The life cycle dynamics and production of zooplankton in Øvre Heimdalsvatn

The zooplankton in Øvre Heimdalsvatn was studied from May 1969 to Aug 1973 in order to obtain knowledge about their functioning and role in the lake ecosystem. The paper concentrates on the main species: Holopedium gibberum, Bosmina longispina, Cyclops scutifer. Heterocope saliens, Conochilus unicornis, Polyarthra vulgaris and Kellicottia longispina but Megacyclops gigus, Daphnia longispina and ciliated cells are also considered. The development of the populations was fairly synchronized and made it possible to determine life cycles, development times, growth, reproduction and production from field data. The total production of the multicellular zooplankton was 2–3 mg dry wt m⁻² yr⁻¹. The cladocerans dominated and their share of the total was 84–92% compared to the copepods 5–8% and the rotifers 3–8%. The ciliate production was not estimated, but their biomass exceeded that of the copepods and rotifers. The spring spate, June temperatures, food availability and invertebrate predation were found to be the most important regulatory factors for life cycle dynamics and production. Allochthonous organic matter was found to be a necessary food resource in addition to algae.     

Phytoplankton ecology in an Antarctic lake

SUMMARY. The ecology of the phytoplankton of Heywood Lake, Signy Island, South Orkney Islands, Antarctica was investigated during 1969–72. The lake, which is ice-covered for 8–10 months per year, is moderately eutrophic due to enrichment by seal excreta.
The annual cycle of the phytoplankton is described. During the winter (approximately May-September), very few algal cells could be detected in the water column and ¹⁴C fixation was below measurable limits. In spring (October-November), a rapidly-growing population of algae caused a large increase in the chlorophyll- a concentration (maximum value 170 mg m⁻²) but carbon fixation remained low, with values <500 mg C m⁻² day⁻¹. The algae contributing to this peak were mainly small chlorophytes and chrysophytes. The summer open-water period (December-March) was characterized by a different phytoplankton population dominated by cryptophytes. Chlorophyll levels were lower ( c . 40 mg m⁻²) but ¹⁴C fixation rates >3 g C m⁻² day⁻¹ were measured on bright days. Values for Assimilation Number were very high (maximum value 10.5 mg C h⁻¹ mg⁻¹ (chlorophyll- a ) in January (1971) though temperatures never exceeded 8°C. In autumn, the phytoplankton regressed to winter levels. Both spring and summer algal populations probably overwinter as resting stages.     

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.     

The lake ecosystem of Øvre Heimdalsvatn

The Norwegian subalpine lake. Øvre Heimdalsvatn, has a surface area of 0.78 km² and a maximum depth of 13 m. It is ice-covered for 7.5–8 months, has a marked spring spate and a mean annual renewal period of about two months. The water is poor in electrolytes. Intensive studies have been made by an interdisciplinary team of the lake's physical and chemical properties, primary production and secondary production under the auspices of IBP/PF from 1969 to 1973, Allochthonous material accounted for 1/3 of utilized plant input. The major lake predator, the brown trout, fed largely on benthic organisms and did not exploit the zooplankton biomass. On account of the long period of ice cover and the rapid rise in temperature after ice break, many organisms (both planktonic and benthic) showed synchronous development. Abiotic conditions, such as the nature of the spring spate and the temperature rise, strongly affect species and community development.     

A limnological investigation of the tarn Syslaktjønn, W Norway

An investigation covering hydrography, chemistry, vascular and cryptogamic plants, nitrogen fixation, phytoplankton biomass and production, and zooplankton was carried out from April to November 1976 in tarn in W Norway, The volume of the tarn was 18000 m³ and the turnover time about 30 d. Temperature ranged between 3.6 and 23.4°C and pH between 4.8 and 5.5. Nuphar luteum and Carex rostrata were the two dominating vasculars-with biomasses of 117 and 97 g m⁻², respectively The biomass of the bryophytes ( Sphagnum spp.) was about 510 g m⁻² and the production of the order 0.2–2.1 μg (mg d.w.)⁻¹h⁻¹. Nitrogen fixation in association with Sphagnum spp. was estimated at 25 g yr⁻¹ for the whole tarn. Phytoplankton was dominated by diatoms, green algae and chrysophyceans. The chlorophyll a content ranged from 2 to 20 mg m⁻³ and the carbon assimilation rates from 0.03 to 20 mg C m⁻³h⁻¹ at 0–4 m depths. Production in the period was of the magnitude 22 g C m⁻². The copepod Eudiaptomus gracilis was the most common netzooplankter. Large numbers of rotationrians were found during summer.     

