bluuebunny/crossref_metadata_2025 huggingface dataset:
Decadal‐scale variability in the Kuroshio marine ecosystem in winter
Authors: Nakata Kaoru , Hidaka Kiyotaka
Published: September 2003

Interannual variation of winter copepod biomass during the last three decades of the twentieth century was examined in the Kuroshio, off central Japan in relation to climate regime shifts. The biomass levels of large copepods in the period before 1977 and in 1999 and 2000 were higher than those in the period between 1977 and 1998. The biomass of large copepods was positively related with the Southern Oscillation Index (SOI), in winter in the Northern Hemisphere, which also showed steplike shifts in 1976/77 and 1998/99. The biomass of large copepods was largely influenced by abundance of Calanus sinicus that has high rates of production compared with small copepods under food satiated conditions. Accordingly, the climatic regime shift accompanied by the climatic change in the tropical region seems to regulate interannual variation of winter biomass of large copepods in the Kuroshio through effects on food supply. There is less decadal variablity in the small copepod (SC) biomass than large copepod (LC) biomass, but more variablity in SC than in LC at periods 2–4 years. In contrast to the large copepods, the biomass of small copepods was not related to global climate indices but with the local climate factors such as SST in the Kuroshio and variability in the Kuroshio flow path. Causes for the differences in the biomass trends between large and small copepods are discussed.
Copepod species diversity and climate variability in the tropical Atlantic Ocean
Authors: Piontkovski Sergey A. , Landry Michael R.
Published: September 2003

A database synthesized from 19 oceanographic expeditions conducted by the former Soviet Union was used to analyse interannual patterns in copepod species diversity in the tropical Atlantic. Mesozooplankton was collected predominately in vertical hauls through the upper 100 m with Juday nets. The samples from 744 oceanographic stations were identified and enumerated to the species level. To assess species diversity, the Shannon diversity index was used. On the interdecadal scale, no statistically confirmed trend was found in species diversity change over the years sampled (1963–89). Multiple regression analysis indicated that interannual fluctuations of the South Atlantic High (pressure and latitude), the Azores High longitude and El Niño–Southern Oscillation (ENSO) index could explain 87% of species diversity fluctuations. Possible mechanisms that drive interannual fluctuations of species diversity are discussed.
Decadal‐scale variations of ecosystem productivity and control mechanisms in the Bohai Sea
Authors: Tang Qisheng , Jin Xianshi , Wang Jun , Zhuang Zhimeng , Cui Yi , Meng Tianxiang
Published: September 2003

Decadal‐scale variations of ecosystem productivity in the Bohai Sea are described by using the survey data of 1959–60, 1982–83, 1992–93 and 1998–99. Indices including chlorophyll a concentration, primary production, phytoplankton abundance, zooplankton biomass and fishery biomass were used to describe the ecosystem productivity at different trophic levels. During the past four decades, the productivity and community structure of the Bohai Sea ecosystem has been highly variable. Primary productivity and fish productivity decreased from 1959 to 1998, such that phytoplankton abundance in 1992 and 1998 was about 38% of that in 1959 and 1982, fishery biomass in 1998 was particularly low, which was only about 5% of that in 1959. Zooplankton secondary productivity also showed a decreasing trend from 1959 to 1992, but reached high levels in 1998, about three times as much as 1959 and 1982, and four times as much as 1992. These results indicate that a large variation in ecosystem productivity is one of the important characteristics of coastal ecosystem dynamics. Therefore, it is impossible to apply a single theory to explain the causes of variations in the Bohai Sea ecosystem as the changes in productivity are likely to be forced and/or modulated by multiple mechanisms.
Periodic changes in the zooplankton of the North Sea during the twentieth century linked to oceanic inflow
Authors: Reid Philip C. , Edwards Martin , Beaugrand Gregory , Skogen Morten , Stevens Darren
Published: September 2003

Oceanic inflow is estimated to contribute more than 90% of the nutrient input into the North Sea. Variability in the volume, chemical properties, biological content and source of the inflowing water is thus likely to have a considerable effect on North Sea ecosystems. Changes seen in the plankton, and in particular Calanus finmarchicus and Calanus helgolandicus, over the last 40 years as measured by the Continuous Plankton Recorder survey, allow clear periods to be identified that appear to be associated with variability in inflow. Monthly estimates of inflow and outflow across a section between Orkney and Utsira in Norway as well as netflow (sum of Baltic outflow, runoff and Channel inflow), have been derived from runs of the NORWECOM model for two integrated depth intervals: surface to 150 m and >150 m. A comparison is made between the physical model output and plankton results for the period 1958–99. Distinct plankton periods that appear to reflect changing inflow events are discussed in relation to hydrometeorological and earlier plankton studies over approximately the last 100 years.
Abundance of Calanus sinicus across the tidal front in the Yellow Sea, China
Authors: Liu G. M. , Sun S. , Wang H. , Zhang Y. , Yang B. , Ji P.
Published: September 2003

