Search

Aim The so-called regime shifts in North Sea plankton communities provide an important historical case study to understand marine regime shifts. Previous studies characterized regime shifts using a variety of community metrics (e.g., indicator species abundances, taxonomic composition and chlorophyll biomass) but left the functional traits of plankton unassessed. Here, we explicitly re-assess the historically recognized North Sea regime shifts through the lens of plankton functional traits to gain a better understanding of these events. Location The North Sea (NW European shelf). Time period 1958–2018, focusing on the 1980s and 1996–2003 regime shifts. Major taxa studied Marine phyto- and zooplankton. Methods We compute trait spaces for both phyto- and zooplankton of the North Sea using traits from the literature and a Gower's distance-based method. Using abundance data from the Continuous Plankton Recorder Survey, we then compute monthly time series of the centroids of the communities, an indicator of functional composition. We then use principal component analysis on the centroids to assess the main temporal changes in plankton functional composition associated with the 1980s and 1996–2003 regime shifts. Results Little change in plankton functional composition was associated with the 1980s regime shift. In contrast, the functional composition of plankton communities changed markedly after the 1996–2003 regime shift, with an increase in the summer relative abundance of non-motile autotrophs (i.e., diatoms) and the spring relative abundance of meroplankton. Main conclusions The North Sea regime shifts were not associated systematically with changes in functional composition, calling into question the definition of regime shifts and illustrating the importance of taking different metrics into account to interpret ecological events accurately. Taking into account functional composition, we interpret the 1980s so-called regime shift as a latitudinal shift in communities that was insufficient to impact functional composition and the 1996–2003 so-called regime shift as a period of change in bentho-pelagic coupling.

Experimental nutrient additions are a fundamental approach to investigating plankton ecology. Possibilities range from whole-lake fertilization to flask assays encompassing a trade-off between closeness to the “real world” and feasibility and replication. Here we describe an enclosure type that minimizes the manipulation of planktonic communities during the enclosure filling. The enclosure (typically ~100 L volume) consists of a narrow translucent cylinder that can comprise the entire photic zone (or a large part of it in clear deep lakes, e.g. 20-m long) and holds a sediment trap at the bottom for recovering the sinking material. The enclosures are inexpensive and straightforward to build. Thus, many can be used in an experiment, favoring the diversity of treatments and the number of replicates. They also are lightweight with easy transport and use in lakes that cannot be reached by road. The enclosures are fundamentally aimed at investigating the short-term response of the planktonic community, integrated across the photic zone, to pulse perturbations using before and after comparisons and multiple replication and treatments. The pros and cons of the enclosure design are evaluated based on experience gained in Lake Redon, a high mountain ultraoligotrophic deep lake in the Pyrenees.

In a paper entitled The paradox of the plankton , Hutchinson asked 'how it is possible for a number of species to coexist in a relatively isotropic or unstructured environment all competing for the same sorts of materials' (Hutchinson 1961 Am. Nat . 95 , 137–145 ( doi:10.1086/282171 )). Particularly relevant for phytoplankton, this paradox was based on two implicit, and perhaps naive, postulates, i.e. (i) that all plankton species have similar requirements and (ii) that the marine environment is relatively homogeneous in space and time. A number of hypotheses, based on purely theoretical or experimental studies, have been proposed to solve this conundrum, ranging from spatio-temporal environmental heterogeneity to biotic chaotic variability. Here, we characterize the ecological niche of 117 plankton species belonging to three different taxonomic groups and show that all species have a niche sufficiently distinct to ensure coexistence in a structured marine environment. We also provide evidence that pelagic habitats are, unsurprisingly, more diverse in space and time than Hutchinson imagined, the marine environment being neither unstructured nor stable in space and time. We, therefore, conclude that the niche theory, and its corollary the principle of competitive exclusion, apply as much for the plankton as for other forms of life, be they terrestrial or marine.

