bluuebunny/crossref_metadata_2025 huggingface dataset:
Population dynamics of the brown shrimp Crangon crangon L., in shallow areas of the German Wadden Sea
Authors: DEL NORTE‐CAMPOS A. G. C. , TEMMING A.
Published: March 2003

Settlement, growth and mortality of the brown shrimp, Crangon Crangon L., were studied in the north Frisian Wadden Sea over a period of 19 months to fill existing gaps regarding the species' life cycle, and thereby to clarify points related to the fishery. Settlement of postlarval shrimp in the shallow areas occurred in three batches: in May; during summer; and an overwintering batch. Compared with an earlier model based on laboratory‐derived data, a new growth model based on field data predicts similar growth rates for the earlier phase of the shrimp life cycle, but higher rates for the later stages of the cohorts. Mean growth rate of the different cohorts over the size range sampled was 0.23 ± 0.08 mm day−1. Of the factors tested, only temperature significantly influenced growth rates. Preliminary estimates of instantaneous total mortality values for shrimp cohorts from these shallow areas ranged from 0.03 to 0.12 day−1. Salinity explained most of the variation in mortality rates, but this most likely indicates an indirect effect of depth on emigration. The cumulative effects of growth rates estimated from the new model and lower losses through predation could imply a higher contribution of winter eggs to the autumn fishery. This, however, needs further evaluation to properly quantify the trade‐offs between settlement and recruitment to the fishery, as well as the growth and mortality rates.
The onset of spawning in the silver pomfret, Pampus argenteus (Euphrasen), in Kuwait waters and its implications for management
Authors: DADZIE S. , ABOU‐SEEDO F. , AL‐SHALLAL T.
Published: March 2003

Abstract The spawning periodicity of silver pomfret, Pampus argenteus (Euphrasen), was investigated against a background of conflicting evidence on the onset of spawning in this species. Contrary to the existing view that silver pomfret in Kuwait waters begin to spawn in March–April, evidence is presented that indicates a delay in spawning until May. Only an insignificant level of spawning takes place in April which, from the management point of view, may be ignored. The species has a prolonged spawning period extending from May to August in females, although the males mature in April and ripe specimens are encountered in monthly samples until September. There are two spawning peaks, the first one in May and the second in August.
Relationships between marine growth and marine survival of one sea winter Atlantic salmon, Salmo salar L., from the River Bush, Northern Ireland
Authors: Crozier W. W. , Kennedy G. J. A.
Published: March 2003

An examination of marine growth/marine survival relationships in Atlantic salmon, Salmo salar L., was carried out, based on scale growth measurements in relation to two indices of marine survival in wild fish from the River Bush, Northern Ireland. The survival of cohorts to the Irish/Northern Irish coast (prefishery) and to fresh water was statistically unrelated to variation in growth from smolt migration to the end of the first winter at sea (P > 0.1; –P > 0.7). Marine growth of 1+ smolts decreased significantly during the period of the study (P < 0.05), but growth of 2+ smolts did not change (P > 0.05). The variability in marine growth was much less than the variation in natural survival at sea, suggesting that factors instead of or in addition to, growth influence natural survival in the marine environment. Survival to fresh water was not related to survival to the coast (P > 0.4), although it was inversely correlated with exploitation rate (P < 0.01). These results are discussed in relation to the use of freshwater returns to assess marine survival and the potential for the variation in natural marine mortality to influence total life‐cycle variation.
Morphometric relationships and indirect determination of the length frequency structure of the pirarucu, Arapaima gigas (Cuvier), in Brazilian Amazonia
Authors: MARTINELLI N. M. C. , PETRERE M.
Published: March 2003

Abstract  The pirarucu (giant red fish), Arapaima gigas (Cuvier), (Arapaimidae) is among the diverse fish resources of Amazonia which are threatened by over‐exploitation. Little is known about the biology of this species despite its commercial importance. The present paper provides indirect information about the length‐frequency structure of the stock which was estimated by sampling its tongue bone in craft shops and weighing fresh mantas (processed fish product) in fish markets since these were the only remaining recognizable features of the fish. The length‐frequency reconstruction was carried out using a regression analysis calculated by utilizing individuals caught in experimental fishing.
Development of inland aquaculture in arid climates: water utilization strategies applied in Israel
Authors: Mires D.
Published: March 2003

Israel has a temperate climate with marked differences between the northern and southern regions. Rainfall ranges between 250 and 600 mm year−1 in the former and between only 25 and 200 mm year−1 in the latter. During the last 30 years, water consumption has increased markedly in all sectors. Although a water allocation for inland aquaculture is made, in most cases it is given the lowest priority, and aquaculturists have learned to contend with difficulties, and thrive on brackish water sources not fit for human consumption or agricultural crops. Since most water sources are already fully exploited, further development of all sectors will depend on their respective capacity to use recycled city water, desalinated brackish or sea water, or recycled pond water. In this respect, inland aquaculture is handicapped by public prejudices which will not allow the use of water from the first source and farms are still not able to cope with the cost of the second. Therefore, further development of inland aquaculture will depend on the capacity of farmers to use sea water, and to recycle pond water time and again to produce more fish with less (inland) water. Various strategies have already been developed in Israel and new ones are under study. These include water harvesting in dual‐purpose reservoirs, recycling of pond water from one year to another, development of intensive flow‐through systems based on recycled pond water and colleagues based on biofiltration.
Status of the crucian carp, Carassius carassius (L.), in the UK
Authors: Wheeler A.
Published: March 2003