The abundance of Calanus sinicus eggs, nauplii, copepodites and adults and chlorophyll a (Chl‐a) concentration were studied across tidal fronts in October 2000, and May and June 2001 in the Yellow Sea, China. The aim of the study was to evaluate the role of tidal fronts in the ecology of C. sinicus. The hydrographic tidal fronts were identified by the horizontal temperature gradient in the bottom layer and the temperature profiles across the fronts. The survey results showed that the concentration of Chl‐a was high in the vicinity of the fronts, particularly in spring and early summer. The abundance of C. sinicus eggs and nauplii was usually higher in the tidal fronts than in the adjacent areas. In May and June 2001, the abundance of copepodites and adults of C. sinicus peaked in the tidal front. In June 2001 and October 2000, many copepodites and adults were found in stratified region.
Scale issues in marine ecosystems and human interactions
Authors: Ian Perry R. , Ommer Rosemary E.
Published: September 2003

Understanding the reciprocal interactions between humans and marine ecosystems has several fundamental difficulties, in particular compatible methodologies and different analytical scales. The issue of scale is central, as the scales chosen for studies of marine systems and human interactions can constrain recognition of the drivers and responses of these systems to global changes. The essential task is to discover how to combine social and natural science scale analyses to understand the impact of natural systems on people and the impact of people on natural systems. We identify characteristic spatial, temporal and organizational scales in marine ecosystems and human interactions, and the difficulties inherent in their cross‐disciplinary application. An approach is suggested focusing on communities of fish and fishers that makes explicit: (1) the need to manage marine resources in such a way as to encompass global to local scales; (2) recognition of the complementary nature of organizational scales between the natural and social sciences and use of appropriate natural science scales in the development of management policies; (3) the need to be aware of shifting temporal baselines and the representative nature of the data over time, for both social and natural sciences; and (4) caution regarding predictive models when humans are included. In terms of methodologies, good scale matches occur across large‐scale social and natural science models and surveys, but problems remain in small‐scale qualitative social studies and in cross‐scale studies. Cumulative case studies appear to provide the best approach, although ‘integrating up’ remains a challenge. Natural and social scientists need to work together to identify these issues of ecosystem processes and human interactions, and their appropriate scales.
Habitat selection of overwintering Calanus finmarchicus in the NE Norwegian Sea and shelf waters off Northern Norway in 2000–02
Authors: Halvorsen Elisabeth , Tande Kurt S. , Edvardsen Are , Slagstad Dag , Pedersen Ole Petter
Published: September 2003

The abundance and distribution of overwintering Calanus finmarchicus in the NE Norwegian Sea and shelf waters off North Norway was studied during January for 2000–02. Depth integrated distribution of C. finmarchicus CV showed aggregations with high abundances in the Lofoten Basin and southwest of Tromsøflaket for all three years. The exact location of the aggregation areas and the maximum abundances did, however, vary between the years. The concentrations southwest of Tromsøflaket were almost twofold higher in 2000 at 150 000 ind. m−2 compared to 70 000 and 90 000 ind. m−2 in 2001 and 2002, respectively. Vertical distribution of the animals was similar for the three years, with most of the CVs of the population residing in the depth interval between 700 and 1200 m. Peak abundances of 350 ind. m−3 were found at 850–1000 m west of Tromsøflaket in 2000, whereas in 2001 the maximum abundances were located in the Lofoten Basin at 700–900 m, in the order of 150 ind. m−3. In 2002, the highest concentration of animals was found west of Vesterålen between 1100 and 1200 m, with a concentration of 385 ind. m−3. The vertical and horizontal distribution of C. finmarchicus CV closely followed the hydrographic structures in the area, with the highest abundances associated with cold (<2°C), less saline (34.85–34.9) water with a density of 27.95–28. The patches of high abundance were located in confined areas along the continental shelf slope and in the Lofoten Basin, indicating that the animals may have been extracted from the highly flushed surface areas in late summer during their ontogenetic descent, and trapped in mesoscale physical features in the deep‐water masses throughout the winter. We argue that deep‐water mesoscale anticyclonic eddies, which are frequently formed along the continental slope and in the Lofoten Basin, may provide favourable retention areas for the overwintering population of C. finmarchicus. Consequently, the impact of ocean climate as well as more regional and local effects on the creation and persistence of these mesoscale features is likely to influence the Calanus abundance and advection paths in the following spring and summer.
Annual cycle of zooplankton abundance, biomass and production on the northern Gulf of Alaska shelf, October 1997 through October 2000
Authors: Coyle Kenneth O. , Pinchuk Alexei I.
Published: September 2003

Zooplankton abundance from March through October on the northern Gulf of Alaska shelf in 1998, 1999 and 2000 was dominated by calanoid copepods; the biomass was dominated by calanoids and cnidarians. Although we sampled during the 1997–1998 El Niño, marked interannual differences in the major copepod taxa were not observed. Zooplankton abundance and species composition were influenced primarily by mean water‐column salinity, secondarily by the mean temperature above the thermocline. An annual biomass peak, averaging about 0.5 g wet weight m−3, occurred in May and consisted primarily of the oceanic copepod species Neocalanus cristatus, Neocalanus plumchrus and Neocalanus flemingeri. A second biomass peak, 0.5 g wet weight m−3, was observed in August and consisted mainly of the cnidarian Aequorea spp. Copepod production, estimated from daily growth rates using temperature–body size regressions, peaked in May at about 35 mg C m−2 day−1. Initial calculations suggest an annual copepod production on the order of 6 g C m−2 year−1, probably less than 10% of the annual primary production. The apparent resilience of the zooplankton assemblage on the northern Gulf of Alaska shelf to the 1997–1998 ENSO may have been because of its large geographic separation from the faunal boundary between zooplankton communities in the California Current and North Pacific subarctic gyre.
The marine copepod, Pseudocalanus elongatus, as a mediator between climate variability and fisheries in the Central Baltic Sea
Authors: Möllmann C. , Kornilovs G. , Fetter M. , Köster F.W. , Hinrichsen H.‐H.
Published: September 2003

