Temporal variations and pond age effect on plankton communities in semi-intensive freshwater marron (Cherax cainii,Austin and Ryan, 2002) earthen aquaculture ponds in Western Australia

The abundance and diversity of the plankton community represents the health of the aquatic ecosystem, and plays an important role in the growth of cultured animals under aquaculture conditions. The temporal variations of plankton abundance, taxonomic composition, diversity, evenness and species richness were studied in three old and three new semi-intensive marron (Cherax cainii, Austin and Ryan, 2002) ponds. Water parameters such as temperature, dissolved oxygen, pH, turbidity, TAN, nitrite, nitrate and reactive phosphate were recorded, and plankton samples were collected every two months, for one year of juvenile production cycle. A total of twenty-six phytoplankton and seven zooplankton genera were recorded. Chlorophyceae was the dominant class of phytoplankton throughout the year, followed by Trebouxiophyceae. Rotifera comprised 49.8% of the total zooplankton community (individuals L^?1), the largest proportion of any group. Temporal variations impacted the plankton abundance and community structure, and plankton abundance were more abundant during summer. The pond age did not influence the phytoplankton abundance, whereas zooplankton abundance was higher in older ponds.     

Effects of food type on diel behaviours of common carp Cyprinus carpio in simulated aquaculture pond conditions

In order to better understand behaviour patterns of common carp Cyprinus carpio in aquaculture ponds, their diel grazing, swimming, resting and schooling behaviours were observed in six 1 m² tanks under simulated pond conditions. Each tank was fertilized to stimulate natural food production before starting experiments, and then stocked with three C. carpio . Fish behaviours were compared among three treatments: (1) tanks with plankton only, (2) tanks with plankton and benthic macroinvertebrates and (3) tanks with plankton, benthic macroinvertebrates and artificial feed. Overall C. carpio grazed more frequently during daytime than at night and exhibited the reverse pattern for non-feeding swimming behaviour. A significant negative relationship ( r ² = 0·99, P < 0·01, n = 48) was observed between total per cent grazing time and total per cent swimming time. Fish dispersed to graze individually during daytime but schooled at night and did not display any agonistic behaviours. Diel variations in the vertical swimming behaviour of C. carpio were related to food types available. In tanks containing plankton only, fish grazed in the water column, whereas when benthic macroinvertebrates were present, they spent more time near the tank bottom. Resting behaviour was only seen in tanks with artificial feed and even then was rare (2–5% of total time). Results suggest that C. carpio growth and feed utilization efficiency in semi-intensive aquaculture systems could be optimized by using a combination of plankton, benthic macroinvertebrates and artificial feed, and feeding fish twice per day (at c . 0730 and c . 1630 hours).     

Water level and fish-mediated cascading effects on the microbial community in eutrophic warm shallow lakes: a mesocosm experiment

Information on the effects of water level changes on microbial planktonic communities in lakes is limited but vital for understanding ecosystem dynamics in Mediterranean lakes subjected to major intra- and inter-annual variations in water level. We performed an in situ mesocosm experiment in an eutrophic Turkish lake at two different depths crossed with presence/absence of fish in order to explore the effects of water level variations and the role of top-down regulation at contrasting depths. Strong effects of fish were found on zooplankton, weakening through the food chain to ciliates, HNF and bacterioplankton, whereas the effect of water level variations was overall modest. Presence of fish resulted in lower biomass of zooplankton and higher biomasses of phytoplankton, ciliates and total plankton. The cascading effects of fish were strongest in the shallow mesocosms as evidenced by a lower zooplankton contribution to total plankton biomass and lower zooplankton:ciliate and HNF:bacteria biomass ratios. Our results suggest that a lowering of the water level in warm shallow lakes will enhance the contribution of bacteria, HNF and ciliates to the plankton biomass, likely due to increased density of submerged macrophytes (less phytoplankton); this effect will, however, be less pronounced in the presence of fish.     

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.     

