Zooplankton Growth Research Articles

Demographic responses of selected rotifers (Rotifera) and cladocerans (Cladocera) fed toxic Microcystis aeruginosa (Cyanobacteria)

Tropical waterbodies contain several species of toxic cyanobacteria including Microcystis, which adversely affect the somatic growth, survival and fecundity of zooplankton. Scenedesmus, one of the most common green algae, is even found in Microcystis -dominated waterbodies. It is, therefore possible that in natural ponds, rotifers and cladocerans feed on mixed phytoplankton species containing algae and cyanobacteria. In this work, we quantified demographic responses of three rotifer species (Brachionus calyciflorus, B. rubens, and Plationus patulus), and three cladoceran species (Simocephalus mixtus, Daphnia cf. mendotae and Moina macrocopa) fed toxic Microcystis aeruginosa only or mixed with Scenedesmus acutus. The highest population growth for both rotifer and cladoceran species was observed when Scenedesmus was offered alone or at 75 % of the diet. Daphnia cf. mendotae and B. rubens were less affected by Microcystis while M. macrocopa and B. calyciflorus were more adversely influenced, which was also corroborated by life table demography. In competition bioassays, D. cf. mendotae was more efficient, alone or in competition, when fed with 50 or 25 % of Microcystis. This work explains the dynamics of the zooplanktonic community against gradual changes in phytoplankton due to the presence of cyanobacteria.

Zooplankton growth and survival differentially respond to interactive warming and acidification effects

AbstractThe copepod Acartia tonsa is a key component of a wide range of marine ecosystems, linking energy transfer from phytoplankton to higher trophic levels, and has a central role in productivity and biogeochemistry. The interaction of end-of-century global warming and ocean acidification scenarios with testing moderate temperature effects on a seminatural copepod community is needed to understand future community functioning. Here, we deployed a mesocosm experimental set-up with a full factorial design using two temperatures (13°C and 19°C) crossed with a pCO2 gradient ranging from ambient (550 μatm) to 3000 μatm. We used the natural bacteria, phyto- and microzooplankton species composition and biomass of the Kiel Bight and tested the response of A. tonsa development, carbon growth, mortality, size and condition. The tested traits were differently affected by the interaction of temperature and acidification. Ocean acidification increased development, carbon growth, size and mortality under the warming scenario of 19°C. At 13°C mortality rates decreased, while carbon growth, size and condition increased with acidification. We conclude from our experimental approach that a single species shows a variety of responses depending on the focal functional trait. Trait-specific mesozooplankton responses need to be further investigated and compared between geographical regions, seasons and taxonomic groups.

The potential of zooplankton in constraining chytrid epidemics in phytoplankton hosts.

Fungal diseases threaten natural and man‐made ecosystems. Chytridiomycota (chytrids) infect a wide host range, including phytoplankton species that form the basis of aquatic food webs and produce roughly half of Earth's oxygen. However, blooms of large or toxic phytoplankton form trophic bottlenecks, as they are inedible to zooplankton. Chytrids infecting inedible phytoplankton provide a trophic link to zooplankton by producing edible zoospores of high nutritional quality. By grazing chytrid zoospores, zooplankton may induce a trophic cascade, as a decreased zoospore density will reduce new infections. Conversely, fewer infections will not produce enough zoospores to sustain long‐term zooplankton growth and reproduction. This intricate balance between zoospore density necessary for zooplankton energetic demands (growth/survival), and the loss in new infections (and thus new zoospores) because of grazing was tested empirically. To this end, we exposed a cyanobacterial host (Planktothrix rubescens) infected by a chytrid (Rizophydium megarrhizum) to a grazer density gradient (the rotifer Keratella cf. cochlearis). Rotifers survived and reproduced on a zoospore diet, but the Keratella population growth was limited by the amount of zoospores provided by chytrid infections, resulting in a situation where zooplankton survived but were restricted in their ability to control disease in the cyanobacterial host. We subsequently developed and parameterized a dynamical food‐chain model using an allometric relationship for clearance rate to assess theoretically the potential of different‐sized zooplankton groups to restrict disease in phytoplankton hosts. Our model suggests that smaller‐sized zooplankton may have a high potential to reduce chytrid infections on inedible phytoplankton. Together, our results point out the complexity of three‐way interactions between hosts, parasites, and grazers and highlight that trophic cascades are not always sustainable and may depend on the grazer's energetic demand.