Pseudocalanus elongatus is a key species in the pelagic zone of the deep basins of the Central Baltic Sea. The copepod serves as a major food organism for larval as well as for adult, pelagic planktivorous fish. Large interannual fluctuations in the standing stock of P. elongatus have been attributed to significant changes in the hydrographic environment over the last two decades. In particular, the decreasing salinity in the Baltic deep basins, a result of a change in atmospheric forcing leading to an increase in rainfall since the 1980s and of a lack of pulses of saline water intrusions from the North Sea, was found to affect reproduction and maturation of the copepod. In parallel, dramatic changes in the weight‐at‐age of herring, one of the most important commercial fishes of the Baltic Sea, have been observed since the late 1980s. Using time‐series on herring stomach contents, as well as length and weight, we provide evidence for a chain of events relating variability in climate, salinity and P. elongatus abundance to changes in diet and condition of herring in the Central Baltic Sea.
Environmental ‘loopholes’ and fish population dynamics: comparative pattern recognition with focus on El Niño effects in the Pacific
Authors: Bakun Andrew , Broad Kenneth
Published: September 2003

A process of comparative pattern recognition is undertaken for the purpose of garnering insights into the mechanisms underlying some currently puzzling conundrums in fishery resource ecology. These include (a) out‐of‐phase oscillations between anchovies and sardines, (b) the remarkable fish productivity of the Peru–Humboldt marine ecosystem, (c) sardine population increases in the eastern Pacific during El Niños, (d) basin‐wide synchronies in large‐amplitude abundance variations, (e) characteristic spawning of large tuna species in poorly productive areas, (f) contrary trends in Pacific tropical tuna abundance during the 1970s and early 1980s.

It is found that each of the items appears to become less enigmatic when the conceptual focus shifts from conventional trophodynamics to the idea that ‘loopholes’ in the fields of biological controls (i.e. of predators of early life stages), produced by poor ocean productivity or by disruptive environmental perturbations, may in fact lead to remarkable reproductive success. Implications include the following: (1) El Niño, rather than being an unmitigated disaster for Peruvian fisheries, may in the long run be a prime reason for the remarkable fishery productivity of the Peru–Humboldt large marine ecosystem. (2) Globally‐teleconnected climatic trends or shifts might produce globally‐coherent population expansions even when local environmental expressions may be quite different. (3) It may be unreasonable to expect any management methodologies to be able to keep the fish populations of highly climatically‐perturbed systems such as the Peruvian LME always at stable high levels; an alternative approach, for example, might be to take optimal advantage of the transient opportunities afforded by the high fish productivity of such inherently erratic systems.
Tidal front and the convergence of anchovy (Engraulis japonicus) eggs in the Yellow Sea
Authors: Hao Wei , Jian Su , Ruijing Wan , Lei Wang , Yi'an Lin
Published: September 2003

Anchovy recruitment determines fish production and thus the sustainable exploitation of anchovy in the Yellow Sea. Haizhou Bay is a traditional spawning and nursery ground for anchovy. The retention of anchovy in its early life stages appears to be related to observed fronts. Cruises have confirmed that anchovy eggs are distributed in high density patches, particularly in the tidal frontal zone. Front and egg patches shift to the shallow area in the warm season. A diagnostic Hamburg Shelf Ocean Model was applied in the East China Sea and Yellow Sea to simulate the frontal circulation and particle movement, forced by monthly wind speed and measured temperatures. It was observed that the jet along the front and upwelling in the mixed side of the front play an important role in the transport of eggs. Convergence and divergence areas are frequently induced by frontal shear instability and topography potential vorticity balance. Numerical experiments show that tidal mixing and front play an important role to converge particles like eggs. When eggs are caught in the convergence zone they are aggregated into a patch. The convergence zone has good feeding condition for eggs to hatch and larvae to grow.
Modelling the vertical distribution of eggs of anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus)
Authors: Boyra G. , Rueda L. , Coombs S.H. , Sundby S. , Ådlandsvik B. , Santos M. , Uriarte A.
Published: September 2003

Understanding and modelling the vertical distribution of fish eggs in the water column is a major challenge for future use of underway‐continuous egg samplers as estimators of the total egg abundance. This study presents modelling of field data of anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus) egg vertical distribution obtained from LHPR sampling in the Bay of Biscay. Starting from Sundby's model [Deep‐Sea Res.30 (1983) 645], improvements were achieved through successive modifications concerning egg buoyancy and vertical propagation of wind‐induced turbulence. In addition, measurements of egg settling velocity and buoyancy by stages were included as inputs for the model. The best model fitting was achieved through the adoption of a gradual turbulence vertical decay model (proportional to the inverse of the water density profile), a Gaussian variability of egg density and adaptability of the egg density to the surrounding water by means of permeability of the chorion. This led to improvements over the Sundby original model. The coefficient of determination (R2) of the modelled egg abundance profiles compared with the observed ones was around 80% for both sardine and anchovy. The model described successfully the vertical distribution of eggs for waters of high surface salinity (R2 of almost 90%), but less so for waters of low surface salinity (R2 of about 70%).
Effects of ontogenetic vertical migration of zooplankton on annual primary production – using NEMURO embedded in a general circulation model
Authors: Aita Maki N. , Yamanaka Yasuhiro , Kishi Michio J.
Published: September 2003

