bluuebunny/crossref_metadata_2025 huggingface dataset:
Marine temperatures experienced by postsmolts and the survival of Atlantic salmon, Salmo salar L., in the North Sea area
Authors: FRIEDLAND KEVIN D. , HANSEN LARS P. , DUNKLEY DAVID A.
Published: March 2003

The survival of two Atlantic salmon stocks that inhabit rivers confluent with the North Sea was examined in respect to historical distributions of sea surface water temperatures. The rivers Figgjo and North Esk are relatively small salmon rivers in southern Norway and eastern Scotland, respectively. Wild salmon smolts have been tagged in these rivers since 1965. Tag returns were used to evaluate the survival of salmon in the North Sea. Survival rates of one‐sea‐winter (1SW) and 2SW fish were correlated within stocks, as well as between stocks. Survival rates were compared with the areal extent of thermal habitat in the north‐eastern Atlantic Ocean. A positive correlation was found between the area of 8–10°C water in May and the survival of salmon. A reciprocal negative correlation was also found between survival and 5–7°C water in the same month. An analysis of sea surface temperature distributions for periods of good vs. poor salmon survival showed that when cool surface waters dominate the Norwegian coast and North Sea during May, salmon survival has been poor. Conversely, when the 8°C isotherm has extended northward along the Norwegian coast during May, survival has been good. The effect of water temperature distributions on the growth of postsmolts and other survival factors are discussed.
Seasonal changes in respiration rates of copepodite stage V Calanus finmarchicus (Gunnerus)
Authors: Ingvarsdóttir A. , Houlihan D.F. , Heath M.R. , Hay S.J.
Published: March 2003

Copepodite stage V Calanus finmarchicus were collected at locations on the continental shelf north of Scotland, in the Faroe–Shetland Channel and west of Ireland on six occasions covering winter, spring and summer from October 1993 to June 1995. Oxygen consumption by the overwintering and active spring/summer population of animals was determined at temperatures close to in situ temperatures. Laboratory measurements of oxygen consumption were also made at standardized temperatures (0°C, 5°C, 7°C and 12.5°C) to determine the sensitivity of animals to temperature change in the different seasons. Rates of oxygen consumption were very low (7–30 μmol O2 gC−1 h−1) at in situ temperatures during the winter and early spring and significantly higher (105–219 μmol O2 gC−1 h−1) for the active surface population in May and June. Animals collected from the overwintering population showed no significant response to changes in temperature. Due to the low respiration rates, the calculated rate of decrease in carbon content in diapausing copepodite stage CV was very low (approximately 0.250 μgC day−1). The respiration rates were used to construct a model to estimate survival of the animals with an initial carbon content equivalent to that expected of animals in October. The results showed that in order to survive during winter and have enough energy for moulting and migration to the surface in the spring, these animals have to live at temperatures close to 0°C and be in a diapause state.
Spawning and transport dynamics of Atlantic menhaden: inferences from characteristics of immigrating larvae and predictions of a hydrodynamic model
Authors: Rice  , Quinlan  , Nixon  , Hettler Jr  , Warlen  , Stegmann
Published: March 2003

We examined patterns of abundance, age and spawning date distributions of Atlantic menhaden Brevoortia tyrannus larvae immigrating during two seasons through three North Carolina inlets—Oregon, Ocracoke and Beaufort—to elucidate their spawning and transport dynamics. These patterns were examined in conjunction with corresponding predictions from a three‐dimensional, wind‐and tide‐driven hydrodynamic model. Larvae immigrating through different inlets showed consistent similarities as well as marked differences in temporal patterns of abundance, spawning dates and transport times. Intraseasonal patterns in abundance and spawning date distributions among inlets suggest that, in both study years, the spatio‐temporal dynamics of menhaden immigration were driven by large‐scale patterns along the Atlantic coast, rather than by localized variation in spawning activity. Interannual differences in the temporal patterns of spawning dates and larval immigration indicate interannual differences in transport dynamics and/or the spatial‐temporal distribution of spawning. When the spawning locations predicted by the hydrodynamic model are interpreted in conjunction with advanced very high resolution radiometer sea‐surface temperature information, the results are consistent with the limited historical information available on spatio‐temporal distribution of Atlantic menhaden eggs and larvae. The transport model also predicted distributions of arrival times for immigrating larvae that were comparable in range and variability with observed patterns. Our use of data from immigrating larvae, coupled with a hydrodynamic transport model and sea‐surface temperatures, allowed us to uncover relationships between spatio‐temporal patterns of Atlantic menhaden spawning and transport dynamics that could not have been identified by either approach alone.
Interdecadal variations in Japanese sardine and ocean/climate
Authors: YASUDA ICHIRO , SUGISAKI HIROYA , WATANABE YOSHIRO , MINOBE SHO‐SHIRO , OOZEKI YOSHIOKI
Published: March 2003

