bluuebunny/crossref_metadata_2025 huggingface dataset:
Return migration of adult Atlantic salmon, Salmo salar, in relation to water diverted through a power station
Authors: Thorstad E. B. , Økland F. , Johnsen B. O. , Næsje T. F.
Published: March 2003

Abstract
 The migration of Atlantic salmon,
Salmo salar L., returning to the River Suldalslågen, Norway, was studied in relation to redirection of freshwater flow through a power station. The outlet of the power station is situated in the Hylsfjord, a fjord adjacent to the river mouth. Seventy‐two salmon were tagged with acoustic transmitters, released in the outer part of the fjord system and automatically recorded when entering the Hylsfjord or the river. Data were collected during one period when the power station was running and two periods when the power station was closed. The release of water from the power station did not greatly attract the salmon during their return migration. Proportions of salmon entering the river or time from release to entering the river did not differ among salmon tagged in the different periods. The salmon were recorded in the Hylsfjord both when the power station was running and closed and there were no differences in number of times, number of days or hours recorded in the Hylsfjord among salmon tagged in the three periods. The only significant difference found among periods was duration of continuous stays in the inner part of the Hylsfjord. This may indicate a slight attraction to the freshwater release, but the difference seems small (1.8 vs. 0.7 h) compared with the time the fish stayed in the fjord system before entering the river (16–85 days).
Modelling the influence of light, turbulence and ontogeny on ingestion rates in larval cod and herring
Authors: FIKSEN Ø. , UTNE A.C.W. , AKSNES D.L. , EIANE K. , HELVIK J.V. , SUNDBY S.
Published: March 2003

Based on existing models of fish vision and turbulence‐mediated ingestion rates, we develop a model of ingestion rates in larval fish that combines several physical properties of the environment (turbulence, irradiance, light attenuation) and visual characteristics of predators and prey. The model of visual range was calibrated with observed estimates in larval herring (Clupea harengus) and cod (Gadus morhua). The improved visual ability with length of larvae was predicted to be the most sensitive part of the model. Both turbulence and light had strong impacts on the ingestion rate of larval fish. The optimal level of turbulence increased with larval length. Also, due to the exponential decay of light with depth, it was predicted that larvae will have higher ingestion rates near the surface, even at high wind velocities. It is also proposed that larvae (particularly the smallest larvae) should concentrate on larger prey in turbulent environments. We suggest that biophysical models of larval growth and survival in field situations should include these factors to account for environmental effects on growth, survival and recruitment processes in the early life stages.
Annual cycle of epiplanktonic copepods in Canary Island waters
Authors: HERNÁNDEZ‐LEÓN SANTIAGO
Published: March 2003

The species composition of epiplanktonic (0–20 m depth) copepods was studied over an annual cycle at a sampling interval of approximately 10 days at an oceanic station off Tenerife Island (Canary Islands). A taxonomic list of 110 species was obtained but only species represented by more than 300 individuals in the collection of 35 samples were studied. These comprised 23 species from which only 7 species were represented by more than 1000 individuals from all samples combined. Oithona plumifera was the most abundant species; Oithona setigera, Temora stylifera and Clausocalanus arcuicornis were also well represented. Acartia negligens was only observed after the temperature minimum in late winter. By contrast, Lucicutia flavicornis was observed before this temperature minimum. Nannocalanus minor, although numerically important, was represented only by copepodite stages during the period of study. There was great variability in the abundance of the above‐named species, with some indications of higher abundance at about a 28–30 day period, possibly coinciding with the full moon phase. These fluctuations are discussed in relation to the vertical distribution of copepods, lunar phase, the impact of deep scattering layers on epizooplankton and the importance of these fluctuations in the energy flux through planktonic communities in subtropical waters.
Modelling the transport of larval sandeels on the north‐west European shelf
Authors: PROCTOR ROGER , WRIGHT PETER J. , EVERITT ANDREW
Published: March 2003

This study considers the interannual variability in the advection of sandeel (Ammodytes marinus) larvae on the north‐west European shelf. We use recently collated data on spawning location, age of larvae and the time of hatching (between 1955 and 1993) as input to a particle‐tracking model. Utilizing hourly currents from a 39 year run of a two‐dimensional sea circulation model, cohorts of sandeel larvae were represented as a distribution of particles in space and time, and particle drift was calculated for the larval life stage. The final distributions of particles were compared with actual distributions of 0‐group sandeels in the North Sea, as determined from surveys conducted at around the end of the larval phase. Preliminary examination of the data between 1973 and 1993 indicates that differences in predicted drift could explain some of the large interannual variability in 0‐group distributions. This approach may help to improve our understanding of the frequent colonization events that are typical of this species.
Diel vertical migration of myctophid fishes (Family Myctophidae) in the transitional waters of the western North Pacific
Authors: WATANABE HIKARU , MOKU MASATOSHI , KAWAGUCHI KOUICHI , ISHIMARU KIMIE , OHNO AKINORI
Published: March 2003