Comparative primary productivity of algal epiphytes on three species of macrophyte in the littoral zone of Lake Ohrid, Yugoslavia

Primary productivity of algal epiphytes on the surfaces of Phragmites, Potamogeton , and Nuphar was measured seasonally from June 1978, through June 1979, in the littoral zone of Lake Ohrid, using ¹⁴C methodology. Surface areas of individual macrophytes were determined throughout the study period through the use of a non-miscible surfactant and a calibration curve of surfactant weight versus known, calculated surface areas.
Mean total surface area available for epiphytic colonization during the study period was 1.032 m² macrophyte surface per m² of littoral zone for Phragmites , 0.810 m² for Potamogeton , and 0.167 m² for Nuphar . Seasonal rates of mean primary productivity of algal epiphytes on Phragmites from the surface to the light-compensation depth ranged from 84–1406 mg C m⁻² littoral zone d⁻¹; ranges for epiphytes on Potamogeton and Nuphar were 77–586 and 69–268 mg C m⁻² littoral zone d⁻¹, respectively. Maximum rates were observed typically during June; minimum rates were observed typically during August to December. Mean daily productivity rates over the 12 month period were for epiphytes on Potamogeton 167.0, on Nuphar 100.4 and on Phragmites 671.2 mg C m⁻² littoral zone d⁻¹. Calculated annual production for epiphytes on Nuphar was 36.65, on Potamogeton 60.95 and on Phragmites 245.0 g C m⁻² littoral zone yr⁻¹. Epiphytic production data were typically considerably higher than production data obtained for littoral and pelagial planktonic algae and compare favorably with published data for epiphytic and periphytic production in Lawrence Lake, Marion Lake, and Borax Lake.     

Holocene carbon burial by lakes in SW Greenland

The role of the Arctic in future global change processes is predicted to be important because of the large carbon (C) stocks contained in frozen soils and peatlands. Lakes are an important component of arctic landscapes although their role in storing C is not well prescribed. The area around Kangerlussuaq, SW Greenland (66–68°N, 49–54°W) has extremely high lake density, with ∼20 000 lakes that cover about 14% of the land area. C accumulation rates and standing stock (kg C m⁻²), representing late- to mid-Holocene C burial, were calculated from AMS ¹⁴C-dated sediment cores from 11 lakes. Lake ages range from ∼10 000 cal yr  bp to ∼5400 cal yr  bp , and reflect the withdrawal of the ice sheet from west to east. Total standing stock of C accumulated in the studied lakes for the last ∼8000 years ranged from 28 to 71 kg C m⁻², (mean: ∼42 kg C m⁻²). These standing stock determinations yield organic C accumulation rates of 3.5–11.5 g C m⁻² yr⁻¹ (mean: ∼6 g C m⁻² yr⁻¹) for the last 4500 years. Mean C accumulation rates are not different for the periods 8–4.5 and 4.5–0 ka, despite cooling trends associated with the neoglacial period after 4.5 ka. We used the mean C standing stock to estimate the total C pool in small lakes (<100 ha) of the Kangerlussuaq region to be ∼4.9 × 10¹³ g C. This C stock is about half of that estimated for the soil pool in this region (but in 5% of the land area) and indicates the importance of incorporating lakes into models of regional C balance at high latitudes.     

A relationship between irradiation, carbohydrates and rooting in cuttings of Pisum sativum

Rooting ability was studied for cuttings derived from pea plants ( Pisum sativum , L. cv. Alaska) grown in controlled environment rooms. When the cuttings were rooted at 70 μmol m⁻² s⁻, ¹ (photosynthetic photon flux density) or more, a stock plant irradiance at 100 μmol m⁻² s⁻¹ decreased rooting ability in cuttings compared to 5 μmol m⁻², s⁻¹, However, cuttings rooted at 160 μmol m⁻² s⁻¹ formed more roots compared to 5 (μmol m⁻² s⁻¹. Although a high irradiance increased the number of roots formed, it could not overcome a decreased potential for root formation in stock plants grown at high irradiance. Light compensation point and dark respiration of cuttings decreased by 70% during the rooting period, and the final levels were strongly influenced by the irradiance to the cuttings. Respiratory O₂ uptake decreased in the apex and the base of the cutting from day 2 onwards, whereas a constant level was found in the leaves. Only the content of extractable fructose, glucose, sucrose and starch varied during the early part of the rooting period. We conclude that the observed changes in the cuttings are initiated by excision of the root system, and are not involved in the initiation of adventitious roots.     

