Growth and production of five species of Ephemeroptera larvae from an experimental recirculating stream

SUMMARY. The production and growth of the larvae of five species of Ephemeroptera in an experimental recirculating stream-channel are described. The most abundant species were Baetis rhodani , which achieved a maximum population density of c. 29,000 m^-2 in August, and Ephemerella ignita which reached a density of c. 13,000 m^-2 in the spring. Three other common speeies, Paraleptophlebia submarginata, Centroptilum luteolum and Caenis rivulorum were present at lower densities (< 1000 m^-2). B. rhodani had five cohorts in a year whilst C. luteolum had two or possibly three. E. ignita, C. rivulorum and P. submarginata were univoltine. Mean speeifie growth rates were calculated for each species, the maximum being 3.26±0.49% length day^-1 for E. ignita (3 April—15 May). Production of each of these five species of Ephemeroptera was calculated giving a total annual production of 10.2 g dry wt m^-2 (computational method).     

The life history and production of the leech Helobdella stagnalis (Hirudinea:Glossiphonidae) in the River Ely, South Wales

SUMMARY. A population of the glossiphonid leech Helobdella stagnalis was studied over a period of 16 months in the organically polluted River Ely, South Wales. There were two generations each year. The overwintering population released young (the spring-brood) in June. The spring-brood in turn produced their own offspring (summer-brood) in August.
Seasonal patterns of mortality were related to flow, temperature and life-cycle stage. Individual growth rates were dependent upon both temperature and life-cycle stage.
Annual population production (P) was 7.56 g wet wt m^-2, mean annual population biomass (B) was 1.43 g wet wt m^-2 and the annual P/B ratio was 5.29.     

A carbon budget for nematodes, rotifers and tardigrades in a Swedish coniferous forest soil

Nematodes, rotifers and tardigrades from a Swedish pine forest soil were investigated in a monthly sampling programme lasting for one year. The monthly mean values of number, biomass and oxygen consumption were estimated. All groups fluctuated rather much over the year with a summer minimum (1.1 ˙ 10⁶ animals m^-2) and a winter maximum (6.3 ˙ 10⁶ animals m^-2) for the nematodes. The reasons for these fluctuations are discussed in relation to fluctuations of water content and temperature of the soil. On an annual basis a carbon budget was calculated which gave the following values for this fauna; consumption 4.3, production 0.6, respiration 0.9 and defecation 2.8 g carbon m^-2.     

The life history and production of Asellus aquaticus (Crustacea: Isopoda) in the River Ely, South Wales

SUMMARY. A population of the isopod Asellus aquaticus was studied for sixteen months in the organically polluted River Ely. South Wales. There were two complete generations each year. The overwintering population released young (the spring-brood) over the period April-June. These animals in turn produced their own offspring (summer-brood) in late July-October. Each generation died after breeding and the overwintering population was comprised entirely of animals from the summer-brood.
Seasonal patterns of mortality were related to water flow, temperature and life-cycle stage. Individual growth rates were affected by both temperature and life-cycle stage.
Annual population production (P) was 195.68 g wet wt m^-2, mean annual biomass (B) was 32.98 g wet wt m^-2 and the annual P/B ratio was 5.93.     

A modified drop-net method for sampling mobile epifauna on marine shallow sandy bottoms

The seasonal variations in numbers and biomass of the mobile epifauna of a shallow, sandy bay in Gullmar Fjord (Sweden) was investigated during 1976–1977 using the drop-net technique. Juvenile plaice, Pleuronectes platessa L., sand goby, Pomatoschistus minutus (Pallas), and brown shrimp Crangon crangon L. are the dominant epifaunal species. A net enclosing an area of 100 m² was used, and the organisms captured were collected with a small trawl. Three stations with a water depth≤ 1 m were regularly sampled with a total number of 73 drops. Maximum abundance was for plaice in June (6 ind m^-2), for the shrimp in July-August (61 ind m^-2), and for sand goby in September (2 ind m^-2). Standing stocks (dry wt) were 0.2, 1.5 and 0.2 g m^-2 respectively. Production estimates were based on seasonal changes in size frequency and information on specific growth rates. The production rate was for plaice (0-group) 0.3 g m^-2 yr^-1, for the shrimp 1.5, and for sand goby 0.2 g m^-2 yr^-1. Reliable estimates of the absolute abundance can be derived from the mean catch per unit area only when the efficiency of the fishing gear is known. After 6 hauls with the trawl in the drop-net enclosure more than 85% of the shrimps were caught and after the fifteenth haul less than 1% were still left. The fishing efficiency of a push-net in relation to the drop-net was for the shrimp 50%, for plaice 35% and for sand goby 17%.     