We developed a global three‐dimensional physical–biological coupled model and applied it in simulations with and without ontogenetic seasonal vertical migration of large zooplankton (copepods). The annual cycle of phytoplankton behaviour is well reproduced by this model with the seasonal vertical migration of zooplankton. A comparison of the two cases shows that in the northwestern Pacific and subarctic southern ocean, primary production is higher in the case with vertical migration. In these regions, large phytoplankton (diatoms) dominate, and the presence of large zooplankton throughout the year reduces primary production by large phytoplankton (diatoms). This effect is greatest for the diatom bloom. On the other hand, for regions where small phytoplankton dominate, primary production is higher in the case without vertical migration. This is because small zooplankton are suppressed by grazing pressure from large zooplankton, reducing grazing pressure on small phytoplankton.
Recruitment, sustainable yield and possible ecological consequences of the sharp decline of the anchovy (Engraulis japonicus) stock in the Yellow Sea in the 1990s
Authors: Zhao X. , Hamre J. , Li F. , Jin X. , Tang Q.
Published: September 2003

Natural mortality, stock–recruitment relationship and sustainable yield of the anchovy (Engraulis japonicus) stock in the Yellow Sea were estimated based on acoustic assessments of the wintering anchovy stock from 1987 to 2002. The stock‐recruitment relationship was estimated to be: R = 151.1 × SSB × e−0.299·SSB, where R is given in billion fish and SSB is in million tons. The optimum sustainable yield of anchovy was estimated at 520 000 tons for the period 1987–2002. The ecological consequences of the sharp decline of the anchovy stock observed after 1996 were examined in terms of the reduction in biomass production in the Yellow Sea ecosystem, as well as the consequences of such reduction on predator–prey interactions and species competition.
Growth rate variability of Pacific saury, Cololabis saira, larvae in the Kuroshio waters
Authors: Oozeki Yoshioki , Watanabe Yoshiro , Kurita Yutaka , Nakata Kaoru , Kitagawa Daiji
Published: September 2003

Growth rate time series of Pacific saury, Cololabis saira, larvae in the Kuroshio waters were constructed using a previously reported relationship between early life stage growth rates and environmental factors in winter (January to March) 1971–2000, including sea surface temperature, chlorophyll a concentration and copepod density. Pacific saury has been commercially exploited and its stock size shows large fluctuations. It spawns from autumn to spring. Growth and survival in the early life stage have been considered the major factors controlling recruitment fluctuations. The winter spawning cohort showed a fast and stable growth rate during their early stage. Ages of 40 mm juveniles (t40) calculated from growth rate estimations were stable during the 30‐yr period and showed a significant positive correlation to the Pacific Decadal Oscillation index in winter. A negative correlation between the t40 and the catch record of medium size saury (24.0–28.9 cm) was detected but was not significant. Recruitment of the winter spawning cohort is thought to be regulated not only by the duration of the vulnerable larval period but also by other biological factors, i.e. mortality after the larval stage and the abundance of predators.
Wind strength and biological productivity in upwelling systems: an idealized study
Authors: Botsford Louis W. , Lawrence Cathryn A. , Dever Edward P. , Hastings Alan , Largier John
Published: September 2003

Biological production in wind‐driven coastal upwelling systems is of global importance. To understand better how wind speed and shelf width affect productivity, we formulated a simple model of cross‐shelf transport that included the dynamics of one potential mechanism: increasing nutrients with increasing winds, with possible loss of productivity due to off‐shelf Ekman transport. We used this model to determine how shelf productivity would depend on wind speed and shelf width using several ecosystem (Nutrient–Phytoplankton–Zooplankton, NPZ) models that reflect different trophic pathways and differences in model stability. For constant wind speeds, shelf productivity for all of the NPZ models declined beyond a certain wind speed. The shelf transit time beyond which productivity declines can be determined graphically from the time course of cumulative production in the NPZ model. Shelf width and latitude then determine the corresponding wind speed. The predicted points of decline in productivity with wind‐speed were consistent with data from local observations of higher trophic levels on the central California coast. Only shelf productivity of the NPZ model reflecting new production was dome‐shaped. Shelf productivity of models of regenerated production remained constant with wind speed at low winds. Artificial instability in NPZ models can lead to an inaccurate dependence of productivity on wind. Our model of coastal upwelling, which represents production as cross‐shelf transport of parcels containing developing NPZ models, exhibits a different dependence on wind forcing than previous models that represented upwelling production as a fully mixed shelf. The relative degree of mixing versus transport in upwelling systems is a critical factor underlying the dependence of productivity on wind.
Modelling the distribution, sustainability and diapause emergence timing of the copepod Calanus finmarchicus in the Labrador Sea
Authors: Tittensor D. P. , DeYoung B. , Tang C. L.
Published: September 2003