Relations between the long‐term variations in numbers of Japanese sardine and in ocean/climate were studied. We examined long‐term records of the spring air temperature on the north‐western coast of North America (ATNA; 40–50°N, 130–110°W) reconstructed from tree rings, and the sardine catch records inferred from documents dating from 1600 to 1990. High sardine catches occurred eight times in this period, and each high catch continued for 7–45 years. We found a significant difference in mean ATNAs between the abundant and poor catch periods: high (low) catch occurred in periods of high (low) ATNA. ATNA was negatively correlated with spring sea‐surface temperature east of Japan (SSTJ; 36–40°N, 150–160°E), where the sardine possibly migrate north‐eastward, a relation which was confirmed from 1940 to 1990. In years when the Aleutian Low Pressure System (AL) shifted south‐east and intensified, the westerly wind was strong east of Japan along the south‐western edge of the AL, resulting in low SSTJ; a warm south‐westerly wind blows in the west coast of North America along the south‐eastern edge of the AL. If we assume that this relation between ATNA and SSTJ can be extended back to the 1600s, high (low) catches occur in the period when SSTJ is low (high). This relation between sardine catch and SSTJ is consistent with previous studies based on data from after 1900. The present results suggest that long‐term variations in Japanese sardine are related to interdecadal North Pacific ocean/climate variability.
Assessing the northern diversion of sockeye salmon returning to the Fraser River, BC
Authors: MCKINNELL SKIP , FREELAND HOWARD J. , GROULX SARAH D.
Published: March 2003

We examine the oft‐quoted relationship between the migration of Fraser River sockeye salmon around the northern end of Vancouver Island and sea surface temperatures. We examine the methods used to estimate the northern diversion and conclude that the estimates have a sufficiently low expected error to form a useful representation of sockeye salmon behaviour. The well‐known relationship with Kains Island sea surface temperature is explored and problems are pointed out. In particular, we explore why Kains Island temperatures are good predictors of salmon behaviour in May when the sockeye can be over 1000 km away, but the coastal temperatures are poor predictors in July to September when the salmon are actually close by. We show that a more robust predictor can be developed using open ocean temperature fields and we show why Kains Island fails as a predictor during the summer months. Finally, we show by cross‐validation that the northern diversion is predictable with an r.m.s. error of about 0.1.
Temporal and spatial responses of British Columbia steelhead (Oncorhynchus mykiss) populations to ocean climate shifts
Authors: Welch  , Ward  , Smith  , Eveson
Published: March 2003

The pattern of temporal change in recruitment of steelhead trout (Oncorhynchus mykiss) entering the ocean between 1963 and 1990 was geographically coherent in all regions of British Columbia. A major increase in recruitment was evident for smolts entering the ocean after 1977. Subsequently, an out‐of‐phase response occurred after 1990, indicating that the effect of a possible 1990 regime shift had both temporal and geographical structure. Steelhead entering northern regions had increasing recruitment, while steelhead entering southern BC coastal regions had sharply decreasing recruitment. The evidence clearly indicates that the overall recruitment response since 1977 was primarily shaped by changes in marine (not freshwater) survival. Similar sudden changes in adult recruitment also appear to be occurring for other species of Pacific salmon in BC and Oregon, such as coho (O. kisutch), which appear to occur suddenly and show considerable persistence. A possible explanation for the change is that ocean productivity declined in coastal regions of southern BC after 1990, reducing the marine growth of juvenile salmon. The Bakun upwelling index shows a pattern of geographical coherence along the west coast of North America that could in principle explain the observed pattern of changes in recruitment. However, no evidence for a temporal shift in this index occurring around 1977 and 1990 is apparent. The reason for the sudden and persistent decline in ocean survival is therefore uncertain.
Fluctuations of landings and environmental conditions in the north‐western Mediterranean Sea
Authors: Lloret Josep , Lleonart Jordi , Solé Ignasi , Fromentin Jean‐Marc
Published: March 2003

Most of the monthly catches and CPUE of 13 studied commercial species in the coastal waters of the north‐western Mediterranean were significantly positively correlated with run‐off of local rivers (Rhône and Muga) and the wind mixing index during the spawning season, with time lags of less than a year (transfer function analyses). Rhône and Ebre interannual fluctuations in run‐off were synchronous and were related to the North Atlantic Oscillation (NAO), river run‐offs being negatively correlated to high NAO episodes. The fluctuations of river discharges and the wind mixing index were cyclic but not related. The results showed that enhanced hydroclimatic conditions in the NW Mediterranean were favourable for the productivity of the fish and invertebrate stocks, and suggest the presence of linkage between recruitment of Mediterranean species and local (river discharges, wind conditions) and global (NAO) environmental conditions.
North Pacific Atmospheric and SST Anomalies in 1997: Links to ENSO?
Authors: Overland James E. , Bond Nicholas A. , Adams Jennifer Miletta
Published: March 2003