The life cycle, population dynamics, growth and secondary production of the snail Xeropicta arenosa Ziegler (Gastropoda: Pulmonata) in northern Greece

The life cycle, population dynamics and secondary production of the xerothermophilic land snail Xeropicta arenosa were studied in northern Greece. The study of biology and the demographic analysis of the populations of X. arenosa revealed that it is a semelparous annual species. Reproduction takes place in autumn and the majority of the adults die after egglaying. Growth is continuous throughout the year and no seasonal fluctuations occur. Estimation of annual secondary production with the Hynes' size frequency method revealed a mean standing crop ( aa ) of 0.075 g m^-2 year^-1 and a productivity ( P ) of 0.267+ 0.043 gm^-2 year^-1. The annual turnover ratio ( P/ ) was equal to 3.56.     

Energetics of a population of Asellus aquaticus (Crustacea, Isopoda): respiration and energy budgets

SUMMARY. Respiration of Asellus aquaticus was determined on tiine occasions throughout the year using a Gilson differential respirometer. On each occasion the determination was made at the lake temperature, which ranged from 2 to 18°C, Linear regressions were derived for log oxygen uptake against log dry weight. There was a significant difference between mean rates of oxygen uptake at the various temperatures but the slopes of the regression lines, which varied from 0,62 to O.85 with a mean of 0,76, were not significantly different.
The temperature of the lake was monitored throughout the year. Using the relationship of oxygen uptake against temperature, and estimates of population density obtained previously, the total annual respiration of the population was calculated as 4571 ml O₂ m^-2, equivalent to an energy loss of 92.3 kj m^-2 year^-1 from a mean biomassof 752 mg m^-2.
Consumption of decayed Alnus glutinosa leaves and faecal production rates, and thus assimilation efficiency, were determined by gravimetric methods in the laboratory at 10°C, close to the mean temperature of the lake (10.rC), In the four size classes investigated, larger animals consumed more food per individual, but less on a weight specific basis. However, it was shown that consumption was greater if the leaf material was more highly decomposed, Assimiliation efficiency was calculated as 23%.
Using data for respiration, population density and the assimilation efficiency, the annual population energy budget was estimated as (kJ m^-2year^-1): consumption, 568.9 (100%); production, 38.5 (6.8%); respiration, 92.3 (16.2%); faeces, 438.1 (77%). The significance of these energy values, and the ecological efficiencies calculated from them, are discussed in relation to other published work.     

Energy partitioning in the Antarctic collembolan Cryptopygus antarcticus

Abstract. 1. Consumption, production and assimilation rates were determined for two age groups of Crypropygus antarcticus to give an estimate of energy utilization, and to investigate low temperature adaptation in its energy partitioning.
2. Feeding selectivity shown in laboratory preference tests was supported by gut analysis of field animals from contrasting sites. Although moulting rate was not significantly affected by food type, rates of growth were slowest and mortality highest when fed on a non-preferred substrate.
3. Both a radio labelling and a more direct method for measuring dry weight consumed gave similar results for Cvpropygus feeding on algae. The consuniption rate for animals when feeding on algae was lower than that on moss peat. The assimilation efficiency for immature animals feeding on algae was 46% and for mature animals was 19%; the values when feeding on moss peat were 7% and lo%, respectively, The net production efficiency ranged from 35%(inimatures) to 13% (matures) and was similar on both substrates.
4. Food consumption exceeded assimilation over the range 2.5–10°C, but the two converged from 2.5 to 0°C. Immature Cryptopygus maintained a net positive energy balance over 0–10°C, whilst below 1S°C respiration exceeded assimilation for mature individuals.
5. An estimate of the annual dry matter consumption (7 g m^-1 y^-1) by Ctypropygus in a moss turf at Signy Island agrees with one based on respiration data alone (Davis, 1981). The consumption at an alga-dominated site was c . 26 g m^-2 y^-l, and Crypropygus may have a locally limiting effect on net priniary production at such sites.     