The diel vertical migration patterns of adult myctophid fishes were determined in the transitional waters of the western North Pacific off Japan, using day–night sampling from 20 to 700 m depths with a commercial otter trawl in the summer of 1995. A total of 12 species belonging to 9 genera were collected. Four patterns were recognized in the diel vertical migration of 11 of the 12 species. (1) Migrants showing clear day–night habitat separation with peak abundance above 200 m at night: Symbolophorus californiensis, Tarletonbeania taylori, Notoscopelus japonicus, Diaphus theta, Ceratoscopelus warmingi, and Diaphus gigas. (2) Semi‐migrants, in which part of the population often remains in the daytime habitat at night. The distribution depths of migratory and nonmigratory individuals do not overlap: Stenobrachius leucopsarus. (3) Passive‐migrants, in which there is no separation of day–night habitats, but the upper limit of daytime distribution depth shifts to a shallower layer at night, probably as the fish follow migratory prey: Lampanyctus jordani. (4) Nonmigrants: Stenobrachius nannochir, Lampanyctus regalis (> 140 mm SL), and Protomyctophum thompsoni. The day–night habitat temperature ranges are also given for the 11 species. No remarkable east–west differences were seen in the vertical migration patterns compared with previous knowledge of eight of these species in the eastern Pacific. The diel migration patterns are newly described for three other species endemic to the western Pacific. The standing stock of myctophids in the study area was conservatively estimated at 18.5 ± 4.7 g m−2 (avg. ± SD).
Effects of water temperature and wind on year‐class success of Tanner crabs in Bristol Bay, Alaska
Authors: Rosenkranz Gregg E. , Tyler Albert V. , Kruse Gordon H.
Published: March 2003

We investigated five a priori hypotheses on factors affecting year‐class success of commercially exploited Tanner crabs, Chionoecetes bairdi, in Bristol Bay, Alaska, through correlation analysis and multiple regression modelling. Estimates of recruitment from Zheng et al.’s (1998; Can. Spec. Publ. Fish. Aquat. Sci. 125:97–105) length‐based analysis of assessment survey and commercial catch data were used to index year‐class strength. This work extends results of an earlier study (Rosenkranz et al., 1998; Alaska Fish. Res. Bull. 5:18–24), which reported positive correlations between Tanner crab year‐class size and north‐east (NE) winds during the spring larval period, by considering the effects of nondirectional wind speed, bottom and surface water temperature, and abundance of the potential predators sockeye salmon (Oncorhynchus nerka) and Pacific cod (Gadus macrocephalus). No relationships were found between year‐class size and mean wind speed or predator abundance, but positive correlations were found with bottom temperatures during gonadal development and egg incubation. Linear regression models with the independent variables NE wind and bottom temperature accounted for about half the variability in the year‐class strength index (r2=0.50 for males, r2=0.48 for females). Anomalously cold bottom temperatures may adversely affect the Tanner crab reproductive cycle, and NE winds may promote coastal upwelling while advecting larvae to regions of fine sediments favourable for survival upon settling. The role of Bering Sea oceanography on decadal‐scale variability in Tanner crab population dynamics could not be resolved with the relatively short (∼ two decades) time series of stock assessments.
Seal predation on salmon and forage fish schools as a function of tidal currents in the San Juan Islands, Washington, USA
Authors: Zamon Jeannette E.
Published: March 2003

Tidal patterns in feeding behaviour are known in several upper trophic level predators. Although harbour seal (Phoca vitulina richardsi) movements between resting and foraging areas are often correlated with tidal phase, little is known about tidal influences on seal foraging because it is difficult to make direct observations of predation events. This study sought to determine whether harbour seals exhibit tidal patterns in their at‐sea distribution, abundance, and foraging success and to discuss how changes in capture rates or prey types might affect the ability of an individual to meet its daily energy requirement. During 1995–97, seal abundance in the water during flooding tides was significantly greater than median daily abundance. Seals aggregated near a channel constriction. Salmon accounted for 50% and 87% of observed captures of single, large fish in 1996 and 1997, respectively. Predation on schooling fishes involved juvenile sandlance or herring. Large‐fish captures were episodic (16.9% and 27.5% of observations with nonzero capture rates) and occurred more often on the incoming tide near constricted water flow. Median per capita capture rates were highest in currents during slower flooding (0.31 fish·seal–1 h–1). Surface attacks on forage fish schools were more common than large‐fish captures (54.0% and 66.7% of observations with at least one attack on forage fish). Night‐time and subsurface feeding were not assessed. Given what is known about seal food requirements, tidal differences in capture rates are predicted to have a significant impact on both the hunting strategy and energy intake of individuals. Results support the idea that interactions among tidal currents, topographic features, and fish play a role in structuring marine predator–prey dynamics.
Hydrographic phenomena influencing early life stages of the Sicilian Channel anchovy
Authors: Lafuente J. García , García A. , Mazzola S. , Quintanilla L. , Delgado J. , Cuttita A. , Patti B.
Published: March 2003