The crucian carp, Carassius carassius (L.), is a small fish of restricted distribution in the UK, which is probably only native to central and eastern England. The crucian carp is endemic to northern Europe. It has been widely confused with the introduced and congeneric goldfish, Carassius auratus (L.), and forms hybrids with that species and the introduced Cyprinus carpio L. The status of this fish has become confused with the presence of the congener and its hybrids, and it is now thought to be less frequent in occurrence than formerly.
Social and financial aspects of the artisanal fisheries of Middle São Francisco River, Minas Gerais, Brazil
Authors: De Camargo S. A. Franco , Petrere JR M.
Published: March 2003

The presence or absence of motorized boats, partnerships and multispecies catches characterize the fisheries of São Francisco River, Minas Gerais, Brazil. Fishing activity based on 109 interviews, carried out in the wet (high water: February and March) and dry (low water: July and August) seasons, with professional fishermen are described. Aiming to identify the fishery income components, a covariance model was proposed, with the income as the response variable, related to the factors: fishing ground; use of motorized or paddle boat; seasonality; presence of fishing assistant; and the following covariates: capture in weight in the week prior to the interview; fisherman experience in yrs; and distance (km) travelled for fishing. The results indicated that the main contributions to income were the absence of an engine (because of high price of the fuel), the absence of a partner (because of low capture) and the amount of fish caught by the fishermen.
Instream and catchment characteristics affecting the occurrence and population density of brown trout, Salmo trutta L., in forest brooks of a boreal river basin
Authors: Jutila E. , Ahvonen A. , Julkunen M.
Published: March 2003

The occurrence and density of ≥ 1+ brown trout, Salmo trutta L., and their relationship with prevailing instream and catchment characteristics were studied in 50 small forest streams, partially dredged for forest ditching. The occurrence of trout at a stream site was largely determined by the abundance of pools, size of upper catchment and water pH. Moreover, at sites where trout occurred, the abundance of pools was lower at dredged locations than at those in a natural state. In riffles in a natural state, there was a positive relationship between trout density and three instream variables: the abundance of stream pools, cascades and instream vegetation, while an inverse relationship was found with the abundance of substratum of 2–10 cm in diameter. Of the catchment variables, correspondingly, the proportion of forest in the upper catchment was positively related and the proportion of peatland negatively related to trout density. No significant regression model could be fitted for dredged riffles. The possibility of enhancing trout populations in dredged riffles is discussed.
The efficacy of air, sound and acoustic bubble screens in deflecting Atlantic salmon, Salmo salar L., smolts in the River Frome, UK
Authors: WELTON J. S. , BEAUMONT W. R. C. , CLARKE R. T.
Published: March 2003

Atlantic salmon, Salmo salar L., smolts are vulnerable to entrainment in a variety of man‐made structures as they migrate downstream. The ability of acoustic bubble screens to deflect smolts from potential hazards was assessed. Screens were deployed, in turn, across one of the two identical channels through which the millstream of the River Frome flowed and the efficiency of these screen systems was tested by counting smolts by video recording in each channel. It was concluded that these screens deflected a significant number of smolts. Efficiencies were greater at night than in daylight because of smolt behaviour.
Prey selection and diets of bluegill Lepomis macrochirus with differing population characteristics in two Nebraska natural lakes
Authors: Olson N. W. , Paukert C. P. , Willis D. W. , Klammer J. A.
Published: March 2003

Abstract
 Environmental prey samples and stomach contents of bluegill
Lepomis macrochirus (Rafinesque) were collected in spring and summer 2000 from two Nebraska Sandhill lakes. Watts Lake contained a low‐density bluegill population, whereas Cozad Lake contained a high‐density bluegill population. Bluegill diets from both lakes were compared to determine if bluegill prey preference differed between the two populations. The highest median per cent (by calories) of zooplankton in the diet was 1.3%; the remainder was macroinvertebrates. Watts Lake bluegills preferred (based on Manly's alpha) amphipods in spring and chironomids in summer. Cozad Lake bluegills did not show a strong preference (compared with Watts Lake) for any macroinvertebrates, but still utilized amphipods and chironomids during both seasons. Larger bluegills in Watts Lake preferred chironomids in summer, but Cozad Lake bluegills did not exhibit this relationship. The higher density Cozad Lake bluegill population appeared to be more opportunistic than the lower density Watts Lake population, but both preferred macroinvertebrates.
Oceanographic influences on the distribution of Baltic cod, Gadus morhua, during spawning in the Bornholm Basin of the Baltic Sea
Authors: TOMKIEWICZ JONNA , LEHMANN KLAUS M. , JOHN MICHAEL A. ST.
Published: March 2003