The growth rate of eel in tributaries of the lower River Severn, England, and its relationship with stock size

The growth rate of 1980 eel Anguilla anguilla from 15 sites in the Severn system varied between 16·4 and 27·9 mm year^-1, density from 0·12 to 1·14 m^-2 and biomass from 2·56 to 25·24 g m^-2. There was no significant relationship between growth rate and density or biomass ( P > 0·05).     

Peat respiration and decomposition in Antarctic terrestrial moss communities

Oxygen uptake by the peat of two Antarctic bryophyte communities (a moss turf and a moss carpet) is converted to organic matter loss and used to derive the rate of decomposition. The decay rates obtained in this way are evaluated in two mathematical models which simulate the accumulation of dead organic matter (DOM) in the communities from the litter production and decomposition rate. Litter production, the extent of DOM accumulations at present on the sites and mean decomposition rates (i.e. fraction of standing crop lost per year) were 409 g m^-2 year^-1, 33.5 kg m^-2 and 0.017 g g^-1 year^-1 in the moss turf and 392 g m^-2 year^-1, 29.6 kg m-² and 0.010 g g^-1 year^-1 in the moss carpet respectively (all weights expressed as dry weight). Aerobic decomposition rate declined with depth in both communities. From the model's predictions it is suggested that the observed decay rate was too high in the moss turf and too low in the carpet. Possible reasons for this are discussed and suggestions made for future work.     

Life cycle, production, microdistribution and diet of the damselfly Euphaea decorata (Odonata: Euphaeidae) in a Hong Kong forest stream

Euphaea decorata in Tai Po Kau Forest Stream (Hong Kong) was univoltine. Most recruitment took place in summer, and larval growth proceeded throughout the year. Life-cycles recorded in 1977–78 and 1978–79 were similar. Annual production estimates, using the removal-summation, instantaneous growth and size-frequency methods, were more similar for the 1978–79 generation (ranging from 158.7–174.7; mean 1671 mg dry wt m^-2) than for the 1977–78 generation (93.9-173-6; mean 131.7 mg dry wt m^-2). Mean biomass was similar for both generations (ranging from 33.5–33.9 mg dry wt m^-2), and mean P/B ratios were 3.9 1977–78) and 5.0 (1978–79). These are the first estimates of annual production by an Oriental stream insect.
Larvae were most abundant at microsites in the middle of the stream. Multiple regression analysis indicated that substratum characteristics were a major determinant of microdistribution. Euphaea decorata apparently favoured poorly-sorted sediments with highly peaked grain size-frequency distributions, containing few fine particles.
The carnivorous larvae showed ontogenetic changes in diet. Small individuals consumed mainly chironomid (Diptera) larvae; the diet expanded to include (successively) larvae of Ephemeroptera and Trichoptera as E. decorata grew. Seasonal changes in diet were also apparent, although larval diets during spring and summer were similar. There was also considerable overlap between autumn and winter diets. Ontogenetic influences upon prey consumed were not sufficient to account for the observed seasonal differences.     

Observations on the growth and production of chub Leuciscus cephalus and dace Leuciscus leuciscus in a small lowland river in southeast England

SUMMARY. The River Eden (Kent, England) holds a mixed coarse fish population in which minnows ( Phoxinus phoxinus ), gudgeon ( Gobio gobio ), chub ( Leuciscus cephalus ) and dace ( Leuciscus leuciscus ) are numerically predominant. Chub and dace provide the major interest to anglers and their growth and production were studied. Observed growth rates of both species were marginally below recorded averages from other British habitats. Back-calculations showed that year-class strength and relative growth rates varied between years. Instantaneous mortality rate Z was 0.147 for chub aged 1–10, 0.438 for chub aged 10 and over, and 0.172 for dace. Exclusive of the 0-group, fish numbers, biomass (wet wt) and production were found to be 0.1305 m^-2, 19.12 gm^-2 and 5.38 gm^-2 year^-1, respectively, for chub and 0.0968 m^-2, 4.33 gm^-2 and 1.69 gm^-2 year^-1 for dace. Smoothing of data produced theoretical production figures of 6.69 gm^-2 year^-1 for chub and 1.15 gm^-2 year^-1 for dace.     