The information collected from a European Union funded project on the ‘Distribution Biology and Biomass Estimates of the Sicilian Channel Anchovy (Engraulis encrasicolus)’ was used to analyse the linkage between the general circulation pattern of the Atlantic Ionian Stream (AIS) and the reproductive strategy of the Sicilian Channel anchovy. The main spawning ground is located in the NW region of the southern Sicilian coast. This region is a stable area of low current produced by the impingement towards the coast of the AIS and its bifurcation into two branches. The main branch heads towards the SE end of the Sicilian coast (Cape Passero) acting as a transport mechanism for the anchovy eggs and larvae. Along the AIS trajectory, there is a density front to the left of the current, facing downstream. This front is a consequence of the shoreward sloping of isopycnals that maintains the geostrophic flow, facilitating the mixing of deeper waters with surface layers and fertilization of coastal waters. The front enhances primary production assuring food availability for anchovy larvae during their advection by the AIS. The highest concentrations of larval anchovy were found off the SE Sicilian coast, in the area off Cape Passero. The greater average sizes of larvae found in this region, and their estimated age, support the evidence of advection by the AIS. The hydrographic features observed in this area, such as the existence of a well‐defined cyclonic vortex, implies the existence of upwelling in its centre, providing a suitable environment for sustained enhanced rates of primary production and allowing the larval population to maintain their relative position. This retention area is conceived as favourable for providing the necessary feeding conditions. The data acquired from a survey carried out to evaluate the anchovy recruitment strength confirm that larvae reach the juvenile stage in the south‐eastern coast of Sicily, since most of the young‐of‐the‐year anchovy were located in the Cape Passero region.
`Ocean triads' in the Mediterranean Sea: physical mechanisms potentially structuring reproductive habitat suitability (with example application to European anchovy, Engraulis encrasicolus)
Authors: Agostini Vers N. , Bakun Andrew
Published: March 2003

Summaries of maritime weather reports and mean seasonal satellite‐sensed ocean colour distributions for the Mediterranean Sea are used to identify characteristic configurations of physical mechanisms promoting (i) nutrient enrichment, (ii) concentration of larval food distributions, and (iii) local retention of eggs and larvae. Five subbasin scale `ocean triads', hypothesized to be particularly favourable groupings, are identified in the Aegean Sea, the Gulf of Lions and nearby Catalan Coast, the Alboran Sea, the Straits of Sicily/Tunisian Coast, and the Adriatic Sea. These are examined in relation to available knowledge of anchovy spawning grounds. All areas are characterized by patterns of linked wind‐driven Ekman upwelling and downwelling. All areas except the Straits of Sicily are found to have inputs of less saline surface waters offering raised nutrient concentrations, enhanced upper layer stability, and frontal density contrasts, and to have areas where the characteristic rate of turbulent mixing energy input by the wind fall below a reference intensity level. All areas, except the Sicilian Channel/Tunisian Coast, also contain abundant locally reproducing anchovy populations.
Modelling the temperature mediation of growth in larval fish
Authors: Bartsch Joachim
Published: March 2003

A brief description of the logistic growth curve and its derivative is given. It is shown how to incorporate a temperature‐dependent function into this curve without changing the essential mathematical properties. This is accomplished by changing the exponential parameter in the logistic formulation from a constant value to a temperature‐dependent variable. This growth formulation is used to model mackerel (Scomber scombrus) larval growth in a Bio‐Physical Transport Model developed within the EU SEAMAR (Shelf‐Edge Advection, Mortality and Recruitment) project.
Long‐term changes in zooplankton and its relationship with squid, Todarodes pacificus, catch in Japan/East Sea
Authors: Kang Young S. , Kim Jin Y. , Kim Hak G. , Park Jong H.
Published: March 2003

Long‐term change in zooplankton biomass and composition of major zooplankton assemblages was studied with a focus on climate change and squid catch in the Japan/East Sea. This study deals with data sets of zooplankton biomass, abundance of major zooplankton assemblages, and sea surface temperature (SST) obtained during the period from 1965 to 1998, and the catch of squid, Todarodes pacificus, from 1978 to 1998. Based on its physical characteristics, the study area was divided into two subregions, a northern and southern region.

The SST during the winter and spring (February and April) steadily increased after the late 1980s in the southern region. On the other hand, the northern region did not have a warm winter and had higher interannual fluctuations. Zooplankton biomass also showed an increasing trend and major zooplankton assemblages have shifted in their composition since the early 1990s. The northern region exhibited a greater increasing trend than the southern region in zooplankton biomass. Macrozooplankton such as chaethognaths, euphausiids and amphipods gradually increased after the early 1990s. In the Japan/East Sea, squid catches increased continuously after the early 1990s. The squid catch for the autumn of year n is significantly associated with the zooplankton biomass collected in October and December of year n − 1 (r=0.864 in the northern region and r=0.818 in the southern region, P < 0.001) and macrozooplankton, especially euphausiids (r=0.578 in the northern region and r=0.840 in the southern region, P < 0.05) and amphipods (r=0.695 in the northern region and r=0.648 in the southern region, P < 0.05).
Transport of larval jack mackerel (Trachurus japonicus) estimated from trajectories of satellite‐tracked drifters and advective velocity fields obtained from sequential satellite thermal images in the eastern East China Sea
Authors: Kim Hee‐Yong , Sugimoto Takashige
Published: March 2003