It is now recognized that Calanus finmarchicus, the dominant copepod zooplankter of the North Atlantic, has most of its biomass in the open ocean. While the Labrador Sea does contain a large population of Calanus finmarchicus, the importance of possible connections with the rest of the North Atlantic are not understood. Although there are few wintertime observations, sufficient data exist to model the role of the circulation, temperature and food supply on population dynamics. This study couples a biological model of Calanus finmarchicus with a physical oceanographic model of the Labrador Sea, using chlorophyll data derived from observations by the satellite‐borne SeaWiFS (Sea‐viewing Wide Field‐of‐view Sensor) as a proxy food supply for the numerical copepods. We produce a large‐scale, comprehensive picture of the spatial distribution of Calanus finmarchicus in the Labrador Sea, along with an exploration of the timing of diapause and an examination of population sustainability. We are able to simulate reasonably well the temporal and spatial patterns of Calanus finmarchicus in the Labrador Sea. During a year long model run, the population has a single generation over most of the Labrador Sea, with a final diapausing population about 50% the size of the initial for the parameters used in these simulations. A latitudinally dependent diapause emergence scheme with early emergence to the south of Newfoundland provides the best fit to data. A change of 0.5°C in the temperature field can cause significant changes in the population abundance in a single year, due to changes in Calanus finmarchicus growth rates.
Hydrodynamic model forecasts as a guide for process studies on plankton and larval fish
Authors: Pedersen Ole P. , Slagstad Dag , Tande Kurt S.
Published: September 2003

The interaction between hydrography, zooplankton and capelin larvae was studied during a 15‐day survey in May 2001 in the southern part of the Barents Sea within the strategic programme Capelin and Herring in the Barents Sea Coexistence or Exclusion (BASECOEX). The spawning ground of capelin is found on shallow grounds close to the coast and after hatching the fish larvae are being transported offshelf towards the central part of the Barents Sea. The objective of the field study was to provide estimates of mortality and growth during the duration of the survey. Estimating vital rates requires sampling upon the same population over time. Areas feasible for studying these processes for capelin larvae would have to fulfil several conditions, such as moderate advection, high population numbers of larvae together with appropriate sampling techniques. This paper describes how a model approach may be used as a guideline for planning and executing a survey which has to meet the above conditions. Initially, the biological field was nowcasted with an Individual Based Model (IBM) at the start of the survey. The hydrodynamic model used in conjunction with the IBM required realistic weather forcing. Because of collecting and processing of the data, they are always lagging 1–2 days behind the current date. In order to solve the problem of nowcasting and forecasting we applied real data as far as we could and continued with forecasted weather for the next 5 days. This map was then utilized at sea as part of the information needed to decide where to place the sampling grid, and in the design of the layout of the grid. The model approach further enabled us to estimate the retention of water masses and consequently the capelin larvae and zooplankton populations within the region of study. The retention analysis shows that the advection in the selected area is significant, and after 2 weeks only a small fraction of the initial population is present in the original grid.
Relative resistance of Pacific salmon to infectious salmon anaemia virus
Authors: Rolland J B , Winton J R
Published: September 2003

Infectious salmon anaemia (ISA) is a major disease of Atlantic salmon, Salmo salar, caused by an orthomyxovirus (ISAV). Increases in global aquaculture and the international movement of fish made it important to determine if Pacific salmon are at risk. Steelhead trout, Oncorhynchus mykiss, and chum, O. keta, Chinook, O. tshawytscha, coho, O. kisutch, and Atlantic salmon were injected intraperitoneally with a high, medium, or low dose of a Norwegian strain of ISAV. In a second challenge, the same species, except chum salmon, were injected with a high dose of either a Canadian or the Norwegian strain. Average cumulative mortality of Atlantic salmon in trial 1 was 12% in the high dose group, 20% in the medium dose group and 16% in the low dose group. The average cumulative mortality of Atlantic salmon in trial 2 was 98%. No signs typical of ISA and no ISAV‐related mortality occurred among any of the groups of Oncorhynchus spp. in either experiment, although ISAV was reisolated from some fish sampled at intervals post‐challenge. The results indicate that while Oncorhynchus spp. are quite resistant to ISAV relative to Atlantic salmon, the potential for ISAV to adapt to Oncorhynchus spp. should not be ignored.
Melano‐macrophage centres and their role in fish pathology
Authors: Agius C , Roberts R J
Published: September 2003

Melano‐macrophage centres, also known as macrophage aggregates, are distinctive groupings of pigment‐containing cells within the tissues of heterothermic vertebrates. In fish they are normally located in the stroma of the haemopoietic tissue of the spleen and the kidney, although in amphibians and reptiles, and some fish, they are also found in the liver. They may also develop in association with chronic inflammatory lesions elsewhere in the body and during ovarian atresia. In higher teleosts, they often exist as complex discrete centres, containing lymphocytes and macrophages, and may be primitive analogues of the germinal centres of lymph nodes. Melano‐macrophage centres usually contain a variety of pigments, including melanins, and these increase in range and volume in older fish or in the presence of cachectic disease. Melano‐macrophage centres act as focal depositories for resistant intracellular bacteria, from which chronic infections may develop. Iron capture and storage in haemolytic diseases appears to be a primary function, but antigen trapping and presentation to lymphocytes, sequestration of products of cellular degradation and potentially toxic tissue materials, such as melanins, free radicals and catabolic breakdown products are among other functions that have been ascribed. Recent work suggests that they are a site of primary melanogenesis rather than mere storage. Melano‐macrophage centres increase in size or frequency in conditions of environmental stress and have been suggested as reliable biomarkers for water quality in terms of both deoxygenation and iatragenic chemical pollution.
Extra small virus‐like particles (XSV) and nodavirus associated with whitish muscle disease in the giant freshwater prawn,Macrobrachium rosenbergii
Authors: Qian D , Shi Z , Zhang S , Cao Z , Liu W , Li L , Xie Y , Cambournac I , Bonami J‐R
Published: September 2003