Nutrient and organic matter dynamics in Lake Glubokoe

In this paper we present the results of field observations carried out at Lake Glubokoe (Moscow Region) in 2017–2019. Basic characteristics of the vertical distribution of main nutrient elements (phosphorus, nitrogen, and silicon) and organic matter (COD and chlorophyll-a) content are shown, along with their seasonal ranges. Due to the lack of surface runoff into the lake, the concentrations of total phosphorus and nitrogen are generally low throughout the year, with almost total depletion of inorganic phosphorus in the epilimnion during the growing season. Sufficient microbial activity allows most of the inorganic nitrogen to be presented in the nitrate form, except for late summer and fall, when plankton death rate exceeds bacterial nitrification capacity. During the period of hypolimnetic anoxia, significant amounts of mineral phosphorus and ammonia nitrogen are released from the bottom sediments. COD value shows a correlation with the intensity of both phyto- and zooplankton growth, which also affect the nutrient content.

Ecosystem contribution by microbial loop in Bohai Bay, China,a numerical study

The contributions of the microbial loop to the ecosystem in the Bohai Bay, China was studied in this paper. An eco-hydrodynamic model coupled with pelagic and benthic systems was developed, and the comparison between the numerical results and the field survey data shows that the model is able to reproduce the growth curves for ecological variables in the Bohai Bay. The contributions of the microbial loop and new production of nitrogen (new nitrogen) on other ecological variables were investigated using the coupled model. The results demonstrate that the average contributions of the microbial loop to zooplankton growth were 0.0644, 0.134, 0.0873, 0.0590 mmol C m−3 for spring, summer, autumn and winter in pelagic ecosystem of the Bohai Bay, respectively, with the annual mean value being 372.28 mg⋅m−3⋅a−1 in the Bohai Bay. The contribution rate of new production of nitrogen through the sediment–water interface ranges from 17.2% to 56.0%, with the average value being 41.1%.

Effects of sumithion on growth and production of phytoplankton and zooplankton in aquaculture ponds

Sumithion is an organophosphorous pesticide widely used to control tiger bug in the fish larval rearing pond. The present study was aimed to investigate the effects of sumithion on plankton population abundance in aquaculture pond. The experiment was carried out with three treatments, i.e., ponds with no sumithion (T1), with 1.0 ppm sumithion (T2) and 2.0 ppm sumithion (T3). The water quality parameters, such as temperature, pH, dissolved oxygen and total alkalinity were almost unchanged throughout the study period whereas transparency, NO3-N and PO4-P values were declined with increasing sumithion concentrations but differences were not significant (P > 0.05). No distinct changes were observed in phytoplankton population densities (x cells/L). On the other hand, the zooplankton population densities (x Ind./L) were significantly (P > 0.05) decreased with toxicity of sumithion after 30 days to end of experimental period in both T2 and T3 compared to control group (T1). The ranges of pH, organic carbon (%), available phosphorus (ppm) and total nitrogen (%) of pond bottom-sediment did not differ irrespective of the treatments. This study demonstrated that sumithion has adverse effects on zooplankton which may influence the production in aquaculture pond.

Petrologic and geochemical evidence for the formation of organic-rich siliceous rocks of the Late Permian Dalong Formation, Lower Yangtze region, southern China