The Baltic Sea is a stratified, semienclosed sea typified by a low‐salinity surface layer and a deep saline layer of varying volume, salinity, temperature and oxygen concentration. The relationships between these oceanographic factors and the distribution of Baltic cod are presented, utilizing results from a survey carried out during the 1995 spawning period in the Bornholm Basin, at present the main spawning area of this stock. Cod distribution, abundance and population structure were estimated from hydroacoustic and trawl data and related to hydrographic parameters as well as to bottom depth. In the central basin, cod were aggregated in an intermediate layer about 15 m thick. This area of peak abundance was defined at its upper limit by the halocline and at the lower limit by oxygen content. The majority of individuals caught in the basin centre were in spawning or pre‐spawning condition with a high proportion of males to females. On the basin slopes, aggregations of cod were found near the bottom. These individuals were mainly immature and maturing stages with an increasing proportion of females to males with size. Salinity and oxygen conditions were found to be the major factors influencing the vertical and horizontal distribution of adult cod. Abundance of immature cod was also positively related to decreasing bottom depths. The effect of temperature was minor. The observed size‐ and sex‐dependent spawning aggregation patterns, in association with habitat volume and stock size, may influence cod catchability and thereby the assessment and exploitation patterns of this stock.
Trans‐oceanic characterization of zooplankton community size structure using an optical plankton counter
Authors: GALLIENNE CHRISTOPHER P. , ROBINS DAVID B.
Published: March 2003

The Atlantic Meridional Transect (AMT), sampling between 50°N and 50°S, is a trans‐oceanic research programme to characterize plankton community structure, productivity and bio‐optical properties of the upper ocean in relation to ocean provinces and meso‐scale features. As part of a suite of continuous measurements, an optical plankton counter (OPC) has been used on the AMT to characterize the surface distribution of zooplankton based on their abundance and community size structure. Results from the OPC were available in real time, and were subsequently validated against microscope counts of zooplankton sampled concurrently along the AMT. Zooplankton community size structure from two sections of the Transect are presented: from the northern edge of upwelling off West Africa to the UK shelf and between the Falkland Islands and Uruguay, where the Transect traversed a warm core ring. Results showing the zooplankton community size structure together with statistical analysis, using principal component analysis (PCA), are compared with the dynamic oceanographic characteristics along the Transect. The application of the OPC for such basin‐scale studies provides a methodology for obtaining data on zooplankton abundance and community structure at the appropriate spatial scales for global‐scale modelling of the marine ecosystem.
Is observed variability in the long‐term results of the Continuous Plankton Recorder survey a response to climate change?
Authors: REID PHILIP C. , PLANQUE BENJAMIN , EDWARDS MARTIN
Published: March 2003

In the more than 50 years that the Continuous Plankton Recorder (CPR) survey has operated on a regular monthly basis in the north‐east Atlantic and North Sea, large changes have been witnessed in the planktonic ecosystem. These changes have taken the form of long‐term trends in abundance for certain species or stepwise changes for others, and in many cases are correlated with a mode of climatic variability in the North Atlantic, either: (1) the North Atlantic Oscillation (NAO), a basin‐scale atmospheric alteration of the pressure field between the Azores high pressure cell and the Icelandic Low; or (2) the Gulf Stream Index (GSI), which measures the latitudinal position of the north wall of the Gulf Stream. Recent work has shown that the changes in the GSI are coupled with the NAO and Pacific Southern Oscillation with a 2 year lag. The plankton variability is also possibly linked to changes observed in the distribution and flux of water masses in the surface, intermediate and deep waters of the North Atlantic. For example, in the last two decades, the extent and location of the formation of North Atlantic Deep Water, Labrador Sea Intermediate Water and Norwegian Sea intermediate and upper‐layer water has altered considerably. This paper discusses the extent to which observed changes in plankton abundance and distribution may be linked to this basin‐scale variability in hydrodynamics. The results are also placed within the context of global climate warming and the possible effects of the observed melting of Arctic permafrost and sea ice on the subpolar North Atlantic.
Interannual variability of the South Georgia marine ecosystem: biological and physical sources of variation in the abundance of krill
Authors: MURPHY E. J. , WATKINS J. L. , REID K. , TRATHAN P. N. , EVERSON I. , CROXALL J. P. , PRIDDLE J. , BRANDON M. A. , BRIERLEY A. S. , HOFMANN E.
Published: March 2003

Interannual variability is a characteristic feature of the Southern Ocean ecosystem, yet the relative roles of biological and physical processes in generating these fluctuations are unknown. There is now extensive evidence that there are years when there is a very low abundance of Antarctic krill (Euphausia superba) in the South Georgia area, and that this variation affects much of the ecosystem, with the most obvious impacts on survival and breeding success of some of the major predators on krill. The open nature of the South Georgia ecosystem means this variability has large‐scale relevance, but even though there are unique time series of data available, information on some key processes is limited. Fluctuations in year‐class success in parts, or all, of the krill population across the Scotia Sea can generate large changes in the available biomass. The ocean transport pathways maintain the large‐scale ecosystem structure by moving krill over large distances to areas where they are available to predator colonies. This large‐scale physical system shows strong spatial and temporal coherence in the patterns of the interannual and subdecadal variability. This physical variability affects both the population dynamics of krill and the transport pathways, emphasizing that both the causes and the consequences of events at South Georgia are part of much larger‐scale processes.
The spring/early summer distribution of Calanus spp. in the northern North Sea and adjacent areas
Authors: Madden H. , Beare D. , Heath M.R. , Fraser J.G. , Gallego A.
Published: March 2003