A disease ofMacrobrachium rosenbergii, the giant freshwater prawn, farmed in China was recently recorded in Zhejiang, Jiangsu, Shanghai, Guangxi and Guangdong provinces. The clinical sign of the disease, which develops in post‐larvae (PL), is a whitish appearance of the muscles, particularly noticeable in the abdomen. Mortalities may reach 100% in some hatcheries. Investigations by transmission electron microscopy after negative staining of diseased PL homogenates showed the presence of two types of viral particles: one, unenveloped, icosahedral in shape, 26–27 nm in diameter, the second, much smaller, about 14–16 nm in diameter, designated extra small virus particle (XSV). The large virus has a genome with two pieces of ssRNA (RNA‐1 and RNA‐2), of 3 and 1.2 kb, respectively. Hybridization tests confirmed that this large virus is closely related toM. rosenbergiinodavirus (MrNV) which was isolated from diseased prawns in a hatchery in the French West Indies. Its very small size and hypothesized biochemical and biological characteristics suggest XSV is a new type of crustacean virus. As XSV has always been found associated with the larger virus (nodavirus) and is located in muscle and connective cells of diseased animals, it could be an autonomous virus, a helper‐type virus or a satellite‐like virus.
Pathology and immunohistochemistry in three species of salmonids after experimental infection with Flavobacterium psychrophilum
Authors: Ekman E , Norrgren L
Published: September 2003

Rainbow trout, Oncorhynchus mykiss (Walbaum), sea trout, Salmo trutta L., and Atlantic salmon, Salmo salar L., were experimentally infected with Flavobacterium psychrophilum in order to evaluate any species differences in susceptibility to the bacterium. Furthermore, differences in pathological changes and distribution of the bacteria in internal organs were studied. The bacteria were injected intraperitoneally in two doses, high dose (Hd) 1 × 107 colony forming units (CFU) fish−1 and low dose (Ld) 1 × 106 CFU fish−1. The mortalities in the Ld groups varied between 0 and 7.5% and in the Hd groups between 55–70%. No significant differences in mortality between the species were recorded. Clinical signs and pathological findings were similar in the three species and in accordance with those of rainbow trout fry syndrome. Rainbow trout showed more pronounced lesions in the spleen compared with the other species. Necrosis of renal tubular epithelium and haematopoietic tissue was most prominent in rainbow trout and Atlantic salmon. Intracellular eosinophilic droplets in the kidney tubular epithelium were a prominent finding in rainbow trout and sea trout surviving the infection. The distribution of the bacteria in internal organs was similar in the three species, as studied with immunohistochemistry.
Feed deprivation of channel catfish, Ictalurus punctatus (Rafinesque), influences organosomatic indices, chemical composition and susceptibility to Flavobacterium columnare
Authors: Shoemaker C A , Klesius P H , Lim C , Yildirim M
Published: September 2003

Withholding feed has been suggested as a strategy to manage infectious disease of channel catfish, Ictalurus punctatus (Rafinesque). In a previous study, we demonstrated that deprivation of feed for as little as 7 days reduced innate resistance of catfish to Flavobacterium columnare. This study was conducted to evaluate the effect of feeding regimens [no feeding (NF), fed once every other day to satiation (FEOD) and fed once daily to satiation (FD)] on organosomatic indices, physiological changes and susceptibility of channel catfish to F. columnare. Fish that were not fed for 2 and 4 weeks had a significant increase (P < 0.05) in gutted weight:wet weight ratio and decrease in other organosomatic indices [gut index (GI), mesenteric fat index (MFI) and hepatosomatic index (HSI)]. Haematology was not effected by feeding regimen except at week 4, when a significantly higher haemoglobin level was observed in the NF fish. Serum protein did not differ at week 2, but the level at week 4 of the NF fish (35.91 mg mL−1) was significantly lower than that of the FD fish (41.77 mg mL−1). Significantly lower (P < 0.05) blood glucose (39.5 and 40.3 mg dL−1) and liver glycogen (1.7 and 1.8 mg g−1) were seen in the NF fish at weeks 2 and 4, respectively, as compared with blood glucose and liver glycogen levels of FD fish (67.5 and 92.8 mg dL−1 and 46.5 and 52.6 mg g−1 at weeks 2 and 4, respectively) and FEOD (82.8 and 85.5 mg dL−1 and 45.1 and 51.4 mg g−1 at weeks 2 and 4, respectively). Mortality in the NF fish caused by F. columnare (78%) was significantly higher (P < 0.05) than mortality in the FD and FEOD treatments (0.0 and 1.7%, respectively). Blood glucose and liver glycogen showed the same trend of low values for NF fish following challenge (week 6). Blood glucose, liver glycogen, GI and HSI are sensitive indicators for channel catfish deprived of feed (NF) for 4 weeks. Blood glucose and liver glycogen levels around 40 mg dL−1 and 2 mg g−1, respectively, are indicative of starvation in juvenile channel catfish. Moreover, NF fish were susceptible to F. columnare infection. Thus, it is suggested that in the absence of natural food, juvenile channel catfish should be fed at least once every other day to apparent satiation to maintain normal physiological function and improve resistance to F. columnare.
A comparison of epidemiological patterns of salmon lice, Lepeophtheirus salmonis, infections on farmed Atlantic salmon, Salmo salar L., in Norway and Scotland
Authors: Heuch P A , Revie C W , Gettinby G
Published: September 2003