Many aquatic organisms, including fish, seahorses, clams, and bacteria, depend on plankton because they are an essential component of the aquatic food web. Due to their significance, their distribution in our aquatic environment should be mapped as baseline information. Our new technology aims to create maps of plankton. Our innovative product is called Plankton Map. Our product benefits even more since there is currently no plankton map development, particularly in Malaysia's northern region. In terms of community advantages, Plankton Map will support a wide range of clients, including municipal, governmental, and non-governmental organisations. Overall, Plankton Map is consistent with the Sustainable Development Goals established by the United Nations SDG 14: "Life below water," SDG 2: "Zero hunger," SDG 3: "Good health and well-being," and SDG 13: "Climate action”.

Despite their cosmopolitan occurrence and massive plankton sampling during expeditions, the genetic diversity within Pteropoda Cuvier, 1804 is still largely unexplored. In this study we present a next-generation environmental barcoding approach to zooplankton bulk samples, which were collected during the circumglobal 2010 Malaspina expedition to evaluate pteropod diversity. We introduce a technique that avoids destructive procedures and leaves material intact for further morphological investigations. We extracted DNA out of the dregs (organic material such as mucus or body parts) of 27 sample containers for molecular barcoding (average 100-260 bp of COI). We were able to identify 7128 operational taxonomic units corresponding to the species composition contained in the examined samples. Among them were three species of thecosome pteropods,Creseis acicula,Creseis virgulaandCavolinia inflexa, which are discussed with respect to their taxonomy and their geographic distribution. Unidentified gymnosomes were also present in our samples from warmer regions in oceanic waters of the southern Indian Ocean. To facilitate identification of species, it is beneficial to create a better database of pteropod COI barcodes. Furthermore, gathering environmental barcoding data on a broad global scale will help to better understand species abundance and distribution of pteropods in the world’s oceans, and potentially those of other planktonic organisms., A pesar de su presencia cosmopolita y las actividades de muestreo masivo de plancton durante las expediciones, la diversidad genética dentro de los Pteropoda Cuvier, 1804 está todavía inexplorada en gran medida. En este estudio se presenta una aproximación desde el barcoding ambiental aplicada a muestras generales de zooplancton recogidas durante la expedición circumglobal “Malaspina 2010”, con el fin de evaluar la diversidad de pterópodos. Se introduce una técnica que evita procedimientos destructivos de tal modo que el material permanece intacto para futuras investigaciones morfológicas. Extrajimos ADN de los posos (material orgánico como moco o partes del cuerpo) de 27 recipientes de muestras para el barcoding (promedio de 100- 260 bp de COI). Se pudieron identificar 7128 “OTUs” correspondientes a la composición de las especies contenidas en las muestras examinadas. Entre ellas se encontraron tres especies de pterópodos tecosomados,Creseis acicula,Creseis virgulayCavolinia inflexa, cuya taxonomía y distribución geográfica son discutidas. Gimnosomados no identificados procedentes de regiones más templadas de aguas oceánicas del sur del Océnao Indico también estaban presentes. Para facilitar la identificación de especies, es beneficioso crear una base de datos ampliada de códigos de barras COI de pterópodos. Además, la recopilación de datos de barcoding ambiental a una escala mundial amplia ayudará a comprender mejor la abundancia y distribución de especies de pterópodos en los océanos del mundo y de otros posibles organismos planctónicos.

The effects of lake browning on trophic functioning of planktonic food webs are not fully understood. We studied the effects of browning on the response patterns of polyunsaturated fatty acids and n−3/n−6 ratio in seston and compared them between boreal and temperate lakes. We also compared the regional differences and the effects of lake browning on the reliance of zooplankton on heterotrophic microbial pathways and the mass fractions of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in zooplankton. Lake browning was associated with increasing phytoplankton biomass and concentrations of EPA and DHA in both temperate and boreal lakes, but the seston n−3/n−6 ratio was lower in temperate than boreal lakes, most likely due the differences in phytoplankton community composition. The browning-induced increase in phytoplankton biomass was associated with increased reliance of zooplankton on a heterotrophic microbial pathway for both cladocerans and copepods in boreal and temperate lakes. This increased reliance on the heterotrophic microbial diet was correlated with a decrease in the EPA and DHA mass fractions in temperate copepods and a decrease in the n−3/n−6 ratio in boreal cladocerans and copepods. Our results indicate that although phytoplankton responses to lake browning were similar across regions, this did not directly cascade to the next trophic level, where zooplankton responses were highly taxa- and region-specific. These results indicate that lake browning should be considered as an overarching moderator that is linked to, e.g., nutrient increases, which have more immediate consequences on trophic interactions at the phytoplankton–zooplankton interface.

