Invertebrate drift in the regulated River Tees, and an unregulated tributary Maize Beck, below Cow Green dam

SUMMARY. The Cow Green dam was completed in the summer of 1970 and invertebrate drift was sampled below the dam and in an adjacent tributary, Maize Beck, on thirty-one occasions between July 1970 and September 1973. Drift was sampled by pumping river water through a filter. The intake was placed in Maize Beck for the first sample and in the Tees for the second, and so on alternately for the rest of the sampling period. Nets were used on ten occasions, nine of these in winter months and once when the pump broke down. A total of ninety-five taxa were recognized, of which eighty-six occurred in Maize Beck and seventy-one in the Tees. The Tees fauna was dominated numerically and in terms of biomass by a large population of micro-crustaceans originating in the reservoir. Hydra and Naididae also formed a large proportion of the Tees drift but contributed little to the biomass. Ephemeroptera were most abundant in Maize Beck samples. Diptera were abundant in drift catches in both streams with simuliid larvae most numerous in Maize Beck and chironomid larvae most numerous in the Tees. The greatest drift densities of the benthic fauna were observed between April and October; the mean number of organisms per 10 m³ were seventy-three in Maize Beck and 144 in the Tees. The mean densities in winter were very low, respectively two and seventeen per 10 m³ in the two rivers. There was no significant difference between the mean levels of the total bottom fauna (numbers and biomass) in the drift in the two rivers during the period April-October, but vrtnter biomass was significantly greater in the Tees. In July 1970 micro-crustaceans represented 29% (14 per 10 m³) of total drift numbers and 3% (0.7 mg wet-weight per 10 m³) of the biomass, whereas in 1973 they represented 99% of both the numbers (37 670 per 10 m³) and weight (2.2 g wet-weight per 10 m³). The relation between benthos and drift was examined. In the drift Plecoptera and Baetidae were more abundant in Maize Beck than in the Tees. Only Chironomidae and Nais spp. were more abundant in the Tees, In the benthos the density of Plecoptera and Baetidae was not significantly different in the two rivers, but all other groups with the exception of Simuliidae occurred at greater densities in the Tees. The proportion of baetids present in the drift was greatest in Maize Beck. No such difference was demonstrated for total fauna. Diel rhythms were observed in baetids and simuhids with densities greater in night catches. Nocturnal peaks of these organisms were less pronounced in the Tees. Chironomid larvae showed no diel changes in abundance. Significant diel changes in the mean weights of individual animals were not detected in baetid nymphs or chironomids. Micro-crustaceans showed no nocturnal peaks of abundance. Preliminary observations on the quality and quantity of seston caught in drift samples between April and October showed great differences between the rivers. In the Tees the bulk ofeach sample consisted of algal filaments derived from the river and micro-crustaceans from the reservoir. In Maize Beck algae were un-common and the sample was composed of peat and mineral particles. Data are presented on seston output at different discharges.     

Features of the structure and spatial distribution of plankton in the Sheksna Reservoir

Based on the field studies conducted in August 2005 and 2007, the distributions of zooplankton structure and abundance, as well as chlorophyll content, in the Sheksna Reservoir are analyzed. A total of 107 zooplankton species have been found (46 Cladocera, 18 Copepoda, and 43 Rotifera), including 24 species (10 Cladocera, 2 Copepoda, and 12 Rotifera) new for the reservoir. In the surface layer of water, where blue-green algae concentrate, zooplankton abundance and biomass are 1.5–5 times lower and the zooplankton structure is simpler than in deeper layers. The highest zooplankton biomass (>3 g/m³) are observed in Lake Beloe and the upper area of the Sheksna section, while in the near-shore sites it did not exceed 1 g/m³. There are no significant changes in zooplankton abundance when compared to the abundance recorded at the end of the past century.     