The Ephemeroptera of Øvre Heimdalsvatn

The species composition, distribution, seasonal variations in abundance, life cycles, emergence periods, length-weight relationships and biomass of the Ephemeroptera of Øvre Heimdalsvatn were investigated. Detritus was a significant factor in explaining the variation in total ephemeropteran numbers around the lake. Numbers in the exposed zone reached a maximum during July due to emergence activity. The ephemeropteran biomass at emergence, to which Leptophlebia vespertina (L.), L. marginata (L.) and Siphlonurus lacustris Eaton were the main contributors, was estimated to be 0 02g dw m⁻². Other species recorded from the lake were Baëtis macani Kimmins, B. rhodani Pictet, Siphlonurus aestivalis Eaton and Ameletus inopinatus Eaton. All species were univoltine, but differences in ability to grow during ice cover and in life cycle timing resulted in a succession in emergence during the ice free period.     

Sublittoral abundance and food consumption of Baltic gobies

Two small demersal fishes, the sand goby Pomatoschistus minutus and the common goby Pomatoschistus microps , were quantified on soft bottoms at 20–40 m depth in the Baltic Sea, using a camera placed above the bottom. The largest numbers of gobies were seen following the settlement of young in late summer and autumn. Most recorded fishes were sand gobies. An annual average of 4·7 individuals m⁻²(0·24 g dry mass m⁻²) was recorded in 1983–1985 and 2·5 individuals m⁻²(0·13 g m⁻²) in 1997–1998. Using these densities, the annual goby food consumption was estimated to 100 kJ m⁻² in 1983–1985 and 50 kJ m⁻² in 1997–1998, corresponding to most of the annual macrobenthos production available to the gobies. The resulting goby production, assumed equal to 25% of the food consumed, must have been an important food source for the larger fishes occasionally recorded in the photographs.     

A light intensity threshold for schooling in the Atlantic mackerel, Scomber scombrus

The schooling behaviour of Atlantic mackerel was studied in a large tank at different light intensities in the range 12.6–1.8 × 10⁻¹⁰μEs⁻¹ m⁻². Variable light intensity was produced by accurately controlling the current to a green light-emitting diode (LED) 3 m above the experimental tank. Under high light levels (1.8 × 10⁻⁶μEs⁻¹ m⁻²) mackerel always formed a single school, whereas at lower levels (1.8 × 10⁻⁸μEs⁻¹ m⁻²) they swam as individuals. At light levels down to 1.0 × 10⁻⁶μEs⁻¹ m⁻² the mean nearest neighbour distance in a school remained relatively constant (0.3–0.9 body lengths), and individual mackerel swam along a path which deviated from the position of their nearest neighbours by less than 14°. As light dropped below 1.8 × 10⁻⁷μEs⁻¹ m⁻², both nearest neighbour distance and heading angle between nearest neighbours increased, with mean values of 1–1.8 body lengths and 23–92°, respectively, at 1.8 × 10⁻⁹μEs⁻¹ m⁻². The results are discussed in terms of ambient light conditions in the sea.     

Introduction of the European minnow into a subalpine lake: habitat use and long-term changes in population dynamics

Minnows Phoxinus phoxinus , studied 30 years after the first record of the species in the subalpine Lake Øvre Heimdalsvatn, Norway, ≥55 mm L _T, were estimated to have densities of c . 4.7 kg ha⁻¹ (120 000 fish) in June 1999 and 2.1 kg ha⁻¹ (63 000 fish) in June 2000. The population was characterized by low individual growth, delayed age of maturity and lived longer when compared to values reported in a previous study in the early phase of its establishment, and other values reported in the literature. Most minnows reached sexual maturity at 4–5 years and >55 mm L _T. Although the estimated annual survival of minnows >55 mm was low ( S =0.2), ages up to 13 years were recorded. Despite a moderate increase in the population size during the last 20 years, the present reduction in individual growth, followed by delayed age of maturity, suggested the existence of density-dependent effects on the population dynamics of the minnows. The minnows were restricted to the littoral zone and near bottom areas. A vertical or horizontal expansion in habitat use was probably prevented by the presence of piscivorous brown trout Salmo trutta .     