Abstract Black shales are economically and scientifically important because they are commonly associated with high-quality hydrocarbon source rocks and metal accumulations formed during periods of abrupt environmental change. Organic-rich siliceous rocks of the Late Permian Dalong Formation developed extensively within Middle–Upper Yangtze region (western Yangtze platform); however, the formation mechanism of its formation in the Lower Yangtze region (eastern Yangtze platform) remains a subject of debate due to a lack of outcrop exposure. Petrologic, mineralogic, and geochemical data are presented for three sections of the Dalong Formation within the Lower Yangtze region. Geochemical ratios including V/(V + Ni), V/Cr, Ni/Co, U/Th, and V/Sc suggest that the Dalong Formation was deposited in an oxygen-poor environment. The elevated concentration of Mo (>100 ppm) further suggests that free H2S existed in the bottom water, which was favorable for the accumulation of large amounts of organic matter. Mo/TOC ratios reveal that water flow in the Lower Yangtze Basin was moderately to strongly restricted during deposition of the Dalong Formation. Flow within the upper–middle parts of the Yangtze Basin was also restricted, suggesting that northern marginal basins on the Yangtze Platform formed part of a single ocean during the Late Permian (i.e., Changhsingian). Cherts of the Dalong Formation reflect high primary productivity, similar to that of modern-day upwelling zones, which increased the amount of organic matter. These results, combined with previous work, suggest that the long-term oxygen-poor conditions during deposition of the Dalong Formation were caused by restricted water circulation in a unique paleogeographic environment characterized by low latitude and submarine paleo-highlands. Such settings of low latitude characterized by tropical climate favored the growth of siliceous zooplankton in the zones with submarine paleo-highlands having created topographic barriers to water circulation. Restricted bottom-water flow and oceanic anoxia during the Late Permian were likely the main controls on the accumulation of organic-rich rocks. Elevated nutrient levels caused by frequent oceanic upwelling along the western margin of the South China Craton and global volcanism at this time facilitated siliceous organism productivity.

Combined effects of elevated carbon dioxide and temperature on phytoplankton-zooplankton link: A multi-influence of climate change on freshwater planktonic communities

It is essential to understand the combined effects of elevated CO2 and temperature on phytoplankton-zooplankton link when attempting to predict climate change responses of freshwater ecosystems. Phytoplankton species differ in stoichiometric and fatty acids composition, and this may result in phytoplankton-mediated effect on zooplankton at elevated CO2 and temperature. Beyond the isolated analysis of CO2 or temperature effect, few studies have assessed zooplankton growth under the phytoplankton-mediated effects of elevated CO2 and temperature. In this study, three algal species (green alga, diatom, cyanobacteria) were fed on zooplankton Daphnia magna, under the conditions of CO2 concentrations of ambient (390 ppm) and elevated (1000 ppm) levels and temperatures at 20, 25 and 30 °C. Elevated CO2 increased the algal biomass, while it reduced the phosphorus (P) and ω3 polyunsaturated fatty acids (ω3 PUFAs) to carbon (C) ratios. Elevated temperature decreased the P/C ratios in all algal cultures and ω3 PUFAs/C ratios in the diatom and the cyanobacteria cultures. Phytoplankton-mediated effect of elevated CO2 reduced the growth of zooplankton fed on the green and the mixed three algae culture. The stimulation of zooplankton fed on the diatom and the cyanobacteria by elevated temperature can be offset by decreasing food P and ω3 PUFAs contents. The combined effects of elevated CO2 and temperature on the growth of daphnids were mainly mediated by ω3 PUFAs/C ratios in the phytoplankton. Rising temperature as a combined direct and indirectly phytoplankton-mediated effect on zooplankton may be able to ameliorate the negative effects of elevated CO2. The results indicated that the combined effects of increased CO2 and temperature increased the fatty acid content of the green alga but not the other algae. This study highlighted that climate change with simultaneously increasing temperature and CO2 may entangle the carbon transfer in freshwater planktonic communities.

Consistent trophic amplification of marine biomass declines under climate change.

The impact of climate change on the marine food web is highly uncertain. Nonetheless, there is growing consensus that global marine primary production will decline in response to future climate change, largely due to increased stratification reducing the supply of nutrients to the upper ocean. Evidence to date suggests a potential amplification of this response throughout the trophic food web, with more dramatic responses at higher trophic levels. Here we show that trophic amplification of marine biomass declines is a consistent feature of the Coupled Model Intercomparison Project Phase 5 (CMIP5) Earth System Models, across different scenarios of future climate change. Under the business-as-usual Representative Concentration Pathway 8.5 (RCP8.5) global mean phytoplankton biomass is projected to decline by 6.1%±2.5% over the twenty-first century, while zooplankton biomass declines by 13.6%±3.0%. All models project greater relative declines in zooplankton than phytoplankton, with annual zooplankton biomass anomalies 2.24±1.03 times those of phytoplankton. The low latitude oceans drive the projected trophic amplification of biomass declines, with models exhibiting variable trophic interactions in the mid-to-high latitudes and similar relative changes in phytoplankton and zooplankton biomass. Under the assumption that zooplankton biomass is prey limited, an analytical explanation of the trophic amplification that occurs in the low latitudes can be derived from generic plankton differential equations. Using an ocean biogeochemical model, we show that the inclusion of variable C:N:P phytoplankton stoichiometry can substantially increase the trophic amplification of biomass declines in low latitude regions. This additional trophic amplification is driven by enhanced nutrient limitation decreasing phytoplankton N and P content relative to C, hence reducing zooplankton growth efficiency. Given that most current Earth System Models assume that phytoplankton C:N:P stoichiometry is constant, such models are likely to underestimate the extent of negative trophic amplification under projected climate change.