Seasonal succession of Copepoda in the Bahía Blanca estuary

The abundance and species composition of Copepoda with respect to other mesozooplanktonic groups were studied at the harbour of Ingeniero White in the inner zone of the Bahfa Blanca estuary, between July 1990 and August 1991. Maximal copepod abundances of 4.7 × 10 m^–3 and 4.9 × 10 m^–3 were observed in January 1991 and May 1991, respectively. Minimal abundances of 6 m^–3 were found in June 1990. Acartia tonsa was present throughout the year with high dominance in summer-autumn (December to May). Eurytemora affinis was present from July to October 1990 (first pulse) and from July to September 1991 (second pulse). Euterpina acutifrons was most abundant during spring 1990, whereas Paracalanus parvus was most abundant during winter-spring (July–October) 1990 and April–May 1991. The rest of the copepods were observed during winter and spring 1990 and July–August 1991. Calanoides carinatus and Labidocera fluviatilis, both species from the outer estuarine waters, were only found on two sampling dates. The proportion of meroplanktonic forms was high in certain months of the annual period considered. Differences between the copepod seasonal succession studied here and those observed during several years in the 1980's are discussed.     

Earthworm numbers,biomass and respiratory metabolism in a beech woodland-Wytham Woods,Oxford

Summary The mean annual population density of earthworms was found to be 164.6 m^-2 during a period of detailed study between October 1971 and September 1972. In a year of less detailed study between November 1972 and October 1973 the population density was 117.5 m^-2 (139.8 m^-2 when the type of extraction method was allowed for). Mean biomass densities in the two years of investigation were 41.0 g preserved wet wt m^-2 (1971–1972) and 38.6 (possibly 39.2) g preserved wet wt m^-2 (1972–1973).Comparison of the Brogden's Belt population and biomass densities with those reported from other woodlands indicates that soil type is more important than leaf litter type in determining the numerical abundance of earthworms. Population densities are lower in beechwoods on mor soils, mor soils also support significantly fewer species. As with numbers, mean biomass density in beechwoods on mor soils was significantly lower than that occurring in beechwoods on mull soils; the latter, in turn, being lower than those found in mixed deciduous woods on mull soils. Unlike population density biomass density is influenced by both soil and litter type, this is discussed by reference to mean body weights and food quality as reflected by tannin, nitrogen and carbohydrate content.The annual respiratory metabolism of the Brogden's Belt earthworms was calculated to be between 10.7 and 13.41 O₂ m^-2 a^-1, which is equivalent to between 4.1 and 5.1% of the total soil metabolism. A production/biomass ratio of 0.49–0.58 was estimated, as was a net population efficiency of 22%.     

A Seasonal Quantitative Study of the Littoral Cladocera and Copepoda in a Bog Pond and an Acid Marsh in Newfoundland

A quantitative study was made of the littoral microcrustaceans in a bog pond and an acid marsh located on the Avalon Peninsula, Newfoundland, from May, 1972 to May, 1973. A total of 17 species of Cladocera and 7 species of Copepoda were found in La Manche Marsh, while 21 species of Cladocera and 5 species of Copepoda were collected in Round Pond. The maximum standing stocks were similar in the two localities. The dominant forms in the summer and fall in La Manche Marsh were Cladocera: Acantholeberis curvirostris, Biapertura intermedia, Chydorus sphaericus, and Ilyocryptus spinifer. In the winter the copepod, Macrocyclops albidus, was dominant, while Cyclops varicans rubellus was the most abundant species in the spring. Round Pond also was dominated by Cladocera in the summer and fall; namely, Acroperus alonoides, Alona rustica, Alonella excisa, Chydorus sphaericus, and Sida crystallina. The copepods, Eucyclops agilis and Macrocyclops albidus, were dominant in the winter and early spring.     

A quantitative study of the invertebrate fauna of the River Tees below Cow Green Reservoir

Monthly samples were taken in the River Tees below Cow Green dam from four sites differing in flow conditions, by means of trays containing stones from the river, which were immersed for a period of 1 month. Information on the distribution, abundance and biomass of the benthos of the River Tees is given with additional data on the life-histories of some of the more common species, during the period May 1971 to May 1972. Of the seventy-two taxa found, fourteen made up 95% of the total numbers. Hydra, Polycentropodidae, and the molluscs Limnaea peregra and Ancylus fluviatilis were the most abundant animals in the slower-flowing water (10–26 cm s^?1) and Simuliidae, Orthocladiinae, and Baetis rhodani dominate the riffle (50–75 cm s^?1) fauna numerically. Some organisms, Nais spp., Caenis rivulorum and Baetis scambus favoured intermediate flows of 20–60 cm s^?1. The slowest-flowing water contained the largest number of taxa and the site with the fastest flow supported the least. A mean monthly weight per square metre of 14·56 g (95% limits from 7 to 31) was calculated using data from all four sites. The frequency distribution of nymphal size-classes is given for B. scambus, C. rivulorum, Ephemerella ignita, and Brachycentrus subnubilus, and the association of certain nymphal size-classes with a particular site is analysed. The composition and distribution of the fauna is discussed. It is suggested that the relative richness of the fauna in terms of biomass is attributable to the organic enrichment of the river following the building of the Cow Green dam. The regulation of the flow has allowed the dense growth of algae and mosses, and the development of large molluscan populations, and the reservoir itself provides a rich source of food, particularly zooplankton and phytoplankton, for the river benthos.     

