A model of chlorophyll a destruction by Calanus spp. and implications for the estimation of ingestion rates using the gut fluorescence method

Chlorophyll a (chl a) destruction by groups of Calanus spp. with different long-term in situ feeding histories was compared. For copepods that had fed during both pre- and early-bloom conditions, degrees of chl a destruction were relatively constant at high ingestion rates and increased as ingestion rates decreased. Assuming that 2 pools of chlorophyll bleaching enzymes (CBEs) were involved in the destruction of chl a (one derived from the copepods and one from the ingested algae), a new model was developed to describe the kinetics of chl a destruction. In this model, the CBE activity of each pool was described using a Michaelis-Menten expression and the total CBE activity was given by the sum of the 2 expressions. Parameter estimates of V(c)(max), the maximum activity of the copepod CBE, were higher for the early-bloom copepods than for the pre-bloom copepods, suggesting that the former had a higher destructive capacity. Estimates of R(p)(max), the phytoplankton 'CBE activity coefficient' which is analogous to V(max), were similar between the 2 groups of experiments. This is reasonable since most of the food fed to the copepods was healthy, actively growing diatoms. The model could also describe the kinetics of chl a destruction for Calanus spp. that had fed during late-bloom conditions. For the late-bloom data, V(c)(max) and R(p)(max) values were higher than for the pre- and early-bloom copepods and phytoplankton. This suggests that the late-bloom copepods and the in situ phytoplankton that they ate had higher destructive capacities, perhaps because the spring-bloom was more advanced. Expressions were derived from the new model to describe the relationship between real ingestion rate (I(r)) and apparent ingestion rate (I(a)), over a range of I(a) values, where the latter are values which would have been determined using gut fluorescence methodology. Correction factors (I(r)/I(a)) varied by a factor of less than 2 (for I(a) values ranging from 0.1 to 100 ng chi a ind.-1 h-1) between different groups of copepods (pre-, early- and late-bloom) and sources of algae (actively growing and senescent). In future it will be important to validate this model under controlled conditions (e.g. using single species of copepods and phytoplankton food) and to assess whether correction factors derived from our model are generally applicable, if results of studies using gut fluorescence methods are to be interpreted properly

Conference pears; work on system changes to enable better scab control in organic orchards in the Netherlands

Scab control in Conference pears is the bottleneck in organic growing. A group of growers, advisers and researchers in the Netherlands is working on new approaches to organic pear growing. Central to this approach is a reliable and good scab control. Changes in the system of cultivation are sought which will enable this scab control with less fungicide. This has become even more urgent since copper was banned as a fungicide in the Netherlands. First results from trials on vigour control show that there is potency for system changes that will enable a better scab control in organic growing. Scab incidence was reduced in three trials with 34, 58 and 82% respectively. The project, in which also other cultivation measures are being tested, will be continued

Brown Tide Symposium and Workshop : 15-16 July 1991

The 'brown tide' bloom of an aberrant Chrysophyte sp. phytoplankter occurred for more than 18 months and extended into both upper (cover map) and lower Laguna Madre, Texas. Great concern for the Laguna Madre ecosystem was shown during the brown tide event by local, state and regional groups, but little previous knowledge was available about this unusual phytoplankton bloom. Since field data had been collected by an ongoing UTMSI field program in the Laguna, it was felt that a workshop format meeting should be convened with national and international experts to discuss the data and results on brown tide and other unusual phytoplankton blooms. A relatively quick response was needed as planning for the workshop started in May 1991 for a meeting date in July, with support supplied by the Gulf of Mexico Program of U.S. Environmental Protection Agency (Grant No. X 006242-01-0), The Resource Protection Division of the Texas Parks and Wildlife Department and The University of Texas Marine Science Institute. This report includes the agenda, abstracts of presentations and summary of findings by the workshop participants. The participants also strongly agreed that long term research support was necessary to further understand the brown tide bloom and its effects. To that end, a resolution was drafted and unanimously approved by all the workshop participants.September 1991Marine Scienc

Are marine diatoms favoured by high Si:N ratios?