Breakwater structures made of concrete are used widely around the world, and the bacteria living on these surfaces can cause the concrete to deteriorate. In this study, we collected bacterial biofilms from concrete breakwater structures located along the coast of an island, a mainland coast, and a freshwater riverbank as well as planktonic water samples from each site, and we analysed their bacterial community structures using Illumina sequencing. At the phylum level, Proteobacteria and Actinobacteria dominated planktonic samples, whereas Cyanobacteria, Proteobacteria and Bacteroidetes dominated the biofilm samples. High Cyanobacteria abundance was found in all biofilm samples. Bacterial communities significantly varied between planktonic and biofilm samples and between biofilm samples from seawater and freshwater. Only a small number of bacterial operational taxonomic units were shared by planktonic and biofilm samples from each sampling site. The permanganate index in ambient water had a more significant impact on biofilm bacterial communities than on planktonic samples. Additionally, ammonia nitrogen and total nitrogen contents were positively correlated and salinity was negatively correlated with bacterial beta diversity in biofilm samples.

Aspergillus spp. is the most common clinical pathogen of invasive fungal infection with high mortality. Existing treatments for Aspergillus spp. infection are still inefficient and accompanied by drug resistance, so it is still urgent to find new treatment approaches. The antiarrhythmic drug amiodarone (AMD) has demonstrated antifungal activity against a range of fungi. This study evaluated the efficacy of AMD in combination with triazoles for Aspergillus spp. infection. We tested the combined effect of AMD and three triazole drugs, namely, itraconazole (ITR), voriconazole (VRC), and posaconazole (POS), on the planktonic cells and biofilms of 20 strains of Aspergillus spp. via a checkerboard microdilution assay derived from 96-well plate-based method. Our results reveal that the combination of AMD with ITR or POS against Aspergillus biofilms has synergistic fungicidal effects. By contrast, the combination of AMD with VRC exhibits no antagonistic and synergistic effects. In this way, the use of AMD in combination with ITR or POS could be an effective adjunctive treatment for Aspergillus spp. infection.

Biofilms are communities of bacteria forming high-density sessile colonies. Such a lifestyle comes associated with costs and benefits: while the growth rate of biofilms is often lower than that of their free-living counterparts, this cost is readily repaid once the colony is subjected to antibiotics. Biofilms can grow in antibiotic concentrations a thousand times higher than planktonic bacteria. While numerous mechanisms have been proposed to explain biofilm recalcitrance towards antibiotics, little is yet known about their effect on the evolution of resistance. We synthesize the current understanding of biofilm recalcitrance from a pharmacodynamic and a population genetics perspective. Using the pharmacodynamic framework, we discuss the effects of various mechanisms and show that biofilms can either promote or impede resistance evolution.

The transition from marine to fresh water is a challenging task for juvenile eels. This critical step in the early eels' life is preceded by a metamorphosis from the oceanic larval to the continental glass eel stage, requiring major energy-demanding morphological, physiological and behavioural modifications during which time these animals do not feed. The success of the glass eels' inland migration after metamorphosis will largely depend on remaining energy levels, which can be supplemented only by resuming food uptake. Although it is crucial for their survival and the maintenance of the population, the feeding behaviour of glass eels is still an understudied aspect of the eels' complex life cycle. Many uncertainties about the phenology, diet, potential prey preferences and their relation with migration modus (migratory vs. sedentary) still remain. In this study, the authors analysed the stomach and gut contents of 458 European glass eels (Anguilla anguilla L. 1758) captured in a drainage canal connecting a small mesotidal estuary with an adjacent polder area during the spring migration seasons of 2016 and 2017. They demonstrated that although glass eels started feeding briefly upon arrival in the estuary, food uptake for early arrivals was restricted to a minority that sparsely feed on detritus and some worm-like benthic invertebrates. Along the season, food uptake intensified eventually engaging all glass eels and their dietary palette diversified including a wide array of planktonic and benthic organisms. Crustacean plankton (mainly cyclopoid copepods) was an important part of the glass eel diet, whereas benthic oligochaetes were less abundant as food source in spite of their high presence in the sediments. No clear differences in feeding behaviour could be observed between migratory and sedentary glass eels. This study showed that glass eels can use highly artificial and dynamic drainage canals as feeding ground during their critical marine/freshwater transition. This outcome is also a plea to improve the accessibility of alternative (unnatural) migration routes between the ocean and suitable freshwater growth habitats for the European eel.