In the summer of 1997, positive sea surface temperature anomalies (SSTA) extended across the Gulf of Alaska (GOA) and into the eastern Bering Sea (EBS). The SSTA in the EBS are at least in part due to atmospheric causes. Anomalously high 925 mb temperatures and 700 mb geopotential heights and low 925 mb relative humidities, and hence decreased low cloud cover, occurred over the region during April to August. This resulted in enhanced warming of the GOA and EBS owing to increased insolation. The anomalous solar heating was particularly great in the EBS from mid‐May to mid‐July. The pattern of positive 700 mb height anomalies for April to August 1997 is similar to its counterpart formed by compositing the April to August anomalies that occurred during previous El Niños. The positive equatorial SSTA for 1997 was one of the strongest on record for summer months. The existence of an equatorial/high‐latitude connection and the strength of the summer equatorial SSTA in 1997 suggest an El Niño/Southern Oscillation (ENSO) influence in the GOA and EBS. The warming in the Bering Sea and North Pacific during summer 1997 appears to be due in part to the confluence of three meteorological factors which favoured clear skies. There was not only an El Niño influence, but also a decadal trend toward higher 700 mb geopotential heights and a particularly strong blocking ridge weather pattern over the Gulf of Alaska in May.
Habitat associations of Atlantic herring in the Shetland area: influence of spatial scale and geographic segmentation
Authors: Maravelias CHRISTOS D.
Published: March 2003

This study considers the habitat associations of a pelagic species with a range of biotic and abiotic factors at three different spatial scales. Generalized additive models (GAM) are used to analyse trends in the distributional abundance of Atlantic herring (Clupea harengus) in relation to thermocline and water depth, seabed roughness and hardness, sea surface salinity and temperature, zooplankton abundance and spatial location. Two geographical segments of the population, those east and west of the Shetland Islands (northern North Sea, ICES Div IVa), are examined. The differences in the ecological preferences of the species in these two distinct geographical areas are elucidated and the degree that these environmental relationships might be modulated by the change of support of the data is also considered. Part of the observed variability of the pre‐spawning distribution of herring was explained by different parameters in these two regions. Notwithstanding this, key determinants of the species’ spatial aggregation in both areas were zooplankton abundance and the nature of the seabed substrate. The relative importance of the variables examined did not change significantly at different spatial scales of the observation window. The diverse significance of various environmental factors on herring distribution was attributed mainly to the interaction of species’ dynamics with the different characteristics of the ecosystem, east and west of the Shetland Islands. Results suggest that the current 2.5 nautical miles as elementary sampling distance unit (ESDU) is a reasonable sampling scheme that combines the need to reduce the data volume while maintaining spatial resolution to distinguish the species/environment relationships.
Interannual variation in spring biomass and gut content composition of copepods in the Kuroshio current, 1971–89
Authors: Nakata K. , Koyama S. , Matsukawa Y.
Published: March 2003

We examined the effects of climate factors on interannual variations of copepod biomass and gut content composition in early spring in the Kuroshio and the slope water off the Pacific coast of central Japan from 1971 to 1989. The biomass trends were different for large (prosomal length ≥ 1 mm) and small (prosomal length < 1 mm) copepods in both waters. Peaks in biomass of large copepods decreased in magnitude, and the biomass of small copepods was low around 1980. For the large copepods in the Kuroshio, 3‐year running mean biomass was related to the Kuroshio meander index. The yearly mean biomass was related to diatom abundance in the gut which, in turn, was related to wind speed and temperature. The 3‐year running mean biomass of large copepods in the slope water was positively related to solar radiation in March. The biomass of small copepods in both waters was negatively related to solar radiation in February, and years with high biomass of small copepods corresponded with not only the years with high abundance of larger foods (diatoms and micro‐sized foods) in copepod guts, but also with the years with high abundance of the nano‐sized foods. We hypothesize that nutrient supply to upper layers regulates interannual variation of biomass of large copepods in the Kuroshio. Thus, climate influences both size composition and biomass of copepods in and near the Kuroshio in early spring.
Assemblages of vertical migratory mesopelagic fish in the transitional region of the western North Pacific
Authors: Sassa Chiyuki , Kawaguchi Kouichi , Kinoshita Takahiro , Watanabe Chikako
Published: March 2003

Assemblages of vertical migratory mesopelagic fish are described for the nighttime upper 20 m layer of the transitional and adjacent waters in the western North Pacific. Twenty‐three mesopelagic fish species belonging to six families and 16 genera were collected during June 1996. Family Myctophidae was most speciose, represented by 17 species, followed by Sternoptychidae (two spp.) and Bathylagidae (one spp.). Six assemblages are recognized based on their species composition: Subarctic, Northern Transition, Southern Transition, Subtropical, Slope Water and Seamount Assemblages. These assemblages are also characterized by size composition and biomass of the catches. The distributions of the Subarctic, Northern Transition, Southern Transition and Subtropical Assemblages are approximately defined by the Kuroshio and Oyashio fronts and the Subarctic Boundary. Slope Water and Seamount Assemblages are closely related to the slope water around the shelf edge off Japan and waters around the Shatsky Rise and the Emperor Seamount chain, respectively. The importance of the Southern Transition Assemblage area between the Kuroshio front and Subarctic Boundary as spawning and nursery grounds of many subarctic, transitional and subtropical fishes is elucidated, based on the geographical distribution patterns of their larvae and juveniles.
Spatial distribution and overlap between ichthyoplankton and pelagic fish and squids on the southern flank of Georges Bank
Authors: Garrison Lance P. , Michaels William , Link Jason S. , Fogarty Michael J.
Published: March 2003