Competition experiments were performed first with 4, then with 11 species of marine phytoplankton at various ratios of si1icate:nitrate and various light intensities. Diatoms became dominant at Si:N ratios >25:1 while flagellates were the superior competitors at lower ratios. The light supply did not influence the competitive position of diatoms and non-siliceous flagellates in general, while it was important in determining the outcome of competition at the species level. In the 11 species expenments, Stephanopyxis palmenana was the dominant diatom at high light intensities. It shared dominance with Lauderia annulata at medium and low light intensities and high Si.N ratios. Pseudonitzschia pungens was the dominant diatom at low light intensities and relatively low Si:N ratios. The green alga Dunaliella tertiolecta was the dominant flagellate at high light intensities, while at low light intensities the prymnesiophycean Chrysochromulina polylepis and the cryptophyte Rhodomonas sp. were also important

Bottom mixed layer oxygen dynamics in the Celtic Sea

The seasonally stratified continental shelf seas are highly productive, economically important environments which are under considerable pressure from human activity. Global dissolved oxygen concentrations have shown rapid reductions in response to anthropogenic forcing since at least the middle of the twentieth century. Oxygen consumption is at the same time linked to the cycling of atmospheric carbon, with oxygen being a proxy for carbon remineralisation and the release of CO2. In the seasonally stratified seas the bottom mixed layer (BML) is partially isolated from the atmosphere and is thus controlled by interplay between oxygen consumption processes, vertical and horizontal advection. Oxygen consumption rates can be both spatially and temporally dynamic, but these dynamics are often missed with incubation based techniques. Here we adopt a Bayesian approach to determining total BML oxygen consumption rates from a high resolution oxygen time-series. This incorporates both our knowledge and our uncertainty of the various processes which control the oxygen inventory. Total BML rates integrate both processes in the water column and at the sediment interface. These observations span the stratified period of the Celtic Sea and across both sandy and muddy sediment types. We show how horizontal advection, tidal forcing and vertical mixing together control the bottom mixed layer oxygen concentrations at various times over the stratified period. Our muddy-sand site shows cyclic spring-neap mediated changes in oxygen consumption driven by the frequent resuspension or ventilation of the seabed. We see evidence for prolonged periods of increased vertical mixing which provide the ventilation necessary to support the high rates of consumption observed

Drivers and food web effects of Gonyostomum semen blooms

The flagellate Gonyostomum semen forms dense late-summer blooms in humic lakes and is a nuisance to swimmers because it forms a slimy coat on the skin, causing irritation in sensitive individuals. Increasing occurrence and bloom incidence of G. semen has been reported during recent decades, but it is not clear which factors affect the distribution and bloom formation of this alga. Large cell size, ejection of long, slimy threads (trichocysts), and nighttime migration to the hypolimnion may limit grazing on G. semen by herbivorous zooplankton, resulting in a decreased coupling between phytoplankton and higher trophic levels during blooms. The studies included in this thesis investigate which factors affect G. semen occurrence and bloom formation and how G. semen blooms affect the community composition and trophic interactions in boreal, humic lakes. The occurrence of G. semen has increased between 1995 and 2010, especially in southern Sweden. Bloom incidence and total biomass did not increase continually, but fluctuated among years and peaked in the middle of the study period. Temperature and length of the growing season affected the occurrence and, to a lesser extent, bloom formation of G. semen, but local factors such as pH and water colour were more important for bloom formation. More lakes may become suitable habitats with the ongoing increase in water colour and increasing temperatures may result in a more frequent occurrence and bloom formation of G. semen. Blooms resulted in a shift in zooplankton assemblages toward predominance by small cladocerans, which were not able to feed on G. semen but instead fed more on heterotrophic food resources, supporting the hypothesis of a reduced coupling between phytoplankton and zooplankton. Zooplankton assemblages predominated by small animals feeding on low-quality resources may reduce the food quality for planktivorous fish. Instead, the invertebrate predator C. flavicans appeared to benefit from G. semen blooms, as indicated by its high abundance in bloom-lakes. Calanoid copepods and a large cladoceran fed efficiently on G. semen in the laboratory, indicating that there is, however, some trophic coupling between G. semen and higher trophic levels. This supports the use of biomanipulation of fish communities for controlling G. semen blooms

Spraying Program and Pest Control for Fruit Crops

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Springtime dandelion (Taraxacum officinale) control with seven postemergence herbicides applied at three anthesis stages