Transport processes of jack mackerel (Trachurus japonicus) larvae in the waters off the west coast of Kyushu in the eastern East China Sea, have been investigated using satellite‐tracked surface drifters and consecutive satellite thermal images. Trajectories of drifters describe northward flows over the continental shelf, eastward flows of the Kuroshio south‐west of Kyushu, and a weak clockwise gyre off the west coast of Kyushu. In particular, the clockwise gyre causes the entrainment of jack mackerel larvae into the waters off the west coast of Kyushu. Consecutive satellite thermal images help to elucidate the northward warm water intrusion from the Kuroshio front south‐west of Kyushu. Particle trajectories using sea surface current fields computed with the Maximum Cross Correlation (MCC) technique also reveal that the transport of jack mackerel larvae into the nursery ground off the west coast of Kyushu caused by the anti‐cyclonic gyre and the warm streamers are an important process for successful recruitment.
A spatially explicit study of prey–predator interactions in larval fish: assessing the influence of food and predator abundance on larval growth and survival
Authors: Pepin P. , Dower J. F. , Davidson F. J. M.
Published: March 2003

We apply a coupled biophysical model to reconstruct the environmental history of larval radiated shanny in Conception Bay, Newfoundland. Data on the larvae, their prey and predators were collected during a 2‐week period. Our goal was to determine whether environmentally explicit information could be used to infer the characteristics of individual larvae that are most likely to survive. Backward drift reconstruction was used to assess the influence of variations in the feeding environment on changes in the growth rates of individual larvae. Forward drift projections were used to assess the impact of predators on mortality rates as well as the cumulative density distribution of growth rates in the population of larvae in different areas of the bay. There was relatively little influence of current feeding conditions on increment widths. Patterns of selective mortality indicate that fast‐growing individuals suffered higher mortality rates, suggesting they were growing into a predator's prey field. However, the mortality rates appeared to increase with decreasing predator abundance, based on the drift reconstructions. The relationship of growth and mortality with environmental conditions suggests that short‐term, small‐scale variations in environmental history may be difficult to describe accurately in this relatively small system (∼1000 km2).
Changes in the distribution of sardine eggs and larvae off Portugal, 1985–2000
Authors: Stratoudakis Y. , Bernal M. , Borchers D. L. , Borges M. F.
Published: March 2003

Generalized additive models (GAMs) were fitted to sardine (Sardina pilchardus) egg distribution data from three daily egg production method surveys. The results showed that the area of egg cover off Portugal decreased significantly from 11 800 km2 in 1988 to 7000 km2 in 1997 and 7400 km2 in 1999. This is because of a significant reduction in sardine egg presence off northern Portugal, GAM estimated areas being similar or higher in the late 1990s for southwestern and southern Portugal. The distributional area covered by larvae was not estimated for 1988 (larval distribution extended beyond the survey area), although it was probably higher than the 9600 km2 for 1997 and 5500 km2 for 1999. In 1997 and 1999, the Gulf of Cadiz was also sampled, indicating extensive areas with sardine eggs and larvae (more than 50% of the total area of distribution off Portugal). Standardized data from 15 ichthyoplankton surveys between 1985 and 2000 show a decline in the mean probability of egg presence within the Portuguese continental shelf from the mid‐1980s to the late‐1990s, because of a marked reduction in egg presence off northern Portugal. Sardine larval data from the same surveys suggest that the reduction in mean probability of presence in the north is less marked than for eggs (although this comparison ignores the presence of sardine larvae beyond the continental shelf in the 1980s). Similar changes off northern Portugal and western Galicia are observed in commercial sardine catches and the acoustically estimated area of fish distribution. It is possible that the observed decline in spawning area off northwestern Iberia during the 1990s is indirectly reflecting the prevalence of environmental conditions detrimental to sardine recruitment (northerly winds during winter that favour coastal upwelling and offshore transport), which have reduced the spawning contribution of young fish in that area.
Small‐sized invertebrates in a gravel stream: community structure and variability of benthic rotifers
Authors: Schmid‐Araya J. M.
Published: March 2003

1. The Rotifera assemblage inhabiting the streambed surface and the hyporheic zone of a gravel stream was investigated between October 1991 and October 1992. Forty‐two species of Monogononta and 27 of Bdelloidea were identified. Within these two classes, dominant species differed between the surface and the hyporheic zone. At the streambed surface, the abundance of monogonont rotifers showed a seasonal pattern with significantly higher densities in pools, whereas bdelloids showed no clear temporal trend and did not differ significantly among sites. In the hyporheic zone, the depth distribution differed among the two rotifer groups, bdelloids occurred in highest densities between 0 and 30 cm sediment depth, while monogononts were most abundant at greater depths.