Photophobic stop-response in a dinoflagellate: Modulation by preirradiation

Gyrodinium dorsum Kofoid responds photophobically to flashes of blue light. The photophobic response consists of a cessation of movement (stop-response). Without background light and after a flash fluence above 10 J m⁻², 75–85% of the cells show a stop-response, while only 50% of the cells show this response at 5 J m⁻². With a flash fluence of 5 J m⁻², background light of different wavelengths either increases (614 nm. 5.5–18.2 μmol m⁻² s⁻¹) or decreases (700 nm, 18.4–36.0 μmol m⁻² s⁻¹) the stop-response. Two hypotheses for the mechanism of the modulation by background light of the photophobic response are discussed: an effect of light on the balance of the photosynthetic system (PS I/PS II) or an effect on a phytochrome-like pigment (P_r/P_fr). This study supports the idea that a phytochrome-like pigment works in combination with a blue light-absorbing pigment. It was also found that cells of Gyrodinium dorsum cultured in red light (39.8 μmol m⁻²) had a higher absorption in the red region of the absorption spectra than those cultured in white light (92.7 μmol m⁻²).     

DEVELOPMENT OF PROTOPLASTS OF ULVA FASCIATA (CHLOROPHYTA) FOR ALGAL SEED STOCK

The aim of this study was to isolate and cultivate protoplasts of the green alga Ulva fasciata Delile and subsequently induce them to form a microthallus suspension for algal seed stock. The protoplasts were covered with secreted mucilage following 6 h of culture when viewed with SEM. The mucilage fused to form thick layers during day 1 of culture. Microfibrillar cell walls were deposited into the thick layers of mucilage on the 5th day of culture. An average of about 10% of the freshly isolated protoplasts began to divide at 6–14 days. These protoplasts subsequently developed varied morphologies, depending on the time of collection during the year. Protoplasts isolated from U. fasciata collected in March to June developed frond thalli or microthalli when they were cultured in low or high densities (cells/area), respectively. The microthallus suspension was cultured for more than two years at 10–40 μ mol·m^{− 2} ·s^{− 1} . Frond thalli formed when the suspension was cultivated at 100–160 μ mol·m^{− 2} ·s^{− 1} . Therefore, microthallus suspension can serve as a seed stock of U. fasciata .     

Ecological changes in a lake fishery and their effects on a stunted roach Rutilus rutilus population

Data for two sampling years (1969/70 and 1970/71) is presented to illustrate the changing composition, density and biomass of the macroinvertebrate fauna in a South Lancashire lake. Six faunal groupings are recognised for a non-parametric analysis of the data and significance levels are given for the between-station and between-year differences recorded. The mean density of macroinvertebrates (1.2 mm mesh sieve) estimated for the lake as a whole increased by 28.5% in the second year (2519 m⁻²-3237 m⁻²) whereas the estimated mean biomass in g m⁻² increased by 86% wet weight (8.61−16.01) and 196% dry weight (1.74−5.15). Molluscs contributed substantially to the increased standing crop which was accompanied by increased development of macrophytes.
A comparative study of the diets of roach in two size groups in winter and summer is described. The variety of food items consumed was found to be greater than in a preliminary study in May 1969 and, for the roach sampled, the average quantity of food consumed per fish increased after the 1969/70 winter. The possible relationships between invertebrate standing crop, roach diet and previously reported changes in the growth of the roach are discussed and an explanation is offered concerning the sequence of biological changes observed in the lake.     

Influence of solar ultraviolet radiation on photosynthesis and motility of marine phytoplankton

Abstract: The effects of solar ultraviolet radiation (UV) on carbon uptake, oxygen evolution and motility of marine phytoplankton were investigated in coastal waters at Kristineberg Marine Research Station on the west coast of Sweden (58° 30'N, 11° 30'E). The mean irradiances at noon above the water surface during the investigation period were: photosynthetic active radiation (PAR, 400–700 nm) 1670 μmol m⁻² s⁻¹; ultraviolet-A radiation (UV-A, 320–400 nm) 35.9 W m⁻² and ultraviolet-B radiation (UV-B, 280–320 nm) 1.7 W m⁻². UV-B radiation was much more attenuated with depth in the water column than were PAR and UV-A radiation. UV-B radiation could not be detected at depths greater than 100–150 cm. Inhibition of carbon uptake by UV-A and UV-B in natural phytoplankton populations was greatest at 50 cm depth and the effects of UV-B were greater than those of UV-A. At depths greater than 50 cm there was almost no effect of ultraviolet radiation on carbon uptake. PAR, UV-A and UV-B decreased oxygen evolution by the dinoflagellate Prorocentrum minimum . Inhibition of oxygen evolution was greater after 4 h than 2 h but it was not possible to distinguish the negative effects of the different light regimes. The motility of P. minimum was not affected by PAR, UV-A and UV-B. The importance of exposure of phytoplankton to different light regimes before being exposed to natural solar radiation is discussed.     