The spring/early summer distribution of Calanus spp. in the north‐eastern Atlantic and the northern North Sea was studied from data collected on three cruises between 1992 and 1995, and compared against estimates from Continuous Plankton Recorder (CPR) data obtained between 1958 and 1993. The patterns observed in both data sets were examined in relation to the hypothesis proposed by Backhaus et al. (1994) to explain the annual spring invasion of the northern North Sea by Calanus finmarchicus. The results confirmed that arrival of Calanus spp. in the northern North Sea started in March. The main routes of transport into the area were the Norwegian Trench Atlantic Inflow and East Shetland Atlantic Inflow. The highest abundances of Calanus spp. juveniles (stages CI–IV) were found in May in both CPR and cruise data. Although significant differences in absolute abundance of Calanus spp. were found between CPR and cruise data, similar geographical and temporal patterns of spring advection into the North Sea were derived from both data sources, these patterns being consistent with the hypothesized transport mechanisms.
Atlantic menhaden recruitment to a southern estuary: defining potential spawning regions
Authors: Stegmann  , Quinlan  , Werner  , Blanton  , Berrien
Published: March 2003

Atlantic menhaden (Brevoortia tyrannus) is an estuarine‐dependent fish that spawns in coastal waters of the Middle and South Atlantic Bights. Circulation modelling studies of larval transport suggest that recruitment of larvae into the Albemarle‐Pamlico Estuarine System, North Carolina, is linked to dynamics on the shelf from New York to South Carolina. Field‐collected menhaden egg data (from MARMAP and SABRE) define a range of temperatures within which menhaden eggs have been found. In this study we refine the transport model‐predicted spawning grounds for the 1994–95 season by using satellite‐derived sea surface temperature data to highlight regions that are outside the observed spawning temperature range. We also use transport pathways leading from source locations to the estuarine system to characterize the temperature field experienced by particles/larvae during their spawning‐ground to inlet transit. The modelled nearshore location of source regions agrees well with MARMAP and SABRE egg data, and points to the importance of understanding biological and physical linkages between the Middle and South Atlantic Bights. The combination of modelled transport and synoptic temperature maps can provide useful guidance to future sampling efforts as well as help refine our understanding of menhaden ecology.
Coastal sea surface temperature and coho salmon production off the north‐west United States
Authors: Cole James
Published: March 2003

A time series of mean weekly sea surface temperature (SST) images was used to investigate the relationship between fluctuations in the marine survival of hatchery‐reared coho salmon and coastal ocean dynamics off the north‐western United States (51° to 37°N) between 1985 and 1996, using univariate and nonlinear bivariate regression analysis. Ocean conditions were matched against survival for a number of different annual time frames according to the sum of negative or positive weekly SST anomalies. From the univariate analyses, the sum of negative anomalies from April to June, when the juvenile salmon first enter the ocean, was found to have an R2 of 0.88 against survival with 1991 excluded as an outlier. The bivariate multiple regressions used the sum of negative anomalies from April to June as the first independent variable. When the sums of positive anomalies from the following periods during the fishes’ second calendar year in the ocean were each used as the second independent variable, the R2 values were all greater than or equal to 0.92 (with no data points excluded): January to June, February to June, April to June, March to June. These results are discussed within the context of coastal ocean processes. It is concluded that the analysis of SST image time series might allow management to make reasonable forecasts of hatchery‐reared coho salmon survival.
Decadal change in abundance of surface migratory myctophid fishes in the Kuroshio region from 1957 to 1994
Authors: Watanabe Hikaru , Kawaguchi Kouichi
Published: March 2003

Decadal change in abundance of surface migratory myctophid fishes was examined in the Kuroshio region of the western North Pacific for the 35 yr from 1957 to 1994 in relation to the Kuroshio regime shift, indicated by changes in its transport volume and sea surface temperature in the early 1970s. Each year, samples were collected from the 0‐ to 1‐m depth layer at night, from January to March, at 83 stations on average. Ten species belonging to five genera occurred. Juveniles [standard length (SL) ≤ 40 mm] and adults (SL > 40 mm) of each species were analysed. In juveniles, Myctophum asperum, M. nitidulum, Symbolophorus evermanni and Centrobranchus brevirostris accounted for 91.1% of the total catch (7419 individuals), while M. nitidulum contributed 82.4% of the total adult catch (494 individuals). The abundance of juvenile S. evermanni, C. brevirostris and M. nitidulum showed prominent peaks in 1971, together with adult M. nitidulum. These peaks corresponded to extraordinarily high zooplankton abundance in the Kuroshio region in 1971, suggesting high recruitment success and low adult mortality in surface migratory myctophids. Smaller changes in abundance in other years were species‐specific, and the fluctuation patterns were mainly explained by year‐to‐year fluctuations in the strength of the Kuroshio and the geographical distribution of each species, i.e. an increased Kuroshio flow volume resulted in an increase in tropical species and a decrease in temperate species, but no change in the pan‐Kuroshio species.
Intercalibrating SCOR, NORPAC and bongo nets and the consequences for interpreting decadal‐scale variation in zooplankton biomass in the Gulf of Alaska
Authors: Mckinnell S. M. , Mackas D. L.
Published: March 2003