Seasonal fluctuation in the zooplankton community of Azibo reservoir (Portugal)

The seasonal fluctuation in the zooplankton community of Azibo reservoir (Portugal), was studied from November 1986 till November 1987.Fifty-three species of Protozoa, Rotifera, Copepoda and Cladocera were found. The zooplankton community was numerically dominated by rotifers, which represented 66% of the total.The highest rotifer density was reached in the beginning of spring. It decreased after the cladocerans peaked in May.Copepods had two maxima, one in April and another one in September.Although protozoans rose to high densities during winter (1.07 × 10⁵ ind m^–3), their contribution to total biomass was small (2.03%).     

Plankton studies in a lacustrine environment

Summary Weekly zooplankton samples were taken during the period February, 1972 to January, 1973 at station III in a shallow and turbulent tropical reservoir (Broa Reservoir, São Carlos, São Paulo, State-Brazil). The samples were taken by plankton standard net with 68 mesh size, and collected through the horizontal hawls during 3 min. Rotifera was the most abundant group with 77.6%; Cladocera 13.6%, and Copepoda 8.7% (adult and naupliae stages). Other forms like Chaoborus larvae and some worms occurred sporadically. The seasonal fluctuation of the total zooplankton was very irregular in warm and rainy season and more stable in the dry and cold season. The composition of the zooplankton and its patterns of seasonal variation for eutrophic and oligotrophic aquatic ecosystems, in tropical regions, may differ significantly from temperate waters.     

Zooplankton assemblages in two reservoirs: one subjected to accentuated water level fluctuations,the other with more stable water levels

The abundance, composition and dynamics of zooplankton were followed in two reservoirs of the River Douro catchment. The Serra Serrada Reservoir is subject to marked fluctuations in water levels. The highest values of total phosphorus, soluble reactive phosphorus, nitrate, water colour and chlorophyll a were found during the minimum level phase. Rotifera was dominant except in late summer and autumn when the cladoceran Ceriodaphnia quadrangula or the copepod Tropocyclops prasinus replaced them as the dominant zooplankton. Among the rotifers the most common taxa were Keratella cochlearis, Conochilus sp. and Asplanchna priodonta. Maximum rotifer density was about 80,000 ind m⁻³ in 2000, 200,000 ind m⁻³ in 2001 and 100,000 ind m⁻³ in 2002. Among the crustacean zooplankton C. quadrangula achieved densities of up to 45,000 ind m⁻³ and T. prasinus, up to 80,000 ind m⁻³. Canonical correspondence analysis revealed a strong contribution of the variation in the stored water volume, temperature, total phosphorus, chlorophyll, nitrates, and water transparency to the observed, significant association between zooplankton assemblage and environmental variables. In the Azibo Reservoir, fluctuations in water level are smaller. Only total phosphorus, cholorophyll and conductivity varied seasonally. Cladocera and Copepoda were dominant during the whole study period. The most abundant taxa were Ceriodaphnia pulchella, Daphnia longispina, Diaphanosoma brachyurum, Bosmina longirostris and Copidodiaptomus numidicus. Cladocera achieved densities of up to 25,000 ind m⁻³ and Copepoda up to 15,000 ind m⁻³. Rotifera in general reached densities of up to 6,000 ind m⁻³. On the basis of canonical correspondence analysis only temperature and conductivity were significantly associated with zooplankton assemblage.     