Interdependence of plankton spatial distribution and plancton biomass temporal oscillations: mathematical simulation

The dynamics of aquatic biological communities in a patchy environment is of great interest in respect to interrelations between phenomena at various spatial and time scales. To study the complex plankton dynamics in relation to variations of such a biologically essential parameter as the fish predation rate, we use a simple reaction-diffusion model of trophic interactions between phytoplankton, zooplankton, and fish. We suggest that plankton is distributed between two habitats one of which is fish-free due to hydrological inhomogeneity, while the other is fish-populated. We show that temporal variations in the fish predation rate do not violate the strong correspondence between the character of spatial distribution of plankton and changes of plankton biomass in time: regular temporal oscillations of plankton biomass correspond to large-scale plankton patches, while chaotic oscillations correspond to small-scale plankton patterns. As in the case of the constant fish predation rate, the chaotic plankton dynamics is characterized by coexistence of the chaotic attractor and limit cycle.     

Microbial food web in a large shallow lake (Lake Balaton, Hungary)

Seasonal variations of phyto-, bacterio- and colourless flagellate plankton were followed across a year in the large shallow Lake Balaton (Hungary). Yearly average chlorophyll-a concentration was 11 µg 1^–1, while the corresponding values of bacterioplankton and heterotrophic nanoflagellate (HNF) plankton biomass (fresh weight) were 0.24 mg 1^–1 and 0.35 mg 1^–1, respectively. About half of planktonic primary production was channelled through bacterioplankton on the yearly basis. However, there was no significant correlation between phytoplankton biomass and bacterial abundance. Bacterial specific growth rates were in the range of 0.009 and 0.09 h^–1, and ended to follow the seasonal changes in water temperature. In some periods of the year, predator-prey relationships between the HNF and bacterial abundance were obvious. The estimated HNF grazing on bacteria varied between 3% and 227% of the daily bacterial production. On an annual basis, 87% of bacterial cell production was grazed by HNF plankton.     

“Green water” microalgae: the leading sector in world aquaculture

Freshwater fish culture is generally considered the largest sector in world aquaculture. Several of the leading species consume “green water” plankton. This plankton—mostly microalgae (phytoplankton) and also bacteria, protozoa and zooplankton—grows in man-made fertilized water impoundments. The quantity of “green water” microalgae consumed by fish and shrimp is estimated here at a quarter billion ton fresh weight a year, about three and a half times as much as the entire recognized aquaculture. This estimate is based on the quantities of the microalgae consumed and the efficiencies of their use for growth by the main species in aquaculture. The cost of producing “green water” microalgae by the aquaculturists—mostly in SE Asia—is low. The populations in “green water” are biologically managed by the cultured fish themselves. The fish with their different feeding habits help “manage” the composition of the plankton and the overall water quality as they grow. The aquaculturists further manage “green water” through simple means, including water exchange and fertilization. Cost is remunerated partially by the income from sales of the fish and partially by bio mitigation services that “green water” polyculture ponds provide the aquaculturists in treating farm and household waste. A comprehension of the scale and importance of the microalgae sector to world aquaculture should lead to more research to improve understanding of algal population dynamics, growth factors, and efficiency of food chains. The consequent improved control of the plankton’s interaction with fish and shrimp production in “green water” will undoubtedly contribute much to the expansion in production of seafood.     

Zooplankton biomass variation in relation to climatic conditions in the Barents Sea

Over the last two decades, there have been large changes in the zooplankton biomass in the Barents Sea. These biomass variations are mainly attributed to predation pressure and environmental factors (e.g. advective transport). When stock size of capelin (Mallotus villosus), a major planktivorous fish in the Barents Sea ecosystem, was quite low as in 1986 and 1994, the zooplankton biomass showed marked increase. However, the increase in the zooplankton biomass occurred in different water masses during 1986 and 1994. In 1986, a climatically cold year, the plankton biomass was highest in the Arctic waters of the northeastern Barents Sea. This is probably due to the increase in larger Arctic amphipod species, such as Themisto libellula. In 1994, a climatically warm year, the zooplankton biomass was high in the Atlantic waters of the southwestern Barents Sea. The large increase in zooplankton biomass in the Atlantic waters in 1994 was presumably due to the higher inflow of advected organisms, e.g. Calanus spp., as well as high temperatures, which may lead to high growth rates of zooplankton. Throughout the studied region, the plankton biomass in the "cold year" of 1986 was generally much lower than in the "warm year" of 1994.     