2. Species composition differed greatly between successive sampling dates (min. 5 to max. 26 days) at both the streambed surface and the hyporheos. At the streambed surface and in the shallow hyporheos a significantly higher percentage of species was replaced in riffles than in pools.

3. Few measured hydrophysical variables were associated with the Rotifera assemblage structure. At the streambed surface, species richness was negatively correlated with water temperature and substratum heterogeneity, and Monogononta rotifer densities declined with water depth and substratum roughness.

4. Permutation tests carried out on temporal serial correlations showed that, at riffle sites at the streambed surface, bdelloid rotifer densities, rotifer species richness and diversity did not differ significantly from a temporal, near‐random pattern. The hyporheic rotifer assemblage followed similar near‐random patterns.
Environmental gradients and the horizontal distribution of microcrustaceans in lakes
Authors: Smiley Elizabeth A. , Tessier Alan J.
Published: March 2003

1. The assemblage of suspension‐feeding microcrustaceans in lakes changes along a habitat gradient from nearshore to offshore. This gradient of microcrustaceans was explored in relation to differences in macrophytes and the associated changes in water chemistry, food resources and types of predators.

2. Some microcrustacean species were littoral or limnetic specialists, while others changed their distribution along this horizontal habitat gradient on a diel or seasonal basis. Distribution patterns were similar in a lake and a pond which differed in extent of macrophyte habitat.

3. There was a large shift in the composition of sestonic food, indicating heterotrophic seston nearshore and more autotrophic seston offshore. Sit‐and‐wait predators of microcrustaceans (e.g. Enallagma spp.) dominated nearshore and cruising predators (e.g. Leptodora kindtii Focke) were more common offshore.

4. A reciprocal transplant experiment revealed that littoral specialists could survive equally well when fed littoral or limnetic seston, while limnetic specialists performed poorly when fed littoral seston. Food resources may be important in determining where some microcrustacean species live along this horizontal habitat gradient.
Logistic regression as a tool for defining habitat requirements of two common gammarids
Authors: Peeters Edwin T. H. M. , Gardeniers And Jean J. P.
Published: March 2003

1. Logistic regression predicts the probability of occurrence of a species as a function of environmental variables. This technique was applied to a large data set describing the distribution of two common gammarid species, Gammarus fossarum and G. pulex, in streams in the Netherlands, to evaluate its usefulness in defining habitat requirements.

2. A method is presented that derives optimum habitat ranges for environmental variables from logistic regression equations. The calculated optimum habitat ranges, which are related to the maximum likelihood of presence in the field, agreed with habitat requirements and ecological tolerances in the literature.

3. Single logistic regressions provide good descriptions of the optimum habitat requirements and multiple logistic regressions give insight into the relative importance of each environmental variable. It is the combination that makes logistic regression a valuable tool for constructing habitat suitability indices.

4. Current velocity, pH, Kjeldahl nitrogen, total phosphorus, ammonium nitrogen, conductivity, width and depth are, in this sequence, the most important environmental variables in predicting the probability of occurrence of G. fossarum, whereas current velocity, Kjeldahl nitrogen, pH and depth are the most important variables for the prediction of the probability of occurrence of G. pulex.
The trophic interactions of young Arctic grayling (Thymallus arcticus) in an Arctic tundra stream
Authors: Golden Heidi E. , Deegan And Linda A.
Published: March 2003

1. Young (0+) Arctic grayling (Thymallus arcticus) have the potential to control the trophic structure of Arctic tundra streams through consumption, nutrient excretion and the modification of prey behaviour. The effect of young grayling on three trophic levels (algae, invertebrates and fish) was investigated by manipulating fish density and by fertilizing the river with phosphorus (P).

2. Nutrients, epilithic chlorophyll a, benthic invertebrates and fish biomass were measured within each fish density treatment (0, 4, and 40 fish m–2) within the P‐limited reference zone and the P‐enriched fertilized zone of the Kuparuk River, Alaska.

3. Epilithic chlorophyll a increased with increased fish density in both reference and fertilized zones, while mayfly density decreased with increased fish density in the fertilized zone only. Final mean mass of young grayling in the 40 fish m–2 cages was lower than mean mass in the 4 fish m–2 cages.

4. Young grayling may produce a top‐down cascading trophic effect in areas where nutrients are not limited.

5. River nutrient status and river discharge may modify the strength of top‐down control by young grayling.
How does the vertical distribution of chlorophyll vary in littoral sediments of small lakes?
Authors: Cyr Hélène
Published: March 2003

1. In this study, sediment chlorophyll profiles at twenty littoral stations in three oligo‐mesotrophic lakes were compared to test whether the vertical distribution of chlorophyll is related to site characteristics (light availability, temperature, physical disturbances) and whether these profiles differ between shallow and deep portions of the littoral zone.

2. The magnitude of chlorophyll peaks at the sediment surface did not vary with light intensity. Chlorophyll peaks in the shallow littoral zone had a weak tendency to decrease with increasing effective fetch. The magnitude of chlorophyll peaks at deeper sites was more closely related to water temperature than to substrate slope.