The Canadian weathership time series of zooplankton wet weight biomass, collected at Ocean Station Papa in the Gulf of Alaska from 1956 to 1981, is one of the most comprehensive of its kind in marine science. In 1966, the sampling gear changed from a white North Pacific (NORPAC) net to a black Scientific Committee on Oceanic Research (SCOR) net and it was recently discovered that insufficient intercalibration samples were collected to understand how their sampling properties differed. A Canada‐GLOBEC project to redo the intercalibration of these net types and to understand how they relate to current sampling gear (bongo net) started in 1997. Seventy replicates of the three net types were collected in deep water in the Gulf of Alaska. The major finding is that all nets have similar sampling characteristics, whereas earlier reports indicated that NORPAC biomass values should be multiplied by a factor of 1.538 to be equivalent to the SCOR net. It now appears that this factor arose because flowmeters were not used in the original 1956–81 sampling (volume filtered was estimated from tow length × mouth area). A positive bias was introduced into the SCOR values because relatively more water passed through the SCOR net (undetected without a flow meter) than through the NORPAC net. This means that the unmetered NORPAC samples from 1956 to 1966 should not be adjusted and the unmetered SCOR values should be reduced by a factor that is related to wire angle. The general effect on the entire series is to lower the average biomass estimates, but more so for the early portion of the series than the later years.
The distribution of dippers,Cinclus cinclus(L.), in the acid‐sensitive region of Wales 1984–95
Authors: Buckton  , Brewin  , Lewis  , Stevens  , Ormerod
Published: March 2003

1. Dippers were surveyed along seventy‐four acid‐sensitive streams in upland Wales in 1984 and again in 1995. At forty‐eight of the sites, and in an additional twenty‐three to twenty‐nine adjacent catchments, changes in acid‐base status and macroinvertebrate communities were assessed. River habitat surveys (RHS) and GIS (Geographical Information System) provided information on habitat features.

2. pH means across all the sites were higher on average by 0.12 pH units in 1995 than 1984, accompanied by significantly increased total hardness and reduced sulphate. However, geometric mean aluminium concentrations increased significantly, while the abundances of important dipper prey either remained constant (Ephemeroptera) or declined (Trichoptera; Plecoptera).

3. As in 1984, dipper distribution in 1995 was related to acid‐base status: aluminium concentrations were significantly higher, and pH significantly lower, at sites where dippers were absent. In both surveys, there were significantly more bankside broadleaves and fewer conifers where dippers were present.

4. Although dippers occurred in 1995 on a similar number of streams as in 1984, there were both gains and losses, and an overall significant reduction in the number of visits on which birds were recorded (= registrations) per survey reach. Gains and losses were not related to habitat structure or acid‐base status, and might be stochastic. Mean aluminium concentrations increased more (P < 0.06) at sites where dipper registrations fell, than where they increased, but changes were large enough to explain altered occupancy at only five sites. Plecopteran abundances declined most at sites losing birds.

5. We conclude that recovery from acidification has not yet been large or sustained enough to allow widescale increase in the Welsh dipper population, and continued decline cannot be excluded. There is a need for better understanding of how recovery processes will permeate foodwebs to reach top predators in acidified streams, and of the geographical scale of recovery required to increase populations in dispersed organisms such as birds. Such uncertainties, together with the mismatch in trends revealed by stream chemistry and dippers, illustrate reasons why chemical data alone are inadequate for the assessment of changing river quality.
Mitochondrial DNA polymorphism among alpine populations of Gammarus lacustris (Crustacea, Amphipoda)
Authors: Meyran  , Taberlet
Published: March 2003

1. Mitochondrial DNA sequence analysis was used to investigate the phylogeographic structure among populations of the amphipod Gammarus lacustris isolated in high altitude lakes from the Northern to the Southern Alps, and to investigate the historical and demographic events that may have accompanied this differentiation.

2. The comparison of a 376‐base segment of the mitochondrial cytochrome c oxidase I gene in fifty‐four specimens from nine different populations reveals no variation within populations. However, northern populations appear divergent from those from the Southern Alps. A particular population, located at the limit between the Northern and Southern Alps shows an intermediate haplotype related to the southern lineage.

3. Consideration of the different mitochondrial lineages, together with geographical differences among populations, suggests a scenario for the post‐glacial colonization of G. lacustris in the alpine lakes.
Macroconsumer effects on insect detritivores and detritus processing in a tropical stream
Authors: Rosemond Amy D. , Pringle Catherine M. , Ramírez Alonso
Published: March 2003

1. Few studies have assessed the effects of macroconsumers, such as fishes and shrimps, on detritus and detritivores.

2. We used an underwater electric field to prevent macroconsumers from feeding in and on leaf packs in a lowland stream in Costa Rica and thus to determine their effects on the density of insect detritivores and decay rates of leaves.