We conducted larval and adult fish surveys on the southern flank of Georges Bank during the spring of two years (1990 and 1995) with contrasting physical conditions. We employed canonical correspondence analysis (CCA) to examine the relationships between physical variables and the spatial distribution of pelagic fish and ichthyoplankton. Surface temperature bottom temperature, and vertical stratification were significant factors affecting larval fish distributions, and there were groups of species with similar responses to these variables. There were also consistent relationships between physical variables and pelagic fish and squid abundances and spatial distributions. Pelagic fish and ichthyoplankton with similar responses to hydrographic variables had high spatial overlap, and variation in hydrographic regimes modulated the strength of this interaction. Pelagic fish and squids are potentially important predators of both larval and juvenile fish on Georges Bank. Hydrographic structure modulates the degree of spatial overlap and therefore likely influences the strength of predator–prey interactions.
Coexistence of anadromous and lacustrine life histories of the shirauo, Salangichthys microdon
Authors: Arai T. , Hayano H. , Asami H. , Miyazaki N.
Published: March 2003

The environmental history of the shirauo, Salangichthys microdon, was examined in terms of strontium (Sr) and calcium (Ca) uptake in the otolith, by means of wavelength dispersive X‐ray spectrometry on an electron microprobe. Anadromous and lacustrine type of the shirauo were found to occur sympatric. Otolith Sr concentration or Sr : Ca ratios of anadromous shirauo fluctuated strongly along the life‐history transect in accordance with the migration (habitat) pattern from sea to freshwater. In contrast, the Sr concentration or the Sr : Ca ratios of lacustrine shirauo remained at consistently low levels throughout the otolith. The higher ratios in anadromous shirauo, in the otolith region from the core to 90–230 μm, corresponded to the initial sea‐going period, probably reflecting the ambient salinity or the seawater–freshwater gradient in Sr concentration. The findings clearly indicated that otolith Sr : Ca ratios reflected individual life histories, enabling these anadromous shirauo to be distinguished from lacustrine shirauo.
A portable flow chamber forin situdetermination of benthic metabolism
Authors: Dodds W. K. , Brock J.
Published: March 2003

1. Many stream ecologists are interested in determining the metabolic rates of benthic organisms, particularly those of production and respiration. It is often necessary to make these measurements on fresh material in the field at remote sites. Recirculating chambers are commonly used for this purpose.

2. A broad variety of recirculating chambers are described in the literature, but each design has inherent limitations. The most common are inability to control flow in the chamber and match it with external flow rates, and a lack of the power required to do this for extended periods. Alteration of spectral irradiance, temperature rise and elevated internal chamber pressures are additional limitations that have received little attention.

3. We have designed and constructed a flow chamber that eliminates some of these problems. The chamber utilizes a DC motor‐driven propeller as an efficient recirculator (axial impeller), minimizing power requirements and it is constructed of UVB transparent acrylic to allow a full spectral complement of solar irradiance in the interior. Modular components allow the chamber to be taken apart quickly for cleaning and replacement of parts, making it more functional than some previous designs.

4. The axial impeller chamber was compared to a similar sized conventional chamber that had a small diameter return line and a high capacity centrifugal pump. The axial impeller chamber had less of a temperature rise during field incubations, lower power consumption and less internal pressure in the return line when producing equivalent water velocities.

5. The reported axial impeller design had relatively homogeneous velocity across the working section relative to other chambers and was capable of water velocities in excess of 1 m s–1.
Ecology of cryptophytes coexisting near a freshwater chemocline
Authors: Gervais Frank
Published: March 2003

1. A deep chlorophyll maximum dominated by Cryptomonas phaseolus, Cryptomonas undulata and often also by Cryptomonas rostratiformis was observed near the summer chemocline of the dimictic, meso‐eutrophic lake Schlachtensee from 1990 to 1996.

2. The cryptophyte populations occupied a stratified water column of about 2 m thickness just below the oxycline. They were never observed in the summer epilimnion. In their habitat, oxygen concentration was always lower than 1 mg L–1 and light was growth‐limiting, whereas nitrogen and phosphorus were available at high concentrations.

3. A very large portion of the populations stayed in the anaerobic, sulphide‐containing water layer. Below the chemocline, purple and green sulphur bacteria coexisted.

4. The cryptophyte populations were maintained by in situ growth due to low‐light adapted photosynthesis and not due to phagotrophy.

5. Short‐term changes in the light climate near the chemocline could explain the coexistence of different cryptophyte species.
Length–weight relationships of eight freshwater planktonic crustacean species in Japan
Authors: Kawabata Keiichi , Urabe Jotaro
Published: March 2003

1. The relationships between body length and dry weight were examined for eight species of freshwater planktonic crustacea common in Japan: Eodiaptomus japonicus, Acanthodiaptomus pacificus, Daphnia galeata, D. similis, D. magna, Scapholeberis mucronata, Simocephalus exspinosus and Bosmina longirostris.

2. The relationships of two diaptomid species were similar and the approximate equation was lnW = 2.7 + 2.6*lnL, where L is prosome length (mm) and W is dry weight (μg). The carapace length–dry weight relationships in branchiopods were more variable, with the slope ranging from 1.9 to 2.9 and the intercept from 2.0 to 3.7.