This study aimed at performing a systematic review of the literature on the effects of epigallocatechin-3-gallate (EGCG) oniStreptococcus mutans/iplanktonic cultures and biofilms. The selected references demonstrated that EGCG suppressesiS. mutans/iacid production by inhibiting the activity of enzymes such as lactate dehydrogenase and FIF0-ATPase. Regarding virulence factors, one study reported a reduction in soluble and insoluble polysaccharide synthesis, another demonstrated that EGCG inhibited GTase activity, and another showed effects of EGCG on the expression ofigtf/iB, C, and D. The effects of EGCG oniS. mutans/ibiofilms were reported only by 2 of the selected studies. Moreover, high variability in effective concentrations and microbial assessment methods were observed. The literature suggests that EGCG has effects againstiS. mutans/iplanktonic cells viability and virulence factors. However, the literature lacks studies with appropriate biofilm models to evaluate the precise effectiveness of EGCG againstiS. mutans/ibiofilms.

Heavy metals that are adhered to the surfaces of microplastics in the natural marine environment pose potential threats to marine life. However, little is known about their adsorption mechanisms and composite risks. This study collected seawater, suspended particulate matter (SPM), plankton, and microplastic samples from the waters surrounding Hong Kong, established a method for analyzing 13 heavy metals in the plastisphere, and explored the extrinsic and intrinsic sources of the heavy metals by analyzing natural matrices (seawater, SPM, and plankton) and anthropogenic plastics. We found that heavy metals in the plastisphere were significantly affected by the surrounding matrices, as indicated by its positive correlations with the heavy metals in SPM and plankton at most of the sampling sites. Heavy metals in plankton usually occurred as traces of oxides such as As2O3 and ZnO. The partition coefficients of the studied heavy metals between seawater and the plastisphere were identical to those between the SPM and the plastisphere. No correlations were found between the concentrations of heavy metals in the plastisphere and the heavy metal concentrations, masses, quantities, or surface areas of the microplastics, although some polymer types contained extremely high Cd (676 mg/kg), Pb (1,742 mg/kg), and Zn (1,712 mg/kg) concentrations. Only the Cr, Cu, and Ni concentrations were positively correlated with the specific surface area of the microplastics. A cluster analysis showed that Cr, Cu, and Ni were derived from anthropogenic sources, indicating that adventive heavy metals could be adsorbed by plastics with large specific surface areas. We also established a new composite risk assessment method for heavy metals and microplastics that leverages the specific surface areas of microplastics. The assessment results showed that Cd from Tolo Harbor had a strong ecological risk, while As and Cd from the eastern waters off Hong Kong had moderate composite ecological risks.

In recent years, microplastic (MP) pollution has been widely reported. Many studies have shown that MPs in the oceans not only exist in the water but also are eaten by plankton and may be transferred to other trophic levels via the plankton food web. This paper reviews the relationship between MPs and zooplankton, and discusses two aspects of the potential harm of MPs to zooplankton: the effects of MPs on zooplankton ingestion and the influence of MP toxicity on zooplankton. MPs are often eaten by zooplankton because they resemble prey in size, color, and buoyancy. Zooplankton ingest MPs directly or indirectly, resulting in intestinal damage, reduced ingestion, slow or delayed growth, reduced spawning, shortened lifespan, and abnormal or even fatal gene expression. MP ingestion by zooplankton also affects their behavior, reproduction, and offspring. MPs constitute an uncertain threat to zooplankton. Integration of MPs into the zooplankton community affects filtering organisms feeding. The mechanism of MP toxicity in zooplankton is not yet fully understood and more studies are needed.