Chaos and Peak-to-Peak Dynamics in a Plankton–Fish Model

A plankton–fish model, comprising phosphorus, algae, zooplankton, and young fish, with light intensity and water temperature varying periodically with the seasons, is analyzed in this paper. For realistic values of the parameters the model behaves chaotically, but its dynamics within the strange attractor can be described by a few one-dimensional maps that allow one to forecast the next yearly peak of plankton or fish from the last peaks. This property is an unambiguous mark of a special form of chaos. Unfortunately, the estimate of such peak-to-peak maps from field data is possible only if plankton or young fish biomass has been sampled accurately and frequently for a paramount number of years. In conclusion, the analysis shows that it might be that plankton dynamics are characterized by an interesting and peculiar form of chaos, but that inferences from recorded data on the existence of these forms of chaos are premature.     

A simple method of feeding coregonid larvae on frozen zooplankton

7 days old larvae of Coregonus lavaretus L. (local name: ‘Blaufelchen’) were fed on zooplankton that had been frozen at—18°C for 1 year. 4 times per day the pieces of frozen plankton were added into the preaeration tank thus providing that freshly thawed zooplankters were offered to the fish. Within 10 weeks the fish reached a total length of 30.5 ± 5.5 ram and an average dry weight of 22 mg. Within this period the survival was 45 % of the initial number. After a period of 7 weeks feeding on long-term frozen pankton 400 fish were switched to living zooplankton and after 9 weeks 400 fish were switched to short-term frozen plankton. The growth of those fish that were fed on living plankton was significantly faster than it was when frozen zooplankton was given. A switch of coregonids which were prefed on frozen zooplankton to dry diet proved to be successful as soon as the fish had reached a body length of 40 mm.     

Comparative plankton ecology of five fish tanks in Delhi,India

Summary A comparative account of the plankton ecology of five fish tanks in Delhi is given.Variations in the physical and chemical characteristics of water such as temperature, turbidity, total residue, pH, free carbon dioxide, carbonate alkalinity, total alkalinity, total hardness, chlorides, dissolved oxygen, oxygen consumed, phosphates, nitrates, silicates and sulphates observed for a period of one year are described. Chemical characteristics of water vary to a great extent in the five tanks. The dry summer and the monsoon rains considerably influence the physical and chemical conditions of water.The quantitative variations in the phytoplankton populations are presented. Compared to temperate waters, the tanks in Delhi show a richer variety of organisms. The largest number of genera is noted among the green algae. Desmids are poorly represented in all the tanks. The phytoplankton populations show a regular winter maximum which is caused by diatoms.Observations on the quantitative variations in the major groups of zooplankton are presented. Zooplankton population is represented by many genera. The dominant group among the zooplankton is the Rotifera which shows a summer maximum.There is no significant correlation between the phytoplankton and the zooplankton.Part of the thesis approved for the Ph. D. Degree of the University of Delhi, 1961.     

Simulated annual plankton production in the northeastern Pacific Coastal Upwelling Domain

A microcomputer simulation model is presented that describesthe generalized plankton production dynamics, in the surfacemixed layer, of the Juan de Fuca Eddy located on the southwesternBritish Columbia continental shelf. The Juan de Fuca Eddy simulationmodel evaluates how the annual biomass production of diatoms,copepods and euphausiids is forced by plankton feeding interactions,seasonal variability in upwelling, water temperature and solarradiation, and generalized fish predation. The model estimatesannual primary production of 345 g C m^–2 year^–1and secondary production of 19.4 g C m^–2 year^–1for copepods and 6 g C m^–2 year^–1 for euphausiids,during 1985–89; -90% of the annual plankton productionwas generated during the April-October upwelling season. Perturbationsof 22 abiotic and biotic parameters, one at a time by ±10%of nominal values, indicated that oceanic variability (e.g.upwelling rate) most strongly affected primary production. Conversely,zooplankton production was most sensitive to variability inbiological parameters describing zooplankton grazing potentialand growth (e.g. gross growth efficiency). Simulated seasonalbiomass patterns of diatoms, copepods and euphausiids were foundto closely match empirical data. However, euphausiid biomassproduction in the Juan de Fuca Eddy alone was unable to meetthe demands of estimated pelagic fish consumption. Local Eddyeuphausiid populations had to be supplemented, from regionaleuphausiids. by a mechanism that is proposed to be linked tothe seasonal pattern and intensity of positive Ekman transport(upwelling).     