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.     

Modelling black fly production dynamics in blackwater streams

SUMMARY. 1. Two predictive models were employed along with intensive field sampling to estimate production of black flies ( Simulium spp.) on snags (submerged wood) in three blackwater streams on the Georgia Coastal Plain of the southeastern U.S.A. One model predicts daily growth rate from temperature and hydrograph pattern; the other predicts habitat abundance (of snags) from river height.
2. In the sixth order Ogeechee River, annual production was twice as high in 1982 (7.1 g dry mass [=DM] m⁻² of snag surface) as in 1983 (3.6 g DM m⁻²). When converted to production per m² of river bottom, values were 35–40% of the snag surface estimates. Annual production was much lower in fourth order Black Creek (1982, 1.3 g DM m⁻² of snag surface) and much higher in the sixth order Satilla River (1975, 15.6–40.0 g DM m⁻²).
3. There was a distinct bimodal pattern of black fly production in the Ogeechee River in both years, with peaks occurring in winter and summer. Similar bimodal patterns of production were found in Black Creek and in the Satilla River. Although there appears to be an intrinsic component to the bimodal pattern, production peaks (growth rate and biomass) appear to be associated with initial stages of flooding.
4. Annual production/biomass ratios (37–85) are the highest reported for black fly populations. The variation of annual P/B ratios among sites was more strongly dependent on the temporal distribution of standing stock biomass than on differences in growth rates. Variation in production among sites appears to be due to differences in current velocity, hydro-graph variability, and abundance of coexisting consumers.     

Population dynamics and feeding of mayfly larvae in some acid and alkaline New Zealand streams

SUMMARY. 1. Population dynamics (density, biomass, annual production), gut contents and feeding rates of mayflies ( Deleatidium spp.; Leptophlebiidae) were compared in two naturally acid (mean pH≃4.8). brownwater streams and two alkaline (mean pH 7.5), clearwater streams in South Westland, New Zealand.
2. Mean densities of larvae (range 234–2318 m⁻²) were higher in alkaline streams on most of the six bimonthly sampling dates. Mean biomass (range 0.020–0.376 g larval dry weight (LDW) m⁻²) was always highest at the stable, spring-fed, alkaline site and was lower at the acid sites and another alkaline site where the population was always dominated by small larvae.
3. Annual production was high at the more stable, alkaline site (10.35 gLDW m⁻²) but much lower at the other sites (2.49–3.77 g m⁻²).
4. Gut contents of larvae were dominated by fine (45–75 μm widest diameter) paniculate matter (69–99%), diatoms (up to 21%) and. at one site, filamentous algae (8–13%).
5. Grazing rates of mayflies on epilithon were significantly higher on stones taken from acid than alkaline streams and material grazed from the former contained a higher proportion of inorganic material (87–93% and 61–83% inorganics, respectively).
6. Higher grazing rates may reflect lower quality of epilithic food in acid, brownwater streams, a factor that could contribute to the lower productivity of Deleatidium populations at these sites.     

Potassium dependence and phytoplankton ecology: an experimental study

SUMMARY 1. Unialgal cultures of three species common in the freshwater phytoplankton were used to test limitation of specific growth rate and final yield in defined media of low K⁺ concentration (range <0.3–6 μmol L⁻¹ or mmol m⁻³).
2. Growth rate of the diatom Asterionella formosa was independent of K⁺ concentration above 0.7 μmol L⁻¹. Final yield was dependent on initial concentration when accompanied by K⁺ depletion below this concentration, but not by lesser depletion with more residual K⁺. Analyses of particulate K in the biomass indicated a mean final cell content of 2.8 μmol K 10⁻⁸ cells, approximately 1.0% of the organic dry weight.
3. Less detailed work with the diatom Diatoma elongatum showed no dependence of growth rate or final yield upon the initial K⁺ concentration in the range 0.8–3.2 μmol L⁻¹. The phytoflagellate Plagioselmis nannoplanctica suffered net mortality in the lowest concentration tested, 0.8 μmol L⁻¹.
4. Comparison with the range of K⁺ concentration in natural fresh waters, including a depletion induced by an aquatic macrophyte, suggests that K⁺ is unlikely to limit growth of phytoplankton. Nevertheless, there can be correlation of K⁺ with lake trophy.