3. The effects of food conditions on the relationship were examined in the laboratory, and the seasonal changes in the field were also studied.

4. Practical advice is presented for predicting crustacean weight from body length.
Comparative feeding selectivity of herbivorous insects on water lilies: aquatic vs. semi‐terrestrial insects and submersed vs. floating leaves
Authors: Cronin Greg , Wissing Katherine D. , Lodge David M.
Published: March 2003

1. The rate of grazing damage experienced by submersed and floating leaves of water lilies (Nuphar variegata and Nymphaea odorata) was monitored in lakes in the Upper Peninsula of Michigan, U.S.A. Herbivores damaged 0.2–1.7% of the leaf surface of water lilies per day. These grazing rates differed between plant species, between submersed and floating leaves, and between lakes. Some leaves had more than 60% of their surface damaged and an overall mean of 16% damage occurred during the 2–3 week monitoring period of this study.

2. Snapshot measurements of grazing damage on randomly collected submersed and floating leaves of Nuphar showed that submersed leaves were more damaged (11.0 ± 1.6%, n = 84) than floating leaves (3.8 ± 0.6%, n = 92). Overall, these 176 Nuphar leaves had 7.2% of their area damaged.

3. Five species of herbivorous insects were commonly found on water lilies (Nymphaeacea). One primarily aquatic insect (sensuNewman 1991), a caddisfly larva (Trichoptera: Limniphilidae), had a generalized diet of water lilies, other macrophytes, algae, and detritus. Four of the five insects were from primarily terrestrial insect groups (Coleoptera and Diptera;‘secondary invaders’, sensuNewman 1991) and consumed only water lilies in food preference experiments.

4. The feeding preferences of the generalist trichopteran were altered when the macrophytes were freeze‐dried, ground into a powder, and reconstituted in an alginate gel. This suggests that plant structure may be an important feeding determinant for this insect. In contrast, a specialist weevil preferred its host plant in choice assays, regardless of whether fresh tissue or reconstituted macrophytes were used, suggesting this insect cued on a unique, non‐structural property of its host plant.

5. These results suggest that herbivory on freshwater macrophytes is of a similar magnitude to that on terrestrial plants. The findings of this study are consistent with the hypothesis that herbivorous insects of primarily terrestrial groups have a narrower diet breadth than insects of primarily aquatic groups.
Comparisons of benthic communities adjacent to riparian native eucalypt and introduced willow vegetation
Authors: Read Martin G. , Barmuta LeoN. A.
Published: March 2003

1. Willows, Salix spp., have been widely introduced as a riparian species in temperate Australia and New Zealand. The present study was a broad‐scale observational survey to document the differences between reaches of river lined with willows and native vegetation in the community structure of benthic invertebrates and the resources which these plants use.

2. Nine rivers in south‐eastern Tasmania were examined on three occasions in autumn, spring and summer. Taxa were identified to family level, with the exception of Oligochaeta and Acarina, and benthic organic matter (CPOM and FPOM) and epilithic biomass were measured for each reach.

3. Taxon diversity and evenness were lower in willowed reaches in autumn, and total macroinvertebrate density and number of taxa were lowest in willowed reaches in summer. No differences in the fauna between willowed and native reaches were observed in spring. Measures of community similarity of the fauna in willowed and native reaches were significantly different in autumn and summer, but not in spring.

4. The taxa responsible for the significant differences seemed to be responding to differences in food availability and habitat quality in reaches of each vegetation type. Organic matter standing stock was higher in willowed reaches in autumn although the influence of these litter inputs on the fauna were not marked. Epilithon biomass was highest in autumn and spring in willowed reaches when shading in these reaches was least.

5. The most marked differences between willowed and native reaches were during summer low flows, when the instream fauna appeared to be responding to changes to shading, water quality and the quality of the habitat.
Effects of toxic and non‐toxic cyanobacteria on the life history of tropical and temperate cladocerans
Authors: FerrÃo‐Filho Aloysio S. , Azevedo Sandra M.F.O. , DeMott William R.
Published: March 2003

1. This study compares the effects of four toxic strains of Microcystis aeruginosa on tropical and temperate Cladocera. Survival was tested in acute toxicity experiments using Microcystis alone or in mixtures with the edible green algae Ankistrodesmus falcatus. The effect of chronic exposure on population growth was estimated in life‐table experiments by varying the proportion of Microcystis and the green alga. Nutritional deficiency was assessed using a non‐toxic cyanobacterium in a zooplankton growth experiment. Feeding inhibition was tested using a