Biomass and production estimates of a fish community in a small South African estuary

The fish community of the small (17·5 ha) intermittently open East Kleinemonde estuary was sampled between 1994 and 1997 to estimate population size, standing stock, growth and productivity. The estuarine-spawning species were numerically more abundant ( n c . 750 000) but due to their small size contributed only 11·7% to the total biomass. The total annual productivity of all fishes in the estuary ( n c . 890 000), with a standing stock of 28·44 g m ⁻², was calculated at 55·89 g m⁻² year⁻¹. The small sparid Rhabdosargus holubi with a production estimate of 41·35 g m⁻² year⁻¹ accounted for <74% of the total fish production in this estuary.     

Life cycle, growth, mortality and production of Ephemerella major Klapalek (Ephemeroptera) in a trout stream in Belgium

SUMMARY. 1. The life cycle of Ephemerella major Klapalek in a chalk trout stream in Belgium took 1 year. Emergence was highly synchronized with a flight period from mid-May to mid-June. Tiny nymphs occurred from June to late August.
2. The mean instantaneous growth rate was high in autumn (3.6% wet wt day⁻¹), very low from November to February (0.8% wet wt day⁻¹) and high until emergence (2.3% wet wt day⁻¹); short day length seemed to be the major factor reducing growth rate during winter.
3. Mortality was close to zero during winter and 1.4—1.7% day⁻¹during other seasons. Total mortality from egg to adult was 99.6%.
4. The annual production was about 9g wet wt m⁻² year⁻¹ and the annual P/ ratio was 7.5. There was good agreement between the production values estimated by four methods. Production rate was highest in May (13 mg wet wt m⁻² day⁻¹) and zero in February.     

Litter decomposition by slugs in mixed deciduous woodland

For the one year period considered, it is calculated that 683.5 g m^-2 plant litter entered the study area site. Of the six slugs studied, Arion intermedius Normand, the smallest species, had the highest overall consumption rate on the nine test foods (29.1 ± 0.9 mg dry wt g live wt^-1 d^-1) and the highest overall mean assimilation efficiency (72.0 + 0.9%). The mean faecal production for each of the six slug species was very similar, ranging from 8.4 to 9.9 mg dry wt g live wt^-1 d^-1. Using regression equations of food consumed on faeces produced, it is estimated that the slug fauna each year consumes 8.4% of the leaf litter input and 6.5% of the total available plant litter. Of the plant material consumed, 13.8 g dry wt m^-2 are deposited annually as faeces. The role of slugs in decomposition processes is discussed and compared with that of other soil organisms.     

The life cycle and growth of Sialis lutaria L. (Megaloptera) in a drainage channel under different methods of plant management

Abstract. 1. The life cycle of Sialis lutaria in two experimental reaches, one treated with the herbicides dalapon and 2,4-D (Chemical) and the other subjected to a conventional method of plant control (Hand), of a drainage channel in Essex took about 2 years.
2. A maximum density of 815 m^-2 was recorded and the density of each year class in both reaches generally decreased exponentially with age.
3. At certain times of the year the mean individual weight of each year class increased exponentially with age. Annual production was estimated to be 985 (Hand) and 1171 (Chemical) mg dry weight m^-2, with ratios of annual production to mean standing crop (P: ) of 1.6 and 1.8 respectively.
4. There was no evidence that the use of herbicides had any discernible effect on the mortality, growth or production of S.lutaria.     

Production of epipelic algae before and during lake fertilization in a subarctic lake

Epipelic production was studied over three years in Lake Gunillajaure, a small, subarctic lake in northern Sweden. In 1977 the lake was in its natural state and in 1978 and 1979 it was continuously fertilized with phosphorus and nitrogen. The fertilizations in 1978 and 1979 did not increase the annual epipelic production measured with ¹⁴C technique. Also the seasonal production pattern was the same during the three years. The variation in production with depth was similar all three years with mean values of 85 mg C m^-2 d^-1 at 2 m and 1 mg C m^-2 d^-1 at 11 m. Light penetration and water temperature were found to be the most important environmental factors affecting epipelic production. A long turnover time, between I months and 14 yr at different depths, of the probably well adapted epipelic community is suggested to be an explanation to the absence of a response to the fertilization.     