Biofilms are the oldest, most successful, and most widely distributed form of microorganism life on earth, existing even in extreme environments. Presently, probiotics in biofilm phenotype are thought as the most advanced fourth-generation probiotics. However, high-efficiency and large-scale biofilm enrichment in an artificial way is difficult. Here, fibrous membranes as probiotic biofilm-enriching materials are studied. Electrospun cellulose acetate nanofibrous membranes with nano-sized fibers show outstanding superiority over fibrous membranes with micron-sized fibers in

Two nutrient–phytoplankton–zooplankton (NZP) models for a closed ecosystem that incorporates a delay in nutrient recycling, obtained using the gamma distribution function with one or two degrees of freedom, are analysed. The models are described by systems of ordinary differential equations of four and five dimensions. The purpose of this study is to investigate how the mean delay of the distribution and the total nutrients affect the stability of the equilibrium solutions. Local stability theory and bifurcation theory are used to determine the long-time dynamics of the models. It is found that both models exhibit comparable qualitative dynamics. There are a maximum of three equilibrium points in each of the two models, and at most one of them is locally asymptotically stable. The change of stability from one equilibrium to another takes place through a transcritical bifurcation. In some hypotheses on the functional response, the nutrient–phytoplankton–zooplankton equilibrium loses stability via a supercritical Hopf bifurcation, causing the apparition of a stable limit cycle. The way in which the results are consistent with prior research and how they extend them is discussed. Finally, various application-related consequences of the results of the theoretical study are deduced.

The United Nations has declared 2021-2030 the Decade of Ocean Science for Sustainable Development; increasing ocean literacy is an integral part of the larger network of actions intended to address the numerous environmental crises the global ocean faces. Many aspects of Ocean science remain opaque to the public, including the world of planktonic organisms. The arts provide an expansive laboratory for communicating and interacting with scientific topics, including in modes that engage visual and kinesthetic learners. I designed an interactive artinstallation and STEAM lesson plan for elementary students, with the intention of creating a somatic mode to engage with complex topics in biological oceanography. The topic was biological-physical interactions with plankton, with a focus on turbulence, based on the research of Scripps Institution of Oceanography Professor Peter Franks. Prototypes of the art installation “Plankterception” were exhibited at two events at the Birch Aquarium, where the public interacted with the work and engaged with the scientific material through conversations with me and accessing an informative website. The lesson plan was distributed to elementary school teachers in the San Diego Unified School District as a resource to celebrate World Oceans Day, using drawing and dance as a tool to think critically about plankton physiology.See website created for this project here:https://www.plankterception.com/

It is generally assumed that viruses outnumber cells on Earth by at least tenfold. Virus-to-microbe ratios (VMR) are largely based on counts of fluorescently labelled virus-like particles. However, these exclude intracellular viruses and potentially include false positives (DNA-containing vesicles, gene-transfer agents, unspecifically stained inert particles). Here, we develop a metagenome-based VMR estimate (mVRM) that accounts for DNA viruses across all stages of their replication cycles (virion, intracellular lytic and lysogenic) by using normalised RPKM (reads per kilobase of gene sequence per million of mapped metagenome reads) counts of the major capsid protein (MCP) genes and cellular universal single-copy genes (USCGs) as proxies for virus and cell counts, respectively. After benchmarking this strategy using mock metagenomes with increasing VMR, we inferred mVMR across different biomes. To properly estimate mVMR in aquatic ecosystems, we generated metagenomes from co-occurring cellular and viral fractions (>50 kDa-200 µm size-range) in freshwater, seawater and solar saltern ponds (10 metagenomes, 2 control metaviromes). Viruses outnumbered cells in freshwater by ∼13 fold and in plankton from marine and saline waters by ∼2-4 fold. However, across an additional set of 121 diverse non-aquatic metagenomes including microbial mats, microbialites, soils, freshwater and marine sediments and metazoan-associated microbiomes, viruses, on average, outnumbered cells by barely two-fold. Although viruses likely are the most diverse biological entities on Earth, their global numbers might be closer to those of cells than previously estimated.