3. High chlorophyll concentrations were measured down to 1–3 cm in the sediments, both at shallow (< 2.5 m) and deep (4–10 m) stations. The depth to which high chlorophyll was found in sediments did not vary with effective fetch or sediment water content, two indices of wave disturbance in the shallow littoral zone, or with substrate slope, an index of sediment stability in the deep littoral zone. Sediment mixing is apparently not related to common indices of physical disturbances.

4. Between 8 and 100% of sediment surface chlorophyll was ‘retained’ 4–5 cm into the sediments. The proportion of chlorophyll ‘retained’ in littoral sediments increased with increasing depth, increasing lake productivity (total phosphorus concentration) and increasing lake pH.

5. Among‐core variability (standard error/mean) in chlorophyll concentration at the sediment surface ranged from less than 1% to 33% at different stations and was highest at shallow, exposed sites. These levels of variability are similar to those found in other periphytic communities.
The relationship between egg size and embryonic and larval development in the freshwater shrimp Paratya australiensis Kemp (Decapoda: Atyidae)
Authors: Hancock Marty A.
Published: March 2003

1. Paratya australiensis egg and clutch sizes vary between lower and upper altitude sites within headwater streams of the Conondale Range, Queensland, Australia. The adaptive significance of this variation is examined by comparing the development of large eggs from upper sites with small eggs from lower sites at ambient temperatures in the laboratory.

2. Embryonic duration was not dependent on egg size, but was a function of temperature (28 days at 18 °C, but only 22 days at 21 °C). However, larvae developing from large eggs were significantly larger at all stages of development, larval duration was shorter and growth rate was faster than that of larvae from small eggs.

3. It is suggested that the larger, more rapidly developing larvae at upper altitude sites have a greater chance of maintaining position within headwater sections of the stream. This is important as physical barriers such as waterfalls may severely restrict upstream movement. At lower altitude sites, maintaining position may not be as critical as there are no major barriers to upstream movement following downstream displacement. The influence of temperature may also be important as larger eggs may be an adaptation to compensate for slower development of eggs and larvae at cooler, upper altitude sites. The advantage in completing larval development quickly is that larvae would have less risk of removal by spates occurring late in the breeding season.
Inhibition of phosphatase activity by dissolved humic substances and hydrolytic reactivation by natural ultraviolet light
Authors: Boavida M. ‐J. , Wetzel R. G.
Published: March 2003

1. Phosphatases released extracellularly by aquatic micro‐organisms often complex with humic compounds that are released from decomposing tissues of plants and imported in dissolved and colloidal forms to lakes and rivers.

2. Dissolved humic substances from several natural sources formed complexes with phosphatases of bacterial and algal origin and reduced hydrolytic activity by non‐competitive inhibition. Restoration of the hydrolytic enzyme activities from the humic substances–enzyme complexes increased progressively over time when exposed experimentally to natural and artificial ultraviolet (UV) irradiance.

3. Greater phosphatase restoration occurred from humic acid–phosphatase complexes when humic acids were extracted from dissolved organic matter (DOM) of mixed natural plant sources, than when humic acids were isolated from a decomposing single plant species.

4. The data support a previously suggested hypothesis that phosphatases and other enzymes in aquatic ecosystems can complex with humic substances that dominate the DOM pool. These humic substances–enzyme complexes, in which the enzyme is temporarily inactivated, can be transported with water movements and displaced to other sites within the ecosystem. Upon exposure to UV irradiance in the photic zone, functional enzymes can be released. The potential for inactivation and storage of enzyme activity, relocation within the ecosystem, and subsequent reactivation holds important implications for regulation of nutrient cycling in fresh waters.
Effects of temperature and ultraviolet radiation on microbial foodweb structure: potential responses to global change
Authors: Rae Rowena , Vincent Warwick F.
Published: March 2003

1. A series of growth experiments were conducted with natural plankton communities from a lake and river in northern Quebec, to evaluate the response of microbial foodweb structure to changes in ambient temperature and solar ultraviolet radiation (UVR).

2. Bioassays were incubated for 6 days at two temperatures (10 and 20 °C) and three near‐surface irradiance conditions [photosynthetically active radiation (PAR) + UVA + UVB, PAR + UVA, and PAR only).

3. The concentration of total bacteria showed no net response to temperature, but the percentage of actively respiring bacteria, as measured with the cellular redox probe

5‐cyano‐2,3‐ditolyl tetrazolium chloride (CTC), was up to 57% higher at 20 °C relative to 10 °C. Chlorophyll a concentrations in the < 2 μm size fraction also reacted strongly to temperature, with a net increase of up to 61% over the temperature range of 10–20 °C.

4. The UVR effects were small or undetectable for most of the measured variables; however, the percentage of actively respiring bacteria was significantly inhibited in the presence of UVR at 20 °C, decreasing by 29–48% on day 6 in the lake experiments and by 59% on day 2 in one river experiment.