3. Exclusion of macroconsumers resulted in significantly higher densities of small invertebrates inhabiting leaf packs. Most of these were collector–gatherers, none were shredders.

4. Despite the increase in invertebrate density, decay rates of leaves were not statistically different. These findings contrast with results from temperate streams showing that increases in the density of invertebrates in leaf packs typically result in an increased rate of decay.

5. Leaf decay rates and invertebrate densities were also compared between leaf packs placed in electric exclusion treatments and those placed in coarse (2 cm) plastic net bags (as used in many previous studies). Our results suggest that using such netting in tropical streams may deter macroconsumers, which can affect insect density and, potentially, decay rates of organic matter.
Effects of eutrophication on seasonal patterns of mesozooplankton in a tropical reservoir: a 4‐year study in Pampulha Lake, Brazil
Authors: Pinto‐coelho Ricardo M.
Published: March 2003

1. Pampulha Lake has undergone rapid eutrophication. Annual maxima of total phosphorus and conductivity increased steadily from 1993 to 1996. Nitrogen quickly decreased after macrophyte removal in 1994, but increased again in the following years

2. The zooplankton was dominated by Daphnia gessneri, D. laevis, Diaphanosoma birgei and Thermocyclops decipiens. The biomass of major zooplankton organisms, including Daphnia and rotifers, increased during the period covered in this study.

3. Autocorrelation coefficients have confirmed the existence of recurrent seasonal patterns for both chemical and biological variables.

4. Daphnia, calanoid copepods and rotifers showed clear and recurrent seasonal patterns. Cyclopoid copepods and Diaphanosoma had temporal patterns more affected by long‐term trophic changes. Other organisms such as Moina, Ceriodaphnia and Bosmina exhibited high temporal variability with no recurrent patterns.

5. There was a strong and positive correlation between total phosphorus and Daphnia biomass. Seasonal patterns of this cladoceran were also inversely associated with sestonic C:P ratios. Thus, Daphnia may be limited primarily by phosphorus and not by total food availability as expressed by particulate carbon.

6. This study suggests that increasing eutrophication has changed the structure as well as seasonal patterns of the zooplankton community in Pampulha Reservoir.
Does body storage act as a food‐availability cue for adaptive adjustment of egg size and number in Daphnia magna?
Authors: Glazier Douglas S.
Published: March 2003

1. The hypothesis that body storage is used by daphniids as a physiological cue for adaptively adjusting egg size and number to food availability was tested.

2. Egg size and number were examined to see whether they are related to individual variation in body storage independent of maternal size, genotype and food level. Egg mass and brood size (number of eggs in a brood) were compared to somatic mass, all adjusted to maternal body length, at two food levels in two parthenogenetic clones of Daphnia magna.

3. The prediction that adjusted brood size should increase with body storage, whereas adjusted egg mass should decrease with increasing body storage, was not fulfilled as seven of eight comparisons failed to fit the expectation.

4. It is concluded that body storage is probably not the food‐availability cue used by daphniids to control intrabrood resource allocation. Other possibilities, such as chemical cues emitted by food organisms and by coexisting cladocerans, are briefly discussed.
Effects of solar radiation on bacterial and fungal density on aquatic plant detritus
Authors: Denward C. M. T. , Edling H. , Tranvik L. J.
Published: March 2003

1. The effects of solar radiation on bacterial and fungal growth on aquatic macrophyte detritus were studied in a microcosm experiment. Senescent leaves of Phragmites australis were incubated for 63 days in shallow water in the shade under photosynthetically active radiation (PAR) together with ultraviolet radiation, or under filters removing either ultraviolet B (UVB) or both UVB and ultraviolet A (UVA).

2. Bacterial abundance and bacterial 3H‐leucine incorporation in the water were measured, together with α‐ and β‐D‐glucosidase activity. In addition, bacterial abundance and fungal biomass associated with the litter were measured.

3. The results indicate that both PAR and UVA affect the micro‐organisms involved in the decomposition of leaf litter. The α/β‐D‐glucosidase activity ratio was less than one in irradiated and more than one in shaded microcosms, suggesting a change in the substrate dissolved organic matter composition towards more β‐ than α‐glycosidic linkages as a result of solar radiation.

4. Microcosms receiving UVB displayed a significantly higher β‐D‐glucosidase activity than shaded microcosms, and those exposed to PAR or PAR + UVA, demonstrating the potential importance of UVB radiation.

5. The free‐living bacteria tended to be dominated by filamentous forms in microcosms subject to solar radiation, especially PAR, and attached microbial communities showed a greater tendency to be dominated by bacteria in irradiated microcosms than in shaded microcosms.
Effects of prey dispersal on predator–prey interactions in streams
Authors: Dahl J. , Greenberg L.
Published: March 2003

1. We studied the effect of mesh size (6 and 3 mm) on interactions between brown trout (Salmo trutta) and benthic invertebrates in enclosures placed in a stream in southern Sweden. We also compared how different prey exchange rates affected interactions between trout and invertebrates.