Development of the macro-invertebrate fauna of Cow Green reservoir (Upper Teesdale) in the first five years of its existence

SUMMARY. The development of marginal (shore-line), sub-littoral (3–6 m) and profundal (15–18 m) fauna was followed using timed collections in shallow water and artificial substrata in deeper regions. The reservoir started filling in July 1970 and was close to top water level in the autumn of that year. Samples in the marginal zone contained drowned terrestrial organisms and some Cladocera (Chydoridae) in February 1971 but by October, Chironomidae and Oligochaeta became abundant and micro-crustaceans (copepods and cladocerans) formed about 98% of the total catch. Peak densities of micro-crustaceans in the marginal zone were reached in the summer of 1971, but chironomids and oligochaetes were most abundant in the second year after filling. The numbers of marginal zone animals were greatest at the most sheltered site, and lowest at a site on the windward shore. At a stream mouth the rheophilic fauna present in April 1971 was replaced with limnophilic organisms (Chironomidae and Tubificidae) by September 1971. In the sub-littoral, Hydra, Enchytraeidae, Orthocladiinae Tanytarsini and oribatoid mites were the most abundant taxa, whereas Naididae, Hirudinea, Ostracoda, Gammarus pulex, Chironomini and Pisidium spp. were numerous in the profundal zone. Total faunal numbers and biomass were greatest in the profundal zone in all years. The highest annual mean estimate of biomass in the sub-littoral was 3.07 g (wet wt)m^?2 in the second year after filling, thereafter both numbers and biomass fell. In the profundal the maximum biomass (about 29 gm^?2) was observed in the third and fourth years after filling. An estimate of total standing crop of benthic organisms below the drawdown limit, made in July 1974, gave a figure of about 43 tonnes, wet weight. Biomass estimates at Cow Green were compared with those in eighteen other reservoirs and were found to be high especially in relation to those from other upland areas.     

A survey of stream invertebrates in the Cow Green basin (Upper Teesdale) before inundation

In 1967 a programme was initiated by the Freshwater Biological Association to study fish populations within the proposed Cow Green reservoir basin and in the Tees downstream of the dam, before and after impoundment. This paper describes the result of a supporting study on aquatic invertebrates covering the pre-impoundment period 1967–70. The benthic faunas of six streams in the reservoir basin, the Tees below Cauldron Snout and Maize Beck, a tributary ofthe Tees below the dam, were studied. Species list are presented for each habitat and changes in seasonal and annual abundance are discussed. All areas sampled lie at altitudes between 440 and 550 m O.D. and are situated amongst moorland and limestone grassland. Conditions in the streams ranged from slow-flowing peaty reaches to small streams with moss-covered bottoms and larger stony rivers and streams with relatively unstable bottoms. Samples were taken in riffles and pools using the ‘kick’ method wherever possible. An attempt was made to quantify kick-sample catches by comparing them with shovel-sample catches which cover a known area of stream bottom. It was found that 10 5 kicks gave a catch equivalent to the populations of 1 m², giving a population density of about 1200 animals/m for the reservoir-basin riffles. Over 120 taxa were recorded, 100 of which were at the species level. In the reservoir-basin streams, 116 taxa were found with seventy-one in Maize Beck and fifty-six in the Tees below Cauldron Snout. Ephemeroptera were the most abundant group in the reservoir basin and Maize Beck faunas with Rhithrogena semicohrata, Heptagenia lateralis and Baetidae being the most abundant forms, although Ecdyonurus spp. especially E. dispar were much more common in Maize Beck. In other groups Leuctra spp. and Gammarus pulex were very common. In the Tees below Cauldron Snout Limnaea peregra, Chironomidae and Baetidae formed the bulk of the fauna and Plecoptera were uncommon. Amongst the reservoir basin streams Weelhead Sike supported the largest number of species and species groups (eighty-one), and all the streams had forty-nine or more taxa represented. Information on seasonal changes in the numbers of those species or species groups composing 90% or more of the total fauna is presented. Faunal density was high in May with Ephemeroptera, particularly Ecdyonuridae, and the plecopteran Leuctra inermis being the most abundant forms. In August, the numbers of animals appeared t o fall and common members of the community were Baetidae, Diptera, Leuctra fusca and Ecdyonuridae. In October, Ecdyonuridae particularly R. semicolorata, were most abundant. A comparison ofthe bottom fauna of riffles and pools was made and more animals were found in riffles than in pools. The effect of gravel extraction on the bottom fauna of the Tees was examined. A severe drop in the numbers of animals was observed after extraction. Diptera were the first group to return to their pre-disturbance density. Elminthidae and Annelida were worst affected and slowest to recover. The fauna of the area is discussed and possible reasons for its relative species richness are put forward. Habitat diversity and chemical richness appear to be the most likely reasons for the relatively large number of species found.     