Vibrio is ubiquitous in marine environments with high metabolism flexibility and genome plasticity. Studies have investigated the ecological distribution of Vibrio spp. in several narrow zones, but a broad scale pattern of distribution and community assembly is still lacking. Here, we elucidated the distribution of Vibrio spp. in seawater along the Chinese marginal seas with a high spatial range. Comparison of Vibrio abundance between 3- and 0.2-μm-pore-size membranes showed distinction in preferential lifestyle. Vibrio spp. in the Yellow Sea (YS) was low in abundance and adopted a particle-associated lifestyle, whereas that in the East China Sea (ECS) and South China Sea (SCS) was more abundant and was likely in a temporary free-living state as a strategy to cope with nutrient limitation. Vibrio community compositions were also separated by sampling area, with different dominant groups in YS (Vibrio chagasii and Vibrio harveyi), ECS and SCS (Vibrio japonicus and V. chagasii). The community niche breadth was significantly wider in ECS and SCS than that of YS. Among species, V. chagasii and V. harveyi had the largest niche breadths likely reflecting strong competitive positions. Stochastic processes played important roles in shaping the geographical pattern of the vibrionic community. Environmental selection (e.g., temperature, salinity, and dissolved oxygen) had a much greater impact on the community in surface than in bottom water. The large proportions of unexplained variations (78.9%) imply complex mechanisms in their community assembly. Our study provides insights into the spatial distribution patterns and underlying assembly mechanisms of Vibrio at a broad spatial scale. IMPORTANCE Vibrio spp. may exert large impacts on biogeochemical cycling in coastal habitats, and their ecological importance has drawn increasing attention. Here, we investigated the spatial distribution pattern and community assembly of Vibrio populations along the Chinese marginal seas, spanning a wide spatial scale. Our results showed that the abundances of the Vibrio population increased with decreasing latitude and their preferential lifestyle differed among adjacent coastal areas. The compositions of Vibrio spp. were also separated by geographical location, which was mainly attributable to stochastic processes. Overall, this work contributes to the understanding of the ecological distribution patterns and the community assembly mechanisms of marine vibrios at a high spatial range. The large proportion of unexplained variations indicates the existence of complex mechanisms in the assembly of vibrionic community which should be considered comprehensively in future.

Chemotaxonomic biomarkers are needed to monitor and evaluate the nutritional quality of phytoplankton communities. The biomolecules produced by different phytoplankton species do not always follow genetic phylogeny. Therefore, we analyzed fatty acids, sterols, and carotenoids from 57 freshwater phytoplankton strains to evaluate the usability of these biomolecules as chemotaxonomic biomarkers. We found 29 fatty acids, 34 sterols, and 26 carotenoids in our samples. The strains were grouped into cryptomonads, cyanobacteria, diatoms, dinoflagellates, golden algae, green algae, and raphidophytes, and the phytoplankton group explained 61%, 54%, and 89% of the variability of fatty acids, sterols, and carotenoids, respectively. Fatty acid and carotenoid profiles distinguished most phytoplankton groups, but not flawlessly. For example, fatty acids could not distinguish golden algae and cryptomonads, whereas carotenoids did not separate diatoms and golden algae. The sterol composition was heterogeneous but seemed to be useful for distinguishing different genera within a phytoplankton group. The chemotaxonomy biomarkers yielded optimal genetic phylogeny when the fatty acids, sterols, and carotenoids were used together in multivariate statistical analysis. Our results suggest that the accuracy of phytoplankton composition modeling could be enhanced by combining these three biomolecule groups.