Observations on the incidence and seasonal fluctuations of certain crustacean larvae in the plankton of the South-West Coast of India

The seasonal fluctuations in the incidence of planktonic organisms and the larval forms of certain crustaceans such as crabs, barnacles and post larvae of prawns in the plankton of the south-west coast of India have been followed for a period of three years from 1963. South-west monsoon period is the least productive period for zooplankton in this area. Brachyuran zoeae, post larvae of prawns and barnacle nauplii occur in the plankton throughout the year with distinct peaks for different groups. The zoeae ofUca annulipes occur in the plankton from September to May with a peak during November–December. The zoeae ofPortunus pelagicus are present in the plankton from September to June and their abundance is in February–March. The post larvae ofMetapenaeus affinis are found in the inshore plankton from November to June with the peak in March. The nauplii ofBalanus amphitrite communis occur in the plankton in all the months of the year, the peak incidence has been during November January. The zoeae ofU. annulipes are found to tolerate better the medium saline conditions. Of the ecological factors, salinity of the ambient water and the availability of planktonic food for the larvae seem to influence the seasonal fluctuations of these crustacean larvae in this locality.     

Role of body size and temporal hydrology in the dietary shifts of shortjaw tapertail anchovy Coilia brachygnathus (Actinopterygii, Engraulidae) in a large floodplain lake

Seasonal water-level changes in floodplain lakes can induce variations in primary and secondary production, thus affecting trophic interactions. In this study, we tested the latter by studying size- and temporal hydrology-related shifts in the diet of shortjaw tapertail anchovy Coilia brachygnathus (Actinopterygii, Engraulidae) from Lake Poyang. During the wet season, δ¹³C values ranged from ?28.2‰ for small anchovies to ?24.6‰ for larger individuals, but δ¹⁵N ranged from 18.9‰ for smaller fish to 12.4‰ for larger fish. Significant ¹³C-enrichment and ¹⁵N-depletion occurred with increasing size, revealing that different carbon sources were used as the fish grew. Given the high hydrologic fluctuation levels, significant differences in δ¹³C values were observed among larger anchovies between seasons, indicating a temporal dietary shift. Anchovies fed primarily on shrimp and fish during the low-water season despite the predominance of zooplankton during the two seasons studied, which indicated increased piscivorous reliance. C. brachygnathus exhibited higher δ¹⁵N values during the wet season because the food items were ¹⁵N-enriched. Human waste brought by floods could be another possible interpretation. Considering C. brachygnathus is an important link between plankton production and higher piscivorous trophic levels, changes in the species are expected to affect the functioning of lake food webs along the trophic pathway.     

Growth and production of the dominant pelagic fish, Acanthobrama terraesanctae, in subtropical Lake Kinneret, Israel

Acanthobrama terraesanctae (local name lavnun), an endemic planktivorous cyprinid, dominates total fish numbers (>80%) in Lake Kinneret, and may have a significant top-down impact on the lake ecosystem. The length of young-of-the-year fish calculated from the von Bertalanffy equation agreed with field observations of juvenile growth. An unusual bi-modal length-frequency distribution observed in May 1993 provided additional help in age identification. Males grew more slowly than females and reached a lower maximum length. Total mortality coefficients (exponents) of males and females >12 cm (minimal legal size of fish in the catch) were similar ( c. 1·52). An average cohort reaches maximum biomass during its second year. Maximum production is created at the end of the second year. The production: biomass ratio of the population was 1·16, and 36% of total lavnun standing stock was taken by fishing. From the late 1980s to early 1990s, when standing stock and population structure were stable, the average harvest of 1000 t was consistent with a total lavnun biomass of 2800 t, which constitutes 50–70% of the total fish stock measured acoustically in the lake. Such a biomass could be sustained by the known production of zooplankton. Absence of verified growth data for lavnun contributed to the collapse of the fishery in 1993, because it hampered timely revision of fishery policy in response to the drastic changes in the lavnun stock in 1992.     