C‐labelled green alga as a tracer in mixtures with toxic Microcystis.  2. Toxicity varied consistently between Microcystis strains, while sensitivity varied consistently between cladoceran species. However, no relationship was found between sensitivity and geographical origin or cladoceran body size. Two small‐bodied cladocerans from the same tropical lake, Ceriodaphnia cornuta and Moinodaphnia macleayi, were the least sensitive and most sensitive species, respectively.  3. Surprisingly, two small tropical cladocerans survived longer without food than did three large Daphnia species and a third small tropical species.  4. Each of the three tropical Microcystis strains strongly reduced the population growth rate (little ‘r’) and reproductive output of each cladoceran, this reduction being proportional to the percentage of toxic cells in the diet.  5. As the sole food source, the non‐toxic cyanobacterium, Synechococcus elongatus, supported poor growth in M. macleayi. The nutritional deficiency was overcome when Synechococcus was mixed with either Ankistrodesmus or an emulsion rich in omega‐3 fatty acids.  6. Microcystis inhibited the feeding rate of two cladocerans, even when it comprised only 5% of a mixture with the green algae A. falcatus.  7. Differences in sensitivity to the toxic cyanobacterium appear to be associated with differences in life history between the cladoceran species rather than differences between tropical and temperate taxa. Slow‐growing species that are resistant to starvation appear less sensitive to toxic Microcystis than fast‐growing species, which also tend to die more quickly in the absence of food.
Epilithic algal communities and their relationship to environmental variables in lakes of the English Lake District
Authors: King Lydia , Barker Philip , Jones Roger I.
Published: March 2003

1. The relationship between epilithic algal communities and 17 environmental variables from 17 oligo‐ to eutrophic lakes in the English Lake District was explored using canonical correspondence analysis (CCA). Total phosphorus (TP) and calcium (Ca) concentration were the most important variables accounting for species distribution.  2. Weighted‐averaging regression and calibration models with tolerance downweighting and classical deshrinking were developed to infer TP, Ca, dissolved inorganic carbon (DIC) and conductivity from the relative abundance of 138 epilithic algal taxa.  3. The ranges of the environmental variables covered by the models are 0.8‐49.2 μg L−1 for TP, 2.2–13.0 mg L−1 for Ca, 0.5–8.6 mg L−1 for DIC and 38–124 μS cm−1 for conductivity. Within these limits the models can be used to infer chemical properties of lakes from epilithic communities in the English Lake District.  4. The major advantages of using transfer functions based on epilithic communities are the low logistic requirements and the integrative character of algal samples compared to direct point measurements of chemical parameters of the lakes.
Chironomid stratigraphy in the shallow and eutrophic Lake Søbygaard, Denmark: chironomid–macrophyte co‐occurrence
Authors: Brodersen Klaus Peter , Odgaard Bent V. , Vestergaard Ole , Anderson N. John
Published: March 2003

1. A sediment core from the shallow, hypertrophic Lake Søbygaard (mean depth ∼1 m; [TP] 310 μg P L−1) was analysed for subfossil remains to reconstruct chironomid community changes in relation to the succession and disappearance of aquatic macrophytes.  2. Species composition in the 1.10 m core indicates a succession from a ‘naturally’ eutrophic state to a hypertrophic state during recent centuries. Radiometric dating (210Pb) of the uppermost 20 cm of the sediment core (∼1932–93) indicates that sediment accumulation rate had doubled in recent decades.  3. Changes in chironomid assemblages were in close agreement with changes in both diatoms and macrophyte remains in the same core. Distinct changes in chironomid communities reflect the eutrophication process and macrophyte succession through Chara, Ceratophyllum and Potamogeton dominance to the present state, with complete loss of submerged vegetation and dominance by phytoplankton.  4. The co‐occurrence and relationship between aquatic macrophyte diversity and recent subfossil chironomid assemblages were assessed from an additional 25 Danish lakes. There was good agreement between the macrophyte and chironomid‐based lake groupings. Overall, a significant difference (P<0.001) was found in chironomid assemblages among lakes in different macrophyte classes. In a pair‐wise comparison, the poorly buffered mesotrophic lakes and the alkaline eutrophic lakes had significantly different chironomid assemblages.  5. Chironomid taxa commonly reported to be associated with macrophytes (Cricotopus, Endochironomus and Glyptotendipes) were shown also to be indicators of highly productive lakes lacking abundant submerged vegetation.
The importance of crayfish in the breakdown of rhododendron leaf litter
Authors: Schofield Kate A. , Pringle Catherine M. , Meyer Judy L. , Sutherland Andrew B.
Published: March 2003

1. Rhododendron (Rhododendron maximum) is a common evergreen shrub in riparian areas of the southern Appalachians, where its leaves can comprise a large proportion of leaf litter in streams. However, they are relatively refractory and generally considered a low quality food resource for detritivores.

2. Our objective was to assess whether macroconsumers [primarily crayfish (Cambarus bartonii)] influence rhododendron leaf breakdown in a forested southern Appalachian stream in both summer (when leaves other than rhododendron are relatively scarce) and autumn (when other leaves are relatively abundant). We conducted two leaf decay experiments, one in summer and one in autumn, using pre‐conditioned leaves. Macroconsumers were excluded from the benthos of a fourth‐order stream using electric ‘fences’; we predicted that excluding macroconsumers would reduce the decay rate of rhododendron leaves in both summer and autumn.

3. In both experiments, breakdown rate was lower in exclusion treatments. Macroconsumers accounted for approximately 33 and 54% of rhododendron decay in summer and autumn, respectively. We attribute this effect to direct shredding of rhododendron by crayfish. Biomass of insect shredders, insect predators and fungi did not differ between control and exclusion treatments, indicating that insectivorous sculpins (Cottus bairdi) had no effect on rhododendron decay and that omnivorous crayfish did not exert an indirect effect via alteration of insect or fungal biomass.