This paper examines two large national data sets collected over several years and contrasts the patterns of sea lice, Lepeophtheirus salmonis (Krøyer, 1837), infections, the use of treatments and the occurrence of chalimus peaks between Norwegian and Scottish farms. Infection levels in Scotland were significantly higher in general over the period under study. For the chalimus stage group in the first quarter of the year, Norwegian mean abundance stayed below 10 lice per m2 while Scottish means reached 45 lice per m2 of fish skin per m3 of water. Both countries had more chalimus in summer than at other times of year, but in the last 3 months of the year Scottish fish had, on average, two to four times as many chalimus as Norwegian fish. Peaks of chalimus abundance were more frequent in Scotland, particularly in winter, but the most prominent peaks occurred in summer in both countries. In Scotland a marked mid‐year build‐up of mobile pre‐adult and adult stages was seen, and both countries showed a tendency for mobile counts on the second year fish to increase towards the end of the year. Scottish fish carried, on average, three times as many mobile lice per m2 of skin as Norwegian fish in the last 3 months of the year. The difference in lice loads was reflected in the greater use of veterinary medicines on Scottish farms. The higher infection levels in Scotland may be due to shallower and more enclosed water bodies used for farming, smaller and shallower pens, differences in sea water temperatures or in access to appropriate medication. The results highlight the importance of ensuring that effective veterinary medicines are available in the UK for the control of infection.
Lethality of bypass polymerases in Escherichia coli cells with a defective clamp loader complex of DNA polymerase III
Authors: Viguera Enrique , Petranovic Mirjana , Zahradka Davor , Germain Karine , Ehrlich Dusko S. , Michel Bénédicte
Published: September 2003

Escherichia coli DNA polymerase III (Pol III) is one of the best studied replicative DNA polymerases. Here we report the properties of an E. coli mutant that lacks one of the subunits of the Pol III clamp loader complex, Psi (ψ), as a result of the complete inactivation of the holD gene. We show that, in this mutant, chronic induction of the SOS response in a RecFOR‐dependent way leads to lethality at high temperature. The SOS‐induced proteins that are lethal in the holD mutant are the specialized DNA polymerases Pol II and Pol IV, combined with the division inhibitor SfiA. Prevention of SOS induction or inactivation of Pol II, Pol IV and SfiA encoding genes allows growth of the holD mutant, although at a reduced rate compared to a wild‐type cell. In contrast, the SOS‐induced Pol V DNA polymerase does not participate to the lethality of the holD mutant. We conclude that: (i) Psi is essential for efficient replication of the E. coli chromosome; (ii) SOS‐induction of specialized DNA polymerases can be lethal in cells in which the replicative polymerase is defective, and (iii) specialized DNA polymerases differ in respect to their access to inactivated replication forks.
Biofilm formation at the air–liquid interface by the Pseudomonas fluorescens SBW25 wrinkly spreader requires an acetylated form of cellulose
Authors: Spiers Andrew J. , Bohannon John , Gehrig Stefanie M. , Rainey Paul B.
Published: September 2003

The wrinkly spreader (WS) genotype of Pseudomonas fluorescens SBW25 colonizes the air–liquid interface of spatially structured microcosms resulting in formation of a thick biofilm. Its ability to colonize this niche is largely due to overproduction of a cellulosic polymer, the product of the wss operon. Chemical analysis of the biofilm matrix shows that the cellulosic polymer is partially acetylated cellulose, which is consistent with predictions of gene function based on in silico analysis of wss. Both polar and non‐polar mutations in the sixth gene of the wss operon (wssF ) or adjacent downstream genes (wssGHIJ ) generated mutants that overproduce non‐acetylated cellulose, thus implicating WssFGHIJ in acetylation of cellulose. WssGHI are homologues of AlgFIJ from P. aeruginosa, which together are necessary and sufficient to acetylate alginate polymer. WssF belongs to a newly established Pfam family and is predicted to provide acyl groups to WssGHI. The role of WssJ is unclear, but its similarity to MinD‐like proteins suggests a role in polar localization of the acetylation complex. Fluorescent microscopy of Calcofluor‐stained biofilms revealed a matrix structure composed of networks of cellulose fibres, sheets and clumped material. Quantitative analyses of biofilm structure showed that acetylation of cellulose is important for effective colonization of the air–liquid interface: mutants identical to WS, but defective in enzymes required for acetylation produced biofilms with altered physical properties. In addition, mutants producing non‐acetylated cellulose were unable to spread rapidly across solid surfaces. Inclusion in these assays of a WS mutant with a defect in the GGDEF regulator (WspR) confirmed the requirement for this protein in expression of both acetylated cellulose polymer and bacterial attachment. These results suggest a model in which WspR regulation of cellulose expression and attachment plays a role in the co‐ordination of surface colonization.
The Pseudomonas aeruginosa quinolone signal molecule overcomes the cell density‐dependency of the quorum sensing hierarchy, regulates rhl‐dependent genes at the onset of stationary phase and can be produced in the absence of LasR
Authors: Diggle Stephen P. , Winzer Klaus , Chhabra Siri Ram , Worrall Kathryn E. , Cámara Miguel , Williams Paul
Published: September 2003