Annulus formation on scales and seasonal growth of the Central Amazonian anostomid Schizodon fasciatus

Annulus formation on the scales of the Central Amazonian anastomid fish Schizodon fasciatus was studied with respect to periodic variations in growth rates caused by seasonal inundation or associated biological processes. Monthly samples from fish markets were analysed with regard to marginal scale increment, feeding index, condition factor, gonadosomatic index, and body cavity fat content. There was a significant variation in all indices which was related to seasonal change in water level. Fat storage was related to energy requirements especially during gonad maturation. Fastest growth was observed during the period of falling water level. The formation of scale growth marks corresponded to the period of gonad maturation between January and February. The results indicate the formation of only one single growth mark on scales per year.     

Age,growth and reproductive biology ofNotothenia squamifrons gunther, 1880 from the Indian sector of the Southern Ocean

Summary The growth ofNotothenia squamifrons is analysed using scale reading of specimens from various isolated areas of the Indian sector of the Southern Ocean (Kerguelen, Crozet and Marion Islands; Ob, Lena and Kara-Dag seamounts). Studying reproductive biology reveals that spawning is annual and occurs during austral spring. Hatching takes place in summer. Scaling is set during the autumn. The smallest scaled fish measure 3.8 cm in total length. The data mentioned above, the check number on the scales and the sampling dates lead to the identification of the different age groups. Differences in growth rate appear between the studied areas. The fastest growth is observed around the Kerguelen Islands where the oldest specimens are 19 years old and reach 52 cm in total length. On the other hand, in the Crozet population,N. squamifrons does not live more than 12 years for a maximum length of 30 cm. Scale reading in fish from the Ob and Lena seamounts shows a minor decrease in growth during the winter season when compared to that in the other areas. The hydrographical conditions of this sector of the Southern Ocean may, in part, explain these differences: especially temperature and plankton biomass seem to effect growth rate. The cold antarctic waters and the highest plankton productivity, inducing the optimal growth rate, are found in the Kerguelen Islands.     

Comparative metabolomics of the diatom Skeletonema marinoi in different growth phases

We introduce a rigorously validated protocol based on extraction, derivatisation and GC/MS for the analysis of diatom metabolomes. Using this methodology we characterised general patterns of the metabolism of the diatom Skeletonema marinoi during different growth phases. Canonical analysis of principal coordinate revealed clearly that the intracellular metabolites differ between exponential, stationary and declining phase. In addition, diurnal variation during the exponential phase was observed. A detailed analysis of the metabolic changes is presented and discussed in the context of previous physiological studies of diatoms. The observed variability in metabolites has a significant consequence for further physiological and ecological studies. Investigations have to take into account that diatom metabolism is a highly dynamic process and that food quality, chemical defence and also the production of signal molecules might be dependent on different growth phases or diurnal variations. The introduced protocol is in general suitable for the monitoring of microalgae and has also the potential to be applied to complex plankton communities.     

Nitrogen and phosphorus in plankton

Summary The total nitrogen and phosphorus content in the plankton of Porto Novo water has been investigated. The total nitrogen content varied from 0.28% to 11.70% depending upon the organisms studied. In the same organism or same group of organisms the peak values were noted during the peak season of that plankton. The phosphorus content in the different planktonic organisms varied from 0.0620% to 0.8025% dry weight. Here also the peak values coincided with a peak population of the organism. During a rich diatom period, the phosphorus content in both water (as phosphate) and the diatoms showed a significant rise. However, with a peak zooplankton season, the phosphate in the water did not show any increase.

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Sommario La quantita di nitrogene e di fosforo contenuta nel Plankton delle acque di Poroto Nuovo è stata studiata.La quantità di nitrogeno varia dal 0.28% al 11.70% a seconda degli organismi studiati. Nello stesso organismo di uno stesso gruppo — i valori massimi furono notati durante la stagione alta di quel Plankton.Il fosforo contenuto nei differenti organismi del plankton varia dal 0.0620% el 0.8025% a secco. Anche qui i massimi valori coincidono colla massima concentrazione degli organismi.Durante un periodo ottimale di diatome, il fosforo contenuto sia nell, acque (come fosfato) e nei diatome, mostrava un significativo aumento. Viceversa con la punta massima del zooplankton, il fosfato nell'acqua non rivelava nessum aumento.