Composition and abundance of phytoplankton in the Baidarata Inlet of the Kara Sea in summer and autumn

The species composition and abundance of phytoplankton were determined in the Baidarata Inlet (Kara Sea) in August 2005 and July and September–October 2007. A total number of 220 species were found. In the surface layer, phytoplankton biomass ranged from 1.5 to 15.4 mg C/m³ (mean 5.7 ± 3.0 mg C/m³) in July, from 1.2 to 11.8 mg C/m3 (mean 5.2 ± 2.8 mg C/m³) in August, and from 4.4 to 22.6 mg C/m³ (mean 12.8 ± 5.6 mg C/m³) in September-October. In July at different sampling sites, the biomass was dominated by dinoflagellates, diatoms, and chrysophycean. Dinoflagellates dominated at almost all stations in August. Diatoms dominated in autumn with the most abundant species Paralia sulcata.     

Recovery of copepod, but not cladoceran, zooplankton from severe and chronic effects of multiple stressors

In the mid‐twentieth century, many lakes near Sudbury, Canada, were severely contaminated by acid and metal emissions from local smelters. For example, in the early 1970s, Middle Lake had pH of 4.2, and Cu and Ni levels both >0.5 mg L^?1 . To determine if crustacean zooplankton could recover from such severe and chronic damage, Middle Lake was neutralized in 1973. A comparison of its zooplankton with that of 22 reference (pH > 6) lakes indicates that the planktonic Copepoda completely recovered by 2001. In contrast, the cladoceran assemblage improved but did not recover. Colonist sources existed – Cladocera and Copepoda occurred with equal frequency in area lakes – but six separate colonizations by cladoceran species failed. We argue that local factors, metal toxicity and predation by yellow perch, have, to date, prevented cladoceran recovery. Nonetheless, the complete copepod recovery is encouraging, given the severity and duration of pre‐neutralization stress.     

Invertebrate drift in a large, braided New Zealand river

1. The spatio-temporal patterns of drifting macroinvertebrates in a large, braided New Zealand river were determined by sampling with drift nets, seasonally, for 1 year. 2. Drift densities were greatest in autumn, and at night in all seasons except winter. A greater proportion of larger animals drifted at night than during the day in all seasons. Mean annual drift densities were ninety-six animals 100m^?3 and 47 mg dry weight 100 m^?3. 3. There were relatively few taxa in the drift, and the mayfly Deleatidium spp. comprised more than 85% of the drifting aquatic invertebrates in all seasons except autumn. Chironomidae and terrestrial forms were the only other groups to occur at densities of more than one animal 100 m^?3 in all seasons. 4. Drift density was positively correlated with benthic density, which in turn was adversely affected by floods, particularly during spring and summer.     

Ixodes scapularis Say on white-tailed deer (Odocoileus virginianus) from Long Point, Ontario.

Ixodes scapularis Say was the only species of tick found on white-tailed deer, Odocoileus virginianus, collected at Long Point, Ontario from October 1972 to August 1973. Adults were most abundant from September 1972 to April 1973. Larvae were found throughout the study period except during February. Nymphs were scarce during winter months but fairly common during spring and summer. Most adults were found on the neck and shoulders. Larvae occurred mainly on lower regions of the body and nymphs mainly on the head, shoulders, forelegs and brisket.     

Zooplankton dynamic of Lake Prespa (Macedonia)

The composition and temporal abundance patterns of zooplankton community in Lake Prespa pelagic zone were studied throughout an annual cycle (October 2008–September 2009). Eighteen species (10 Rotifera, 5 Cladocera, 2 Copepoda, 1 Mollusca) were evidenced. It includes Arctodiaptomus steindachneri, an endemic calanoid of the Western Balkans. The zooplankton density varied during the investigated period and certain seasonal successions in temporal transpositions of their maximal development were noticed. The total zooplankton density was much higher in spring and summer period. The representatives of subclass Copepoda were dominant during the whole year. The dominant species was A. steindachneri. At the second place (with exception of the winter period) were the Cladocera representatives. The dominant species was Daphnia cucullata. At the third and fourth place were rotifers and larval form of Dreissena polymorpha, respectively. The quantitative presence of the Copepoda representatives was significantly lower in terms of the previous investigations. The Cladocera quantity reached high values during this period, particularly in summer. Such altering in the quantitative ratio between Copepoda and Cladocera in favor of the Cladocera, especially high quantitative presence of D. cucullata, typical for eutrophic lakes, imply of significant changes in zooplankton community and changes of the water quality in Lake Prespa pelagial.     