5. The results show differential sensitivity to temperature among organisms of microbial communities in subarctic freshwaters, and a resilience by the majority of micro‐organisms to their present UVR conditions. Microbial foodwebs in northern freshwaters appear to be relatively unresponsive to short‐term (days) changes in UVR. However, the observed responses to temperature suggest that climate change could influence community structure, with warmer temperatures favouring picoplanktonic phototrophs and heterotrophs, and a shift in nanoplankton species composition and size structure.
Comparative energetics and life cycle of the opossum shrimp (Mysis relicta) in native and non‐native environments
Authors: Chess Dale W. , Stanford Jack A.
Published: March 2003

1. Life history, fecundity and energy ingestion were compared for non‐native Mysis relicta in Flathead Lake, Montana, and in Waterton Lake, Montana/Alberta, where the mysid is native.

2. Based on estimates from stomach contents, M. relicta in Flathead Lake consumed three to four times more energy per hour while foraging than M. relicta from Waterton Lake. The primary prey of M. relicta in Flathead Lake was Daphnia thorata. Diaptomus sicilis was the primary prey for M. relicta in Waterton Lake.

3. Mysis relicta in Flathead Lake had a 1‐year life history. It took 2 years for M. relicta in Waterton Lake to complete a generation. Mysis relicta from Flathead Lake produced significantly (P < 0.05) more eggs per female (19.9 ± 4.7) compared to M. relicta in Waterton Lake (13.7 ± 3.6). The lipid content in eggs from M. relicta in Flathead Lake was also significantly (P < 0.05) higher than eggs from M. relicta in Waterton Lake.

4. In Flathead Lake, M. relicta is able effectively to exploit Daphnia thorata, consuming greater biomass than M. relicta in Waterton Lake. Mysis relicta efficiently assimilates the greater biomass, which reduces generation time, increases fecundity, and increases lipid reserves of offspring. These results provide evidence of energetic mechanisms that enable M. relicta to colonize and affect foodwebs when introduced into lakes.
Restoration and management of riparian ecosystems: a catchment perspective
Authors: Wissmar Robert C. , Beschta Robert L.
Published: March 2003

1. We propose that strategies for the management of riparian ecosystems should incorporate concepts of landscape ecology and contemporary principles of restoration and conservation. A detailed understanding of the temporal and spatial dynamics of the catchment landscape (e.g. changes in the connectivity and functions of channel, riparian and terrestrial components) is critical.

2. This perspective is based upon previous definitions of riparian ecosystems, consideration of functional attributes at different spatial scales and retrospective analyses of anthropogenic influences on river catchments.

3. Restoration strategies must derive from a concise definition of the processes to be restored and conserved, recognition of social values and commitments, quantification of ecological circumstances and the quality of background information and determination of alternatives.

4. The basic components of an effective restoration project include: clear objectives (ecological and physical), baseline data and historical information (e.g. the hydrogeomorphic setting and the disturbance regime), a project design that recognizes functional attributes of biotic refugia, a comparison of plans and outcomes with reference ecosystems; a commitment to long‐term planning, implementation and monitoring and, finally, a willingness to learn from both successes and failures.

5. Particularly important is a thorough understanding of past natural disturbances and human‐induced changes on riparian functions and attributes, obtained by a historical reconstruction of the catchment.
State of environment indicators of ‘river health’: exploring the metaphor
Authors: Fairweather Peter G.
Published: March 2003

1. Indicators are crucial to many socio‐political schemes for portraying environmental influences of society. For example, the OECD model for State of the Environment Reporting uses three different sorts of indicators (pressure, condition, response) to differentiate the present condition of the environment from the anthropogenic pressures upon it and from any societal responses made to alleviate those pressures (thereby improving aspects of the overall condition).

2. These sorts of indicators have a fundamental technical basis in the science supporting their exposition and usage. However, the criteria used in interpreting the indicator values are likely to be set by considerations that go beyond scientific grounds. That is, indicators are socially determined in the end. However, many scientists find it difficult to involve the public in such reporting.

3. Scientists who are uncomfortable with this non‐technical use of their indicator constructs should recognize that it is merely another manifestation of the overall broadening of environmental concern termed ‘ecosystem health’. The emerging field of ecosystem health seeks to take our technical understanding of how the environment functions and combine it with socio‐economic goals, using a human health metaphor and an ethical underpinning.

4. River health might be better served by adopting a veterinary approach rather than the model of human health. This is because, like animals, riverine environments come in many different forms and cannot complain of ill health. Desirable interventions will vary with the uses to which we wish to put a river and our reasons for being concerned about a river’s health. A framework for this diagnostic approach is presented.

5. An enormous challenge lies ahead in integrating the various measurements of riverine attributes that might together constitute ‘river health’. We need ways to cater for the pluralism of modern societies, and we need more dynamic assessments of river condition, possibly founded on studies of key ecological processes.
New generation water quality guidelines for ecosystem protection
Authors: Hart Barry T. , Maher Bill , Lawrence Ian
Published: March 2003

1. Water quality guidelines are important for the management of water resources. Initially, guidelines focused on quality for domestic drinking water and for agricultural, recreational and industrial purposes. More recently, the emphasis has been on ecosystem protection, as well.