2. Trout had strong impacts on some benthic taxa, and different mesh sizes produced different patterns. Trout affected the abundance of 10 of the 21 taxa examined, six in enclosures with 3 mm mesh and six in enclosures with 6 mm mesh. The abundance of nine of the prey taxa was lower in the presence of trout, only leptocerids were more numerous in the presence of trout.

3. Our measurements of prey immigration/emigration, together with trout diet data, suggest that direct consumption by trout, rather than avoidance behaviour by prey, explains most decreases in prey abundance. There was avoidance behaviour by only two of the twenty‐one prey taxa, with trout inducing emigration of the mayflies Baetis rhodani and Paraleptophlebia sp.

4. Trout indirectly increased periphyton biomass in both 3 and 6 mm enclosures. The effect of trout on periphyton was probably due to strong effects of trout on the grazer, Baetis rhodani, Heptagenia sp. and Paralepthoplebia sp.

5. Our results suggest that mesh size, through its effects on exchange rates of prey, may affect interactions between predators and prey in running waters, but that the effects of dispersal and predation on invertebrates are taxon specific.
Ecosystem measures of river health and their response to riparian and catchment degradation
Authors: Bunn S. E. , Davies P. M. , Mosisch T. D.
Published: March 2003

1. Measurements of ecological patterns are often used as primary biological indicators of river health. However, these patterns provide little information about important stream ecosystem processes (e.g. the sources and fate of energy and nutrients). The direct measurement of these processes is considered fundamental to the determination of the health of stream and river ecosystems.

2. In this paper we used two basic approaches to assess stream ecosystem response to catchment disturbance and, particularly, to the loss of riparian vegetation in different forested biomes across Australia. Benthic gross primary production (GPP) and respiration (R24) provided measures of the amounts of organic carbon produced and consumed within the system, respectively. Stable isotope analysis was used to trace the fate of terrestrial and instream sources of organic matter in the aquatic food web. In a focal catchment in SE Queensland, additional measurements were taken of riparian attributes, catchment features and water quality.

3. Baseline measurements of GPP and R24 from undisturbed forest streams provided reference values for healthy streams for comparison with sites where the catchment or riparian vegetation had been disturbed. These values of metabolism were low by world standards in all biomes examined. Preliminary data from the Mary River catchment in SE Queensland indicated that these parameters were sensitive to variations in riparian canopy cover and, to a lesser extent, catchment clearing, and predictive models were developed. The ratio P : R (GPP : R24) was used to determine whether sites were net consumers (P < R) or producers (P > R) of carbon but this was not considered a reliable indicator of stream health on its own.

4. Although forest streams were typically net consumers of carbon (P < < R), stable isotope analysis of metazoan food webs indicated a high dependence on inconspicuous epilithic algae in some biomes.

5. A dramatic decline in the health of forest streams was observed when GPP substantially exceeded R24, especially when instream primary producers shifted from palatable unicellular algae to prolific filamentous green algae and macrophytes. These sources of instream production do not appear to enter aquatic food webs, either directly through grazing or indirectly through a detrital loop. Accumulation of these plants has led to changes in channel morphology, loss of aquatic habitat and often a major decline in water quality in some of the streams studied.
Long‐term movements of self‐marked caddisfly larvae (Trichoptera: Sericostomatidae) in a California coastal mountain stream
Authors: Jackson J. K. , Mcelravy E.R.I.C. P. , Resh V.I.ncent H.
Published: March 2003

1. Over 140 000 larvae of the case‐building caddisfly Gumaga nigricula were self‐marked as they incorporated glitter into small portions of their cases while reared in streamside troughs. These marked individuals were released into stream pools and their movements monitored in the dry season, when base flow was low and no spates occurred, and in the wet season when base flow was high and several spates occurred.

2. Of the 9,000–10 000 larvae released in each of two stream pools in the dry season, 4–20% (i.e. 377–1817 marked individuals) were observed on three sampling dates (4, 11 and 24 d after release). Most larvae (87–93%) remained within 4 m up‐ or downstream of the release line after 24 d. No larvae were found outside of the release pools, even after 37 d.

3. Of the > 120 000 larvae released in one stream pool near the beginning of the wet season, 408 larvae were recaptured 130–167 d later, a period that included 30 days of high flow associated with six spates. Estimated survivorship over this period was 0.7–6.2%; there was no relationship between survival and larval size at release. Most (75%) recaptured larvae were found in the pool where they were originally released. The remaining larvae were found downstream of the release pool. Larvae had generally dispersed only a short distance downstream of the release pool (median = 18 m, maximum = 222 m). In addition, four marked pupae were later found 436 m downstream of the release pool.

4. These results illustrate the sedentary nature of larval G. nigricula as well as the important role that high flow events play in larval mortality and dispersal. These case‐building larvae move very little during low flow periods, even when food resources appear limiting. In contrast, the frequency and distance of larval dispersal are much greater during periods with high flow.