Although spring is not considered the optimal time for herbicidal control of most cool-season broadleaf weeds in turfgrass, spring applications are often required. Most new postemergence broadleaf herbicides combine several active ingredients, possibly resulting in synergistic, antagonistic, or additive effects. Therefore, as new herbicides become available, information is needed about their performance when applied in the spring. The objective of our study was to determine the effect of spring application timing on dandelion control with seven commercially available postemergence herbicides. Products were applied at their lowest labeled rate for dandelion control at three spring application timings, which coincided with dandelion anthesis stages (pre-, peak-, or post-bloom). A grid was used to determine percent dandelion control at several rating dates. The 2010 site had a denser turfgrass stand with smaller dandelions and was irrigated more frequently compared with the 2011 site. In 2010, all herbicides gave 98% or greater control at 30 days after treatment (DAT) when applied post-bloom; when applied pre- or peak-bloom, control was 80% or greater for all herbicides except for two products applied peak-bloom. At pre- and peak-bloom, products combining a protoporphyrinogen oxidase (PPO) inhibitor with a 2,4-D ester formulation were superior to most other herbicides. When evaluated at the end of the growing season in 2010, all herbicides provided 89% or greater control at all three timings. In 2011, with a less dense turfgrass stand, larger dandelions, and less frequent irrigation, control was more variable and shorter-lived among herbicides. When applied pre-bloom, all products containing 2,4-D provided 87% or greater control 60 DAT. Post-bloom application generally gave similar control to the pre-bloom timing. Peak-bloom application resulted in the poorest overall control at 60 DAT, but products combining a PPO inhibitor with a 2,4-D ester formulation performed better than most other herbicides. By the end of the season, dandelion regrowth caused reduced overall control at all timings, but overall control was poorest when applied at peak-bloom. In summary, peak-bloom applications should be avoided, especially if dandelion pressure is high. Products combining PPO inhibitors with ester forms of 2,4-D were most effective across all spring application timings. Products containing amine forms of 2,4-D may provide effective control if applied pre- or post-bloom

Seasonal succession of free-living bacterial communities in coastal waters of the Western Antarctic Peninsula

© The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Frontiers in Microbiology 7 (2016): 1731, doi: 10.3389/fmicb.2016.01731.The marine ecosystem along the Western Antarctic Peninsula undergoes a dramatic seasonal transition every spring, from almost total darkness to almost continuous sunlight, resulting in a cascade of environmental changes, including phytoplankton blooms that support a highly productive food web. Despite having important implications for the movement of energy and materials through this ecosystem, little is known about how these changes impact bacterial succession in this region. Using 16S rRNA gene amplicon sequencing, we measured changes in free-living bacterial community composition and richness during a 9-month period that spanned winter to the end of summer. Chlorophyll a concentrations were relatively low until summer when a major phytoplankton bloom occurred, followed 3 weeks later by a high peak in bacterial production. Richness in bacterial communities varied between ~1,200 and 1,800 observed operational taxonomic units (OTUs) before the major phytoplankton bloom (out of ~43,000 sequences per sample). During peak bacterial production, OTU richness decreased to ~700 OTUs. The significant decrease in OTU richness only lasted a few weeks, after which time OTU richness increased again as bacterial production declined toward pre-bloom levels. OTU richness was negatively correlated with bacterial production and chlorophyll a concentrations. Unlike the temporal pattern in OTU richness, community composition changed from winter to spring, prior to onset of the summer phytoplankton bloom. Community composition continued to change during the phytoplankton bloom, with increased relative abundance of several taxa associated with phytoplankton blooms, particularly Polaribacter. Bacterial community composition began to revert toward pre-bloom conditions as bacterial production declined. Overall, our findings clearly demonstrate the temporal relationship between phytoplankton blooms and seasonal succession in bacterial growth and community composition. Our study highlights the importance of high-resolution time series sampling, especially during the relatively under-sampled Antarctic winter and spring, which enabled us to discover seasonal changes in bacterial community composition that preceded the summertime phytoplankton bloom.CL was partially funded by the Graduate School and the Department of Ecology and Evolutionary Biology at Brown University and the Brown University-Marine Biological Laboratory Joint Graduate Program. This material is based upon work supported by the National Science Foundation under Grant Nos. ANT-1142114 to LA-Z, OPP-0823101 and PLR-1440435 to HD, and ANT-1141993 to JR

Northern-Most North American Flower Visitation Records of the Introduced Flower Fly, \u3ci\u3eSyritta Flaviventris\u3c/i\u3e (Diptera: Syrphidae) and Comparisons With Sympatric Species, \u3ci\u3eSyritta Pipiens\u3c/i\u3e

We report for the first time the syrphid fly, Syritta flaviventris (Macquart), collected in Lancaster County, Pennsylvania, as the northern-most record for this introduced Mediterranean species. In total, 3 male specimens and 1 female specimen were net collected on three flower species (Verbena hastata, Eryngium yuccifolium and Asclepias incarnata), at a single site of 11 monitored farm sites in southern Pennsylvania. Floral records for the similar introduced sibling species, Syritta pipiens (L.), are presented as well. Passive monitoring with colored pan traps used to monitor bee populations at these sites was not effective in collecting either species of Syritta. Our study suggests that increased active net sampling of Syritta species may provide more information about this genus\u27 distribution in the New World and support future research efforts examining Syritta biology and life history