which made aerobic granules have short setup period, high rate of substrate utilization and little surplus sludge.     

Patch dynamics of the Mediterranean seagrass Posidonia oceanica: Implications for recolonisation process

Patch dynamics of the Mediterranean slow-growing seagrass Posidonia oceanica was studied in two shallow sites (3–10 m) of the Balearic Archipelago (Spain) through repeated censuses (1–2 year⁻¹). In the sheltered site of Es Port Bay (Cabrera Island), initial patch density (October 2001) was low: 0.05 patches m⁻², and the patch size (number of shoots) distribution was bimodal: most of the patches had less than 6 shoots or between 20 and 50 shoots. Mean patch recruitment in Es Port Bay (0.006 ± 0.002 patches m⁻² year⁻¹) exceeded mean patch loss (0.001 ± 0.001 patches m⁻² year⁻¹), yielding positive net patch recruitment (0.004 ± 0.003 patches m⁻² year⁻¹) and a slightly increased patch density 3 years later (July 2004, 0.06 patches m⁻²). In the exposed site of S’Estanyol, the initial patch density was higher (1.38 patches m⁻², August 2003), and patch size frequency decreased exponentially with size. Patch recruitment (0.26 patches m⁻² year⁻¹) and loss (0.24 patches m⁻² year⁻¹) were high, yielding a slightly increased patch density in the area 1 year later (October 2004, 1.40 patches m⁻²). Most recruited patches consisted of rooting vegetative fragments of 1–2 shoots. Seedling recruitment was observed in Summer 2004 at both sites. Episodic, seedling recruitment comprised 30% and 25% of total patch recruitment in Es Port Bay and S’Estanyol, respectively. Patch survival increased with patch size and no direct removal was observed among patches of 5 shoots or more. Most patches grew along the study, shifting patch distribution towards larger sizes. Within the size range studied (1–150 shoots), absolute shoot recruitment (shoots year⁻¹) increased linearly with patch size (R² = 0.64, p < 4 × 10⁻⁵, N = 125), while specific shoot recruitment was constant (about 0.25 ± 0.05 year⁻¹), although its variance was large for small patches. Given the slow growth rate and the high survival of patches with 5 or more shoots, even the low patch recruitment rates reported here could play a significant role in the colonisation process of P. oceanica.