5. Our observations for G. nigricula support previously published inferences that larval dispersal within a stream can be limited for some aquatic insects. However, our observations also suggest that, even for a relatively sedentary species like G. nigricula, larval dispersal during periods with high flow may contribute significantly to gene flow within a stream reach.
Changes in the plankton community following introduction of filter‐feeding planktivorous fish
Authors: Fukushima Michio , Takamura Noriko , Sun Liwei , Nakagawa Megumi , Matsushige Kazuo , Xie P.I.N.G.
Published: March 2003

1. We conducted enclosure experiments in a shallow eutrophic lake, in which a biomass gradient of the filter‐feeding planktivore, silver carp, Hypophthalmichthys molitrix Valenciennes, was created, and subsequent community changes in both zooplankton and phytoplankton were examined.

2. During a summer experiment, a bloom of Anabaena flos‐aquae developed (≈ 8000 cells mL−1) solely in an enclosure without silver carp. Concurrent with, or slightly preceding the Anabaena bloom, the number of rotifer species and their abundance increased from seven to twelve species (1700–14 400 organisms L−1) after the bloom in this fish‐free enclosure. Protozoans and bacteria were generally insensitive to the gradient of silver carp biomass.

3. During an autumn experiment, on the other hand, large herbivorous crustaceans were more efficient than silver carp in suppressing the algae, partly because the lower water temperature (≈ 24 °C) inhibited active feeding of this warm‐water fish and also formation of algal colonies. Heterotrophic nanoflagellate and bacterial densities were also influenced negatively by the crustaceans.

4. Correspondence analysis (CA) was applied to the weekly community data of zooplankton and phytoplankton. A major effect detected in the zooplankton community was the presence/absence of silver carp rather than the biomass of silver carp, whereas that in the phytoplankton community was the fish biomass before the Anabaena bloom, but shifted to the presence/absence of the fish after the bloom.
Inhibition of phytoplankton photosynthesis by solar ultraviolet radiation: studies in Lake Titicaca, Bolivia
Authors: Villafae V. E. , Andrade M. , Lairana V. , Zaratti F. , Helbling E. W.
Published: March 2003

1. Lake Titicaca is a large, high altitude (3810 m a.s.l.) tropical lake (16°S, 68°W) that lies on the border of Bolivia and Perú, receiving high fluxes of ultraviolet radiation (UVR) throughout the year. Our studies were conducted during September of 1997 with the main objective of studying the impact of solar UVR upon phytoplankton photosynthesis.

2. Water samples were taken daily and incubated in situ (down to 14 m depth) under three radiation treatments to study the relative responses to PAR (Photosynthetic Available Radiation, 400–700 nm), UV‐A (320–400 nm), and UV‐B (280–320 nm) radiation.

3. Photosynthetic inhibition by UVR in surface waters was about 80%, with UV‐A accounting for 60% and UV‐B for 20%; the inhibition by high levels of PAR was less than 20%. The inhibition due to UVR decreased with depth so that there were no significant differences between treatments at 8.5 m depth.

4. The amount of inhibition per unit energy received by phytoplankton indicates that even though there was a significant inhibition of photosynthesis due to UVR, species in Lake Titicaca seem to be better adapted than species in high latitude environments.

5. The cellular concentration of UV‐absorbing compounds, a possible mechanism of photoadaptation, was low in phytoplanktonic species. However, they were abundant in zooplankton, suggesting a high rate of bioaccumulation through the diet.
The endemic spring snail Pyrgulopsis montezumensis in a high CO2 environment: Importance of extreme chemical habitats as refugia
Authors: O’Brien Chris , Blinn Dean W.
Published: March 2003

1. We examined the distribution of the endemic spring snail, Pyrgulopsis montezumensis, along a gradient of dissolved free CO2 and on selected substrata in the collapsed travertine springmound of Montezuma Well, Arizona, U.S.A.

2. Dissolved CO2 concentration ranged from 480 (SE ± 56) mg L−−1 near the bottom spring vents in the limnetic zone (12 m deep) of the well to < 20 mg L−−1 in an irrigation canal about 1400 m downstream from the well outlet. Spring snails occurred in habitats with 110–315 mg L−−1 dissolved CO2.

3. Laboratory experiments showed that P. montezumensis tolerated a dissolved CO2 concentration up to about 400 mg L−−1 for 11 days, but displayed 40% (SE ± 4) mortality after 3 days at 728 mg L−−1 and 100% mortality after 24 h at 1200 mg L−−1. We also measured 100% mortality after 10 days at ambient concentrations (< 10 mg L−−1) of dissolved CO2.

4. Although the concentration of dissolved CO2 was within the tolerance range for spring snails in the irrigation canal, inadequate substrata and increased predation probably restricted their distribution in the lower reaches of the canal. Both field measurements and laboratory selection experiments showed a significant (P < 0.001) preference for limestone substrata over submerged vegetation and fine sediments.

5. We propose that springs with high dissolved CO2 may provide refugia from invertebrate and/or vertebrate predators not physiologically adjusted to the extreme chemical environment. These extreme chemical habitats probably reduce competition for resources and predation and allow resistant populations like P. montezumensis to attain high density.