2. This paper discusses the key elements of new risk‐based water quality guidelines being developed in Australia and New Zealand, that should lead to more effective management and protection of aquatic ecosystems.

3. There are three essential elements to this new approach: (i) it is ecosystem‐based— ideally the guidelines should be, as far as possible, ecosystem‐specific; (ii) it is issue‐based— the guidelines should focus on the actual issues or problems caused by physical, chemical and biological stressors rather than on the individual indicators, as at present; and (iii) it is risk‐based. There is generally great difficulty in deciding whether adverse biological effects will result from various stressors added to an ecosystem. The new approach develops guideline ‘packages’ for each issue and, where possible, for each ecosystem type. Each ‘package’ consists of specified key performance indicators, trigger levels for these indicators (that is, levels which indicate the degree of risk that adverse biological effects may occur), and for high risk situations (where trigger levels are exceeded) a protocol for considering the effect of ecosystem‐specific factors in reducing (or enhancing) the biological effects.

4. This paper presents a case study related to a highly relevant aquatic ecosystem issue in Australia, namely the excessive growth of cyanobacteria (blue‐green algal blooms), to illustrate how the new risk‐based guidelines might be applied.
The pathway to noxious cyanobacteria blooms in lakes: the food web as the final turn
Authors: Elser James J.
Published: March 2003

1. Cyanobacteria blooms have long been the focus of limnological research as they often represent the ‘end member’ of limnological deterioration under various human impacts. Research over the past several decades has greatly illuminated the ecological factors promoting cyanobacteria blooms but controversy and confusion surround the successful integration of this diverse body of work.

2. In this opinion article I attempt to integrate well‐known aspects of cyanobacteria bloom ecology (such as the roles of nutrient loading, N:P ratio, and mixing conditions) with more recent developments that highlight the importance of feedbacks within the food web in regulating cyanobacteria blooms. Food‐web feedbacks involving stoichiometric mechanisms appear to be particularly important, as accumulating data indicate that the food web influences cyanobacteria not just by regulating the rate of grazing mortality. Rather, trophic interactions may also regulate cyanobacteria dynamics by altering the consumer‐driven nutrient recycling regime in a way that shifts the competitive advantage away from cyanobacteria.

3. Viewed in this way, cyanobacteria blooms can be seen as probabilistic events that are the end result of a series of key mechanisms involving nutrient loading, physical mixing conditions, and trophic interactions. To successfully manage lake water quality we should take advantage of each node of contingency leading to undesirable blooms. In doing so we will also have a more coherent scientific message to communicate with those directly involved with the socioeconomic politics of water quality decision making.
The ecological organisation of lake districts: general introduction
Authors: Kratz Timothy K. , Frost Thomas M.
Published: March 2003

1. Here we introduce a special issue of Freshwater Biology that focuses on the landscape‐scale spatial and temporal patterns exhibited by multiple lakes within lake districts. We call this patterning, and the processes that lead to it, the ‘ecological organisation of lake districts.’

2. Papers in this special issue share the common goal of examining landscape‐level processes that lead to spatial and temporal patterns of lake characteristics in individual or multiple lake districts. Several papers focus on the degree to which multiple lakes have synchronous among year variability in various physical, chemical, and biological variables. Others focus on the landscape‐level processes that lead to spatial patterning of lake characteristics. Finally, a few papers examine the relationship between spatial patterning and temporal dynamics. Papers in this special issue present results from 10 lake districts from North America, Europe, and Antarctica.
The relationship of egg size and incubation temperature to embryonic development time in univoltine and multivoltine aquatic insects
Authors: Gillooly James F. , Dodson Stanley I.
Published: March 2003

1. We used published data to investigate the combined influence of egg size and incubation temperature on embryonic development time for a broad assortment of aquatic insects at four different incubation temperatures (10, 15, 20 and 25 °C).  2. Embryonic development time (EDT) was positively correlated with egg size at each of the four temperatures, but with different relationships for univoltine and multivoltine aquatic insects. The relationships of embryonic development time to egg size expressed in degree‐days did not significantly differ in slope (P>0.50) or intercept (P>0.05) for either univoltine or multivoltine aquatic insects at each of the four temperatures.  3. The relationship of embryonic development time (degree‐days) to egg mass in multivoltine aquatic insects (EDT=885×0.19, P<0.0001, r2=0.48) is similar in slope and intercept to that for other oviparous animals (i.e., zooplankton, fish, amphibians and reptiles), and to the relationship of embryonic development time to neonate mass in mammals. Univoltine species on average require 3–5 times longer to develop (EDT=14190×0.29, P<0.001, r2=0.29) than most other animals of equivalent egg mass, but the relationship of embryonic development time to egg mass is similar in slope to that of most other animals. Together, these relationships provide a basis for evaluating differences in embryonic development time among aquatic insects.