Modeling and analysis of inhibitory effect in plankton–fish model: Application to the hypertrophic Swarzedzkie Lake in Western Poland

The hypertrophic Swarzedzkie Lake, Poland, is characterized by high species diversity, abundance and biomass of both phytoplankton and zooplankton. A relationship has been observed only with size groups and/or living forms of a few taxonomical groups of phytoplankton and a negative effect is found in zooplankton growth rate due to these groups of phytoplankton. This paper is devoted to mathematical study of such influences of toxic grouped phytoplankton on zooplankton and fish populations. The tri-trophic reaction–diffusion model incorporates Holling type III and Monod–Haldane functional response for three state variables namely, phytoplankton, zooplankton and fish. In order to investigate the dynamics of model, we have analyzed local and global stability of both non-spatial and spatial model systems. We have proved Hopf-bifurcation for non-spatial model and discussed maximum sustainable yield as well as optimal harvesting policy for maximizing economic gain. Different conditions for Turing instability have been obtained for spatial model. Numerical simulation is carried out for both temporal and spatial models. The temporal model is numerically analyzed with the help of phase portraits, time evaluation and bifurcation diagrams. Very beautiful Turing patterns are observed for the diffusion induced model. Influences of inhibitory effect are numerically investigated in both zooplankton and fish populations. This mathematical study suggests that inhibitory effect is able to destabilize homogeneous steady state and also able to produce chaos in plankton–fish system.

Heterotrophic microbes upgrade food value of a terrestrial carbon resource for Daphnia magna

AbstractTerrestrial carbon resources are generally regarded as inferior‐quality food for zooplankton due to a lack of essential biomolecules (e.g., polyunsaturated fatty acids). However, recent stable isotopic studies have suggested terrestrial carbon to be substantial resource for zooplankton, though the mechanisms of assimilation are not well understood. Here, we consider the possibility that heterotrophic microbes can upgrade the nutritional value of terrestrial carbon and thereby support the somatic growth and reproduction of zooplankton. To test this hypothesis, a simplified experimental food chain was established. Aquatic microbes were raised under dark laboratory conditions on a terrestrial carbon source, decaying corn straw (Zea mays L.), and the resulting degradation products were supplied as food to Daphnia magna. Significant increases in microbial abundance and concomitant increases in polyunsaturated fatty acid were observed during the degradation of corn straw. Furthermore, experiments indicated that the somatic growth and reproduction of D. magna was supported exclusively by the products of corn straw decay. Our results indicate a pathway for the assimilation of terrestrial carbon by zooplankton, in which heterotrophic microbes serve as trophic links.

Fish-mediated plankton responses to increased temperature in subtropical aquatic mesocosm ecosystems: Implications for lake management