4. The influence of shredding insects varied between summer and autumn. In summer, when other, more palatable leaf types were not available, rhododendron leaf packs appeared to provide ‘resource islands’ for insect shredders. There was a significant inverse relationship between insect shredders and leaf pack mass in the summer exclusion treatment: insects were the only organisms eating leaves in this treatment and, as shredder biomass increased, remaining leaf pack mass decreased. In the control treatment, however, we did not see this relationship; here, the effect of insect shredders was presumably swamped by the impact of crayfish. In autumn, when other leaves were abundant, insect shredder biomass in rhododendron leaf packs was less than one‐third of summer values.

5. Even at low density (approximately 2 m–2) crayfish were able to influence an ecosystem process such as leaf decay in both summer and autumn. Given the threatened status of many crayfish species in the United States, this finding is especially relevant. Even small alterations in crayfish assemblages, whether via loss of native species and/or introduction of exotic species, may have significant repercussions for ecosystem function.
Drift dispersal of mayfly nymphs in the presence of chemical and visual cues from diurnal drift‐ and nocturnal benthic‐foraging fishes
Authors: Miyasaka Hitoshi , Nakano Shigeru
Published: March 2003

1. The drift of Baetis thermicus nymphs in the presence of chemical, visual and hydrodynamic cues, considered individually and in combination, produced by different predatory fishes was examined experimentally in laboratory streams. Masu salmon (Oncorhynchus masou) and freshwater sculpin (Cottus nozawae) are typical drift‐ and benthic‐foraging fishes, respectively.

2. Observations of fish swimming in the streams revealed differing diel periodicity between the species; sculpin were nocturnal foragers and salmon diurnal.

3. The drift rate of Baetis by night increased in the presence of chemical cues from sculpin, with other cues having no interactive effects. In contrast, the drift rate increased primarily in the presence of both chemical and, particularly, visual cues from salmon, although no additional effects were found for any non‐visual cues. Visual cues could enable Baetis to assess precisely the predation risk from foraging salmon by day, whereas Baetis could not use visual cues to detect sculpin either at night, because of the low light intensity, or during the day, because of the low activity of sculpin at that time.

4. In natural streams, which are often inhabited by several predatory fish employing different modes of foraging, invertebrates may be able to precisely assess the risk and effectively to avoid predators by using cues unique to each.
Under‐ice blooms and source‐water odour in a nutrient‐poor reservoir: biological, ecological and applied perspectives
Authors: Watson S. B. , Satchwill T. , Dixon E. , Mccauley E.
Published: March 2003

1. Algal taste and odour is usually associated with open water blooms and eutrophic systems. However, some algal species can produce high biomass under ice‐cover, even at low nutrient concentrations, that can impact water quality. This paper describes a winter odour outbreak in oligotrophic Glenmore Reservoir (Calgary, Alberta, Canada), the major algal species, volatile organic compounds (VOCs) and some treatment implications.

2. Using sensory, chemical and microscope analyses, we monitored odour, algal biomass and taxa, bacteria and major nutrients. In a preliminary assessment of the effectiveness of standard water treatment with this type of algal biomass and odour, we used bench‐scale tests and sampled raw water from the Glenmore treatment plant at successive treatment stages.

3. In the winter of 1999–2000 Glenmore ice‐cover was delayed, nutrients were characteristically low (TP < ∼5 μg L–1), but organic carbon and bacteria were higher than in previous years.

4. During this period there was an increase in algal biomass dominated by the mixotrophic chrysoflagellate Dinobryon divergens. Temporal dynamics of this species were inversely correlated with bacteria, and biomass declined following the establishment of ice‐cover, while depth profiles showed the highest abundance at subsurface layers. This suggested that the population outbreak was triggered by high bacteria abundance but depended on a minimum amount of light, consistent with in vitro studies of other mixotrophic chrysophytes.

5. Other non‐bactiverous taxa were also numerous, notably Asterionella formosa, cryptomonads, dinoflagellates and the synurophyte Synura petersenii.

6. Raw water odour was characteristically fishy, mainly caused by the VOCs 2,4,7‐decatrienal, 2,4‐heptadienal and 2,4‐decadienal. Based on algal population and VOC dynamics, these compounds were attributed to Dinobryon. Trace amounts of 2,6‐nonadienal (S. petersenii) and 1,3,5 and 1,3,6‐octatriene (A. formosa) were also detected. It was concluded that 2,4,7‐decatrienal was the major source of the raw water odour.

7. Sensory and microscopic analyses of pre‐ and post‐treatment samples in the treatment plant indicated a complete removal of odour, but only a 30–60% removal of algal biomass and evident rupture of residual algal cells. Laboratory experiments showed that using standard treatment, chlorination rapidly oxidized 2,4,7‐decatrienal and 2,6‐nonadienal but had little effect on 2,4‐hepta‐ and decadienal.
Longitudinal distribution of macroinvertebrates in two glacier‐fed New Zealand rivers
Authors: Milner Alexander M. , Taylor Russell C. , Winterbourn Michael J.
Published: March 2003

1. Environmental variables, benthic algal biomass and macroinvertebrate fauna were examined from September 1999 to January 2000 (austral summer) along two glacier‐fed rivers in South Island, New Zealand.