In Pseudomonas aeruginosa, diverse exoproduct virulence determinants are regulated via N‐acylhomoserine lactone‐dependent quorum sensing. Here we show that 2‐heptyl‐3‐hydroxy‐4(1H)‐quinolone (PQS) is also an integral component of the quorum sensing circuitry and is required for the production of rhl‐dependent exoproducts at the onset of stationary phase. Analysis of spent P. aeruginosa culture supernatants revealed that PQS is produced at the end of exponential phase in the parent strain and in the late stationary phase of a lasR mutant. Mutants defective in both PQS production (pqsR‐) and response (pqsE‐) produced substantially reduced levels of exoproducts but retained wild‐type N‐butanoyl homoserine lactone (C4‐HSL) levels. In the wild type, provision of exogenous PQS at the time of inoculation significantly increased PA‐IL lectin, pyocyanin and elastase production during early stationary phase and promoted biofilm formation. Exogenous PQS but not PQS derivatives lacking the 3‐hydroxy group overcame the cell density but not growth phase‐dependent production of exoproducts. PQS also overcame the transcriptional and post‐transcriptional repression of lecA (which codes for the PA‐IL lectin) mediated via the negative regulators MvaT and RsmA respectively. Increased expression of lecA in the presence of exogenous PQS can be explained partially by increases in RhlR, RpoS and C4‐HSL levels. A refined model for quorum sensing in P. aeruginosa is presented.
Cationic antimicrobial peptides activate a two‐component regulatory system, PmrA‐PmrB, that regulates resistance to polymyxin B and cationic antimicrobial peptides in Pseudomonas aeruginosa
Authors: McPhee Joseph B. , Lewenza Shawn , Hancock Robert E. W.
Published: September 2003

The two‐component regulatory system PhoP‐PhoQ of Pseudomonas aeruginosa regulates resistance to cationic antimicrobial peptides, polymyxin B and aminoglycosides in response to low Mg2+ conditions. We have identified a second two‐component regulatory system, PmrA‐PmrB, that regulates resistance to polymyxin B and cationic antimicrobial peptides. This system responds to limiting Mg2+, and is affected by a phoQ, but not a phoP mutation. Inactivation of the pmrB sensor kinase and pmrA response regulator greatly decreased the expression of the operon encoding pmrA‐pmrB while expression of the response regulator pmrA in trans resulted in increased activation suggesting that the pmrA‐pmrB operon is autoregulated. Interposon mutants in pmrB, pmrA, or in an intergenic region upstream of pmrA‐pmrB exhibited two to 16‐fold increased susceptibility to polymyxin B and cationic antimicrobial peptides. The pmrA‐pmrB operon was also found to be activated by a number of cationic peptides including polymyxins B and E, cattle indolicidin and synthetic variants as well as LL‐37, a component of human innate immunity, whereas peptides with the lowest minimum inhibitory concentrations tended to be the weakest inducers. Additionally, we showed that the putative LPS modification operon, PA3552‐PA3559, was also induced by cationic peptides, but its expression was only partially dependent on the PmrA‐PmrB system. The discovery that the PmrA‐PmrB two‐component system regulates resistance to cationic peptides and that both it and the putative LPS modification system are induced by cationic antimicrobial peptides has major implications for the development of these antibiotics as a therapy for P. aeruginosa infections.
IcsA, a polarly localized autotransporter with an atypical signal peptide, uses the Sec apparatus for secretion, although the Sec apparatus is circumferentially distributed
Authors: Brandon Lauren D. , Goehring Nathan , Janakiraman Anuradha , Yan Arthur W. , Wu Tong , Beckwith Jon , Goldberg Marcia B.
Published: September 2003

Asymmetric localization of proteins is essential to many biological functions of bacteria. Shigella IcsA, an outer membrane protein, is localized to the old pole of the bacillus, where it mediates assembly of a polarized actin tail during infection of mammalian cells. Actin tail assembly provides the propulsive force for intracellular movement and intercellular dissemination. Localization of IcsA to the pole is independent of the amino‐terminal signal peptide (Charles, M., Perez, M., Kobil, J.H., and Goldberg, M.B., 2001, Proc Natl Acad Sci USA 98: 9871–9876) suggesting that IcsA targeting occurs in the bacterial cytoplasm and that its secretion across the cytoplasmic membrane occurs only at the pole. Here, we characterize the mechanism by which IcsA is secreted across the cytoplasmic membrane. We present evidence that IcsA requires the SecA ATPase and the SecYEG membrane channel (translocon) for secretion. Our data suggest that YidC is not required for IcsA secretion. Furthermore, we show that polar localization of IcsA is independent of SecA. Finally, we demonstrate that while IcsA requires the SecYEG translocon for secretion, components of this apparatus are uniformly distributed within the membrane. Based on these data, we propose a model for coordinate polar targeting and secretion of IcsA at the bacterial pole.