Although it is well established that climate warming can reinforce eutrophication in shallow lakes by altering top-down and bottom-up processes in the food web and biogeochemical cycling, recent studies in temperate zones have also shown that adverse effects of rising temperature are diminished in fishless systems. Whereas the removal of zooplanktivorous fish may be useful in attempts to mitigate eutrophication in temperate shallow lakes, it is uncertain whether similar mitigation might be achieved in warmer climates. We compared the responses of zooplankton and phytoplankton communities to climate warming in the presence and absence of fish (Aristichthys nobilis) in a 4-month mesocosm experiment at subtropical temperatures. We hypothesized that 1) fish and phytoplankton would benefit from warming, while zooplankton would suffer in fish-present mesocosms and 2) warming would favor zooplankton growth but reduce phytoplankton biomass in fish-absent mesocosms. Our results showed significant interacting effects of warming and fish presence on both phytoplankton and zooplankton. In mesocosms with fish, biomasses of fish and phytoplankton increased in heated treatments, while biomasses of Daphnia and total zooplankton declined. Warming reduced the proportion of large Daphnia in total zooplankton biomass, and reduced the zooplankton to phytoplankton biomass ratio, but increased the ratio of chlorophyll a to total phosphorus, indicating a relaxation of zooplankton grazing pressure on phytoplankton. Meanwhile, warming resulted in a 3-fold increase in TP concentrations in the mesocosms with fish present. The results suggest that climate warming has the potential to boost eutrophication in shallow lakes via both top-down (loss of herbivores) and bottom-up (elevated nutrient) effects. However, in the mesocosms without fish, there was no decline in large Daphnia or in total zooplankton biomass, supporting the conclusion that fish predation is the major driver of low large Daphnia abundance in warm lakes. In the fishless mesocosms, phytoplankton biomass and nutrient levels were not affected by temperature. Our study suggests that removing fish to mitigate warming effects on eutrophication may be potentially beneficial in subtropical lakes, though the rapid recruitment of fish in such lakes may present a challenge to success in the long-term.

Growth impacts of Saharan dust, mineral nutrients, and CO2 on a planktonic herbivore in southern Mediterranean lakes

Rising levels of CO2 can boost plant biomass but reduce its quality as a food source for herbivores. However, significant uncertainties remain as to the degree to which the effect is modulated by other environmental factors and the underlying processes causing these responses in nature. To address these questions, we carried out CO2-manipulation experiments using natural seston from three lakes under nutrient-enriched conditions (mimicking eutrophication and atmospheric dust-input processes) as a food source for the planktonic Daphnia pulicaria. Contrary to expectations, there were no single effects of rising CO2 on herbivorous growth. Instead, synergistic CO2 × nutrient interactions indicated that CO2 did not support higher zooplankton growth rates unless supplemented with dust or inorganic nutrients (nitrogen, N; phosphorus, P) in two of three studied lakes. The overall positive correlation between zooplankton growth and seston carbon (C), but not seston C:P, suggested that this was a food quantity-mediated response. In addition, we found that this correlation improved when the data were grouped according to the nutrient treatments, and that the response was largest for dust. The synergistic CO2 × nutrient effects reported here imply that the effects of rising CO2 levels on herbivorous growth may be strongly influenced by eutrophication processes and the increase in dust deposition predicted for the Mediterranean region.

The molecular basis of essential fatty acid limitation in Daphnia magna: A transcriptomic approach.

It is widely accepted that in many food webs, the trophic transfer efficiency among primary producers and herbivores is determined by the nutritional value of primary producers. In pelagic freshwater and marine ecosystems, secondary production by herbivorous crustacean zooplankton is often limited by the seston's content of essential ω3 polyunsaturated fatty acids (ω3 PUFAs). However, little is known about the genetic network behind the positive relationship between phytoplankton ω3 PUFA content and zooplankton growth and reproduction. In our experimental study, we analysed gene expression changes of the freshwater cladoceran Daphnia magna under different food regimes differing in their ω3 PUFA composition. To disentangle ω3 PUFA effects from other factors, we fed D.magna with different pure phytoplankton cultures (i.e., algal and cyanobacterial diets) with or without supplementing the essential ω3 PUFA eicosapentaenoic acid (EPA). As hypothesized, we observed enhanced growth on diets supplemented with EPA. We applied an Illumina RNA-seq approach to D.magna from different diet treatments to find and monitor genes that are regulated dependent on EPA availability. Of 26,646 potential protein products (mapped to the D.magna genome), we identified transcriptomic signatures driven by the different food sources. Further analyses revealed specific candidate genes involved in EPA metabolism, irrespective of the basal food source. This allows a first functional annotation of previously uncharacterized genes involved in the EPA-specific response of D.magna and may finally provide a link to molecular processes connected to ω3 PUFA metabolism and conversion and thus trophic transfer efficiency in pelagic food webs.