Island biogeography, diversity and dominance of zooplankton in crater lakes on the Azores

In July and August 1988 samples of zooplankton were collected from 17 lakes on four islands. Five species of Cladocera, three species of Copepoda and 30 species of Rotifera were found. The maximum numbers of species in any one lake were four planktonic Cladocera, two Copepoda and seven planktonic Rotifera (with up to six additional non-planktonic species). The smallest, most distant island had fewer species than the largest island nearest to the mainland, but the number of species in each lake was determined more by the size of the lake than by its location. This results in the most distant island having lakes containing the same number of species as lakes of similar size on islands nearer to the mainland. The numbers of zooplankton species in each of these lakes are significantly lower than the world average, and the dominance ratios are significantly higher.     

Alteration in the zooplankton community of a fly ash treated lake

The zooplankton community in Lake Charles East, Indiana, was sampled from June, 1974 through September, 1977 as part of a lake restoration study. About 1.8 × 10⁴ kg of lime and 1.8 × 10⁶ kg of ponded fly ash were added to the lake during May through August, 1975 to precipitate phosphate and seal the sediments. Annual mean species number (5.2–11.3) and annual mean species diversity (H′, 0.9–1.3) were highest in 1976, the first year after treatment. By the second post-treatment year these variables had returned to pretreatment levels. Prior to treatment Cladocera were dominant during fall and early winter (Sept.–Dec. 1974), with Copepoda dominant in late winter and spring (Jan.–May 1975). After treatment Cladocera were dominant throughout the fall and winter (Nov. 1957–May 1976). Copepoda were again dominant in August 1976. The short term effect of the treatment appeared to be termination of the latter part of the copepod annual cycle through elimination of aestivating copepodites in the summer and increased abundance of Cladocera during the winter and spring immediately following treatment. Community composition one year after treatment was similar to that observed prior to treatment.     

Fatty acid composition of Cladocera and Copepoda from lakes of contrasting temperature

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Movements of brown trout, Salmo trutta, and juvenile Atlantic salmon, Salmo salar, in a coastal stream in northern Norway

Movements of resident brown trout (age 2+ to 9+ years) and young Atlantic salmon (age 1+), stocked as fry, were studied in July, August and September in a coastal stream in northern Norway. Between 85 and 89% of the brown trout were recaptured in the study area (346m, 1326m²) within 45m of their release point throughout the investigation period. Most specimens had moved less than 150m. Trout movements were related to local variation in density. Trout occupying those sections of stream with the lowest fish densities (5.3–10.9 fish 100m^?2) had a significantly lower movement rate than fish from sections with densities between 13.7 and 31.5 fish 100m^?2. Trout that moved from their marking section were significantly larger than specimens that did not leave their original site. There was a significant correlation between permanence of station each month and the mean water level that month. The majority of the trout (47%) were caught at undercut stream banks or at sites in the proximity of these. A decrease in water level during the study period resulted in a high loss (36%) of such habitat, probably forcing some individuals to move. The recapture data indicate that the trout population consists of one small (c. 15–20%) mobile, and one large sedentary component. Young salmon displayed high station permanence in July and August (93% and 96%). However, in the autumn they exhibited a significant downstream movement, and only 73% were recaptured within their release section. This movement was significantly higher for larger specimens, and is thought to occur because of a pre-winter change in habitat, initiated by a decline in stream temperature. In contrast to trout, salmon in sections containing the lowest densities (22.0–25.0 fish 100m^?2) did not show significantly lower movement rates when compared with salmon at higher densities (32.2–46.3 and 51.8–60.6 fish 100m^?2). The spatial distribution of young salmon indicated the formation of territorial mosaics over the stream bed, which are thought to reduce intraspecific competition.