2. The rivers were characterized by high flow variability, high turbidity and physically disturbed beds. Water temperature ranged from <1 °C near the glacier margin to 10 °C further downstream.

3. Epilithic algal biomass was very low (<0.1 mg m–2) in months characterized by heavy rainfall, but ranged from 1.1 to 14.4 mg m–2 following an extended period with negligible precipitation.

4. Abundance and diversity of invertebrates in both rivers was low. Dominant taxa were Chironomidae (Orthocladiinae, Podonominae, Diamesinae), although mayfly species (Deleatidium: Leptophlebiidae) also occurred at most sites. A species of Eukiefferiella (Orthocladiinae) was collected at all sites and was the most abundant invertebrate close to the glacier margins. No meiofauna were found in either river.

5. Faunal diversity increased at the lowermost stations where species of Plecoptera, Trichoptera, Coleoptera and non‐chironomid Diptera also occurred.

6. The faunas of the two New Zealand rivers conformed to the conceptual model of Milner & Petts (1994) in that taxon richness increased downstream with water temperature. However, invertebrate abundance increased downstream in only one of the two rivers. Also in contrast to the model predictions, Leptophlebiidae and Orthocladiinae, rather than Diamesinae, dominated the fauna at the coldest sites.
Invertebrate drift in a glacial river and its non‐glacial tributary
Authors: Saltveit S. J. , Haug I. , Brittain J. E.
Published: March 2003

1. Invertebrate drift was studied in a glacially fed river and a non‐glacial tributary in western Norway. Samples were taken during two consecutive 24‐h periods in May, July and October 1997. The 3 months are characterized by snowmelt, ice melt and rainfall runoff, respectively. The main glacial river has colder, more turbid water, especially during the period of maximum ice melt during summer.

2. Chironomidae, especially the genus Diamesa, dominated the drift in the main river in May and October, constituting 97 and 99% of total numbers, respectively. Simuliidae, Plecoptera, Ephemeroptera and Trichoptera were the other main components.

3. A comparison of drift and benthos data revealed that the tributary was of little significance for colonization of the main glacial river. Only some additional species in very low numbers were recorded downstream of the confluence.

4. During July significant differences in diel drift pattern of Chironomidae and Simuliidae existed between the glacial and non‐glacial reaches. There was a mid‐day peak independent of discharge in the glacial river, but this peak was not noted in the tributary. Species of the genus Diamesa appear to be adapted for daytime drift, possibly evolved through the absence of predators and competitors that are typical of rhithral systems where nocturnal drift is more usual.
Direct and indirect impact of two common rotifer species (Keratella spp.) on two abundant ciliate species (Urotricha furcata, Balanion planctonicum)
Authors: Weisse Thomas , Frahm Angela
Published: March 2003

1. We investigated the potential competition and feeding impact of the common rotifer species, Keratella cochlearis and K. quadrata, on the abundant prostomatid ciliates, Urotricha furcata and Balanion planctonicum, in laboratory batch culture experiments. All four species have similar feeding preferences, co‐occur in many freshwater environments, and are thus potential competitors for the same algal food.

2. Two small Cryptomonas species served as food for the ciliates and the rotifers in the experiments. Growth rates of each ciliate species were measured when they grew alone and when they were paired with one of the rotifer species.

3. Both rotifer species reduced the growth rate of U. furcata, probably primarily by direct feeding on the ciliates. Growth rate of B. planctonicum was unaffected by K. cochlearis, but was drastically reduced by grazing and/or mechanical interference of K. quadrata.

4. These results suggest niche partitioning of the sympatric ciliates with respect to their rotifer competitors/predators.
Changes in abundance, composition and controls within the plankton of a fertilised arctic lake
Authors: Bettez Neil D. , Rublee Parke A. , O'Brien John , Miller Michael C.
Published: March 2003

1. An oligotrophic arctic lake was fertilised with inorganic nitrogen and phosphorus as (NH4)2 NO3 and H3PO4 for five summers. The loading rate was 1.7–2.5 mmol N m–2 day–1 and 0.136–0.20 mmol P m–2 day–1 which is two to three times the annual loading of lakes in the area. The heterotrophic microzooplankton community was enumerated during the experiment as well as 1 year pre‐ and post‐treatment.

2. The structure of the microplankton community changed from a nutrient limited system, dominated by oligotrich protozoans and small‐particle feeding rotifers, to a system dominated by a succession of peritrich protozoans and predatory rotifers. These peritrich protozoans and predatory rotifers were not present prior to fertilisation and never constituted more than a small fraction of the biomass in other lakes at the research site. The average biomass of the rotifers and protozoans was more than seven and a half times larger by the end of fertilisation than it was initially.

3. Because of the increases in numbers of individuals in these new taxa, the structure of the microbial food web changed. When fertilisation stopped, most parameters returned to prefertilisation levels within 1 year.