Zooplankton Abundance with NPK Fertilization

Zooplankton has advantages as natural feed for fish larvae. Therefore, necessary to attempts natural growth of zooplankton in aquaculture media, e.g. fertilization. This research aim to describe NPK Ferlitilizer influence to zooplankton abundance. Research conducted at January 2016, in Aquatic Resources Management Laboratory- Muhammadiyah University of Sukabumi and Water Quality Analysis in Center for Freshwater Aquaculture Laboratory. Research design is experimental research with four treatments and three replications. Treatment A with enhanced NPK fertilizer 10 ppm, Treatment B with NPK fertilizer 20 ppm, Treatment C with NPK fertilizer 30 ppm, Treatment D was control without fertilizer. Fertilizer treatment lead to water colour became green until dark green, officially different with control treatment. Zooplankton composition founded 78% from Eurotatoria, 19% from Branchiopoda, the left was from Malacostraca and Hexanauplia. Zooplankton abundance of control treatment significantly different with fertilizer treatment. The highest abundance found at the tenth day from treatment C with 18640 cell/L or almost 480% from initial.

A Model for Methylmercury Uptake and Trophic Transfer by Marine Plankton.

Methylmercury (MeHg) concentrations can increase by 100 000 times between seawater and marine phytoplankton, but levels vary across sites. To better understand how ecosystem properties affect variability in planktonic MeHg concentrations, we develop a model for MeHg uptake and trophic transfer at the base of marine food webs. The model successfully reproduces measured concentrations in phytoplankton and zooplankton across diverse sites from the Northwest Atlantic Ocean. Highest MeHg concentrations in phytoplankton are simulated under low dissolved organic carbon (DOC) concentrations and ultraoligotrophic conditions typical of open ocean regions. This occurs because large organic complexes bound to MeHg inhibit cellular uptake and cell surface area to volume ratios are greatest under low productivity conditions. Modeled bioaccumulation factors for phytoplankton (102.4-105.9) are more variable than those for zooplankton (104.6-106.2) across ranges in DOC (40-500 μM) and productivities (ultraoligotrophic to hypereutrophic) typically found in marine ecosystems. Zooplankton growth dilutes their MeHg body burden, but they also consume greater quantities of MeHg enriched prey at larger sizes. These competing processes lead to lower variability in MeHg concentrations in zooplankton compared to phytoplankton. Even under hypereutrophic conditions, modeled growth dilution in marine zooplankton is insufficient to lower their MeHg concentrations, contrasting findings from freshwater ecosystems.

The impact of calcium decline on population growth rates of crustacean zooplankton in Canadian Shield lakes

AbstractWithin the last decade, calcium decline has emerged as a stressor for many soft water lakes. A legacy of long‐term acid deposition and logging, calcium decline has been implicated in the loss of large herbivores, such as Daphnia, and changes in community structure as taxa with presumed low calcium demand also increase. Although lake surveys, paleolimnological studies, and laboratory experiments have provided considerable evidence that declining Daphnia abundances are associated with low calcium concentration, causal relationships for zooplankton response to calcium decline have not been assessed using field experiments with natural zooplankton communities. We conducted a six‐week field experiment under low food conditions typical of Canadian Shield lakes, using four calcium concentrations (0.6 mg/L, 1.0 mg/L, 1.4 mg/L, and 2.4 mg/L) and zooplankton communities originating from eight lakes along a gradient from 1.78 mg Ca/L to 24.8 mg Ca/L, to examine the effect of calcium on growth rates and reproduction of individual and groups of taxa. Population growth rates for daphniids, Bosmina spp., and three cyclopoids declined as calcium concentration decreased. At low calcium, growth rates of Daphnia pulex, Daphnia catawba, and Mesocyclops edax were negative indicating declining populations. There was no effect of calcium on reproduction of the most common cladocerans. Although we detected some variation in growth rates amongst source lakes, zooplankton communities did not differ in their response to low calcium. As calcium concentrations continue to decline in soft water lakes, reduced zooplankton growth rates may result in shifts in zooplankton community structure and overall declines in total zooplankton production.