The northern coast of the Iberian Peninsula is an important spawning and nursery area for several marine fish species, some of which are economically exploited by fisheries and under management plans. Larval stages of fish are highly sensitive to environmental change and anthropogenic pressures, and Marine Protected Areas (MPA) can help mitigate the impacts on fish populations. This study investigated the environmental drivers of the temporal and spatial patterns of the larval fish assemblages inhabiting a small coastal MPA along the NW Portuguese Iberian Coast. Seasonal surveys were conducted over two years at nine sampling stations distributed throughout the MPA to collect larval fish samples and water parameters. Results showed that a total of 39 different fish taxa were identified. In terms of abundance, reef-associated species, such as Parablennius gattorugine (54.6%), and marine species that use estuaries as nursery areas, such as Ammodytes tobianus (15.7%) and Clupeidae n.i. (8.8%) dominated the larval fish assemblages. The larval fish assemblages were characterized by a strong temporal pattern that, according to CCA analyses, was related to the temporal variability of water temperature, pH, chlorophyll α, TPM, and also the river flow of an adjacent river. This study showed that 47% of the fish larvae belonged to commercially exploited species, highlighting the importance of this MPA as a nursery area for the early life stages of the fish population. Overall, these new findings emphasize the role of MPAs in ensuring the connectivity of fish species between marine-estuarine habitats and enhancing the conservation of fish populations.

Litopenaeus vannamei is one of the largest commodities having a major impact on the global economy. Shrimp larvae have drastic changes in morphology and physiology which require extra maintenance. Feed management in early rearing using a blind feeding system which plankton as the main food. The relation between plankton and C/N needs to be investigated to optimize the growth of natural feed. The aims of the study were to analyze plankton community structure; the relationship between plankton to C/N and the environmental parameters; and determine the shrimp preferences of plankton. Data were collected at 3 points in 3 different ponds (PA, PB, PC) on day 8 and day 15 using a stratified sampling method with criteria (intensive system and blind feeding phase). Plankton density and C/N relationship were analyzed using Linear Regression, plankton and environmental parameters using Canonical Correspondence Analysis (CCA). Shrimp food preferences were analyzed descriptively in percentage. The results showed that diatoms and dinoflagellates dominated phytoplankton, and rotifers dominate zooplankton. C/N showed a positive correlation to protozoa, but a negative correlation to pennate diatoms and copepods. The most influential environmental factors for both phytoplankton and zooplankton density were temperature, C-organic, salinity, pH, alkalinity, and dissolved oxygen.

International audience; This paper looks at experiential feedback and the technical and scientific challenges tied to the MERITE-HIPPOCAMPE cruise that took place in the Mediterranean Sea in spring 2019. This cruise proposes an innovative approach to investigate the accumulation and transfer of inorganic and organic contaminants within the planktonic food webs. We present detailed information on how the cruise worked, including 1) the cruise track and sampling stations, 2) the overall strategy, based mainly on the collection of plankton, suspended particles and water at the deep chlorophyll maximum, and the separation of these particles and planktonic organisms into various size fractions, as well as the collection of atmospheric deposition, 3) the operations performed and material used at each station, and 4) the sequence of operations and main parameters analysed. The paper also provides the main environmental conditions that were prevailing during the campaign. Lastly, we present the types of articles produced based on work completed by the cruise that are part of this special issue.

Paleontological reconstructions of plankton community structure during warm periods of the Cenozoic (last 66 million years) reveal that deep-dwelling 'twilight zone' (200-1000 m) plankton were less abundant and diverse, and lived much closer to the surface, than in colder, more recent climates. We suggest that this is a consequence of temperature's role in controlling the rate that sinking organic matter is broken down and metabolized by bacteria, a process that occurs faster at warmer temperatures. In a warmer ocean, a smaller fraction of organic matter reaches the ocean interior, affecting food supply and dissolved oxygen availability at depth. Using an Earth system model that has been evaluated against paleo observations, we illustrate how anthropogenic warming may impact future carbon cycling and twilight zone ecology. Our findings suggest that significant changes are already underway, and without strong emissions mitigation, widespread ecological disruption in the twilight zone is likely by 2100, with effects spanning millennia thereafter.

The early–middle Frasnian boundary interval of