The production of brown trout, Salmo trutta in tributaries of the Upper Wye, Wales

The population density, age structure, biomass, growth and production of brown trout were investigated in four tributaries of the upper River Wye. The populations at each site were largely maintained by immigration from nursery areas. Abundance of separate year classes at sites on the three largest tributaries reached a peak at age 2+. On the smallest stream numbers reached a peak at 1+. Recruitment occurred throughout the year but decreased with age of year classes. Maximum O+ densities ranged from 0.04 to 0.89 m⁻², and >0+ densities from 0.13 to 0.59 m⁻². Average total biomass in 1975 ranged from 2.6 to 14.2 g m⁻². Within the study sites annual trout production in 1975 ranged from 2.9–19.7 g m⁻². Production values were dependent on age structure and population mobility at the study sites. In the three largest streams 2+ and 3+ fish contributed 66.3–88.3% of total production whilst 1+ and 2+ fish contributed 74.5–84.5 % of the total in the smallest stream. The mobile (non-resident) component of the population accounted for up to 60–70% of production at certain times of the year, but over the year (1976) accounted for =30 % of total production. The resident component of the highest annual production value (19.7 g m⁻²) was estimated to be between 15.0 and 18.2 g m⁻².     

Production and litter processing by crayfish in an Appalachian mountain stream

SUMMARY 1. Mean annual density and biomass () of Cambarus bartonii in an Appalachian mountain stream (U.S.A.) was 12 individuals m⁻² and 1669 mg (ash-free dry weight) m⁻².
2. Annual production ( P ) of C bartonii was 961 mg AFDW m⁻². Despite high biomass, low growth rates resulted in low production and a low P/ ratio of 0.58.
3. While C bartonii constituted 61% of the total macroinvertebrate biomass, it contributed only 13% of annual community secondary production.
4. Litter processing was positively related to temperature and crayfish size. Cambariis bartotnii was estimated to comminute 36 g m⁻² y⁻¹ of leaf litter (>1 mm²) to 24 g m−^>2 y⁻¹ fine particulate material (<1 mm²). The annual pattern of litter comminution by crayfish was regulated by temperature. As a result, >5()% of shredding activity by crayfish occurred from June to September which was also the period of lowest litter standing crops and activity of other shredding macroinvertebrates.
5. We speculate that during summer crayfish play an important role in temperate woodland streams by converting slowly processed leaf litter species (e.g. Rhododendron ) to fine particles which are then available to collector-gatherers (e.g. Chironomidae, Oligochaeta).     

LIGHT-DEPENDENT GROWTH, DARK SURVIVAL, AND GLUCOSE UPTAKE BY CRYPTOPHYTES ISOLATED FROM A FRESHWATER CHEMOCLINE

Clones of Cryptomonas phaseolus Skuja , Cryptomonas rostratiformis ( Skuja ) Skuja in Huber-Pestalozi, and Cryptomonas undulata Gervais were isolated from the deep chlorophyll maximum near the oxic/anoxic boundary layer of the mesoeutrophic lake Schlachtensee, Germany. Different autecological features of these species were studied in batch culture experiments . Cryptomonas cf . ovata Ehrenberg and Chroomonas sp. that never dominated in the deep chlorophyll layer were also isolated from Schlachtensee to study their light-dependent growth in comparison to the deep-living species . Cryptomonas undulata, C. cf . ovata, and C. phaseolus had a very low light compensation point ( 5–7 μmol.m^-2.s^-1 ), whereas the growth rate of Chroomonas sp. and C. rostratiformis was positive above 16 and 24 μmol.m^-2.s^-1 . Cryptomonas phaseclus and Chroomonas sp. became photoinhibited above photon flux densities of 92 and 116 μmol.m^-2.s^-1 . Cryptomonas rostratiformis, C. cf . ovata, and C. undulata reached a maximum growth rate at a considerably higher photon flux density (198–250 μmol.m^-2.s^-1 ). Cryptomonas phaseolus grew fastest under light-limiting conditions . Chyptomonas phaseolus and C. undulata were best able to suruive prolonged periods of darkness . Cryptomonas phaseolus, C. rostratiformis, and C. undulata did not show any uptake of fluorescent latex beads. When labeled glucose was provided in naturally occurring concentrations, carbon uptake by C. phaseolus, C. rostratiformis, and C. undulata was negligibly small in comparison to cellular carbon content. I suggest that the adaptation to a low-light environment is an important preadaptation for the dominance of C. phaseolus and C. undulata near the freshwater chemocline .