Nitrogen effects on the pelagic food web are modified by dissolved organic carbon

Global environmental change has altered the nitrogen (N) cycle and enhanced terrestrial dissolved organic carbon (DOC) loadings to northern boreal lakes. However, it is still unclear how enhanced N availability affects pelagic food web efficiency (FWE) and crustacean zooplankton growth in N limited boreal lakes. Here, we performed in situ mesocosm experiments in six unproductive boreal Swedish lakes, paired across a DOC gradient, with one lake in each pair fertilized with N (2011: reference year; 2012, 2013: impact years). We assessed how zooplankton growth and FWE were affected by changes in pelagic energy mobilization (PEM), food chain length (phytoplankton versus bacterial production based food chain, i.e. PP:BP), and food quality (seston stoichiometry) in response to N fertilization. Although PP, PEM and PP:BP increased in low and medium DOC lakes after N fertilization, consumer growth and FWE were reduced, especially at low DOC—potentially due to reduced phytoplankton food quality [increased C: phosphorus (P); N:P]. At high DOC, N fertilization caused modest increases in PP and PEM, with marginal changes in PP:BP and phytoplankton food quality, which, combined, led to a slight increase in zooplankton growth and FWE. Consequently, at low DOC (<12 mg L−1), increased N availability lowers FWE due to mismatches in food quality demand and supply, whereas at high DOC this mismatch does not occur, and zooplankton production and FWE may increase. We conclude that the lake DOC level is critical for predicting the effects of enhanced inorganic N availability on pelagic productivity in boreal lakes.

Distribution and abundance of mesozooplankton in the Ross Sea, Antarctica

Zooplankton (meso- and macrozooplankton) distributions and biomass are poorly known in the Ross Sea despite their importance in energy transfer within food webs and biogeochemical cycles. Mesozooplankton abundance and biomass on the continental shelf are spatially variable and span two orders of magnitude during austral summer. Selected sub-regions (near the shelf break or ice shelf) show similar variability, suggesting that other processes, either oceanographic or biological, influence zooplankton on smaller scales. Biomass at one location (76.5° S, 172° E) was consistently elevated throughout January, although the causes of this “hotspot” were unclear. At a station near the ice shelf, abundance and biomass of the pteropod Limacina antarctica was very high. Zooplankton biomass at this location was sevenfold greater than any other station, and while the high biomass was driven by pteropod contributions, copepods were also abundant. Copepods dominated the mesozooplankton composition at all other stations, comprising 90 and 78% on average of the total abundance and biomass. Zooplankton biomass comprised on average 3.96% of the total particulate carbon (0–200 m) and was weakly correlated with chlorophyll and biogenic silica. We suggest that summer zooplankton growth and biomass, while linked to organic matter concentrations, are regulated by other factors (e.g., predation by crystal krill and Antarctic silverfish), as both grazers may be responsible for significant losses. Our data indicate that, contrary to other suggestions, summer zooplankton biomass and abundance in the Ross Sea are similar to those in other Antarctic coastal regions.

An analysis of how to improve production of copepods as live feed from tropical Taiwanese outdoor aquaculture ponds

The motivation for this study was to analyse the productivity of Taiwanese aquaculture ponds while providing recommendations for a more effective copepod harvesting. Hence, variations in copepod species composition, biomass and productivity were investigated during four separate 3weeks of intensive sampling campaigns across an annual season. The ponds showed seasonal changes, with relatively colder water at 20°C and lower chlorophyll-a in the winter (January 2014) compared to warm water 32°C and higher chlorophyll-a during the long summer season (April, July, October 2013). Differences between seasons were found for phytoplankton pigments concentration in the seston. Inorganic nutrients were never limited, and the average availability of phytoplankton such as diatoms and haptophytes was sufficient to support maximal growth of zooplankton. The copepod community was characterized by low species diversity with Pseudodiaptomus annandalei and Apocyclops royi as main species. Adult copepods and copepodite stages showed total maximum biomass in October and January with 383±35μgCL−1 and 352±74μgCL−1, respectively, where the farmers harvesting effort was minimal. The secondary production, evaluated by the nauplii and copepodites carbon specific growth, was stable at 0.36±0.10d−1 and 0.50±0.05d−1, respectively. The fatty acid composition in the copepods was highly favourable during the winter campaign of which also coincided with a favourable phytoplankton composition. Lastly, this study shows evidence on the yearlong availability of copepods to the pond managers, which, based on standing stock and secondary productivity, easily could improve and intensify their harvest effort. Nauplii could be harvested all year long and adult copepods and copepodites could also be collected during the winter, allowing the pond managers to expand the sales period and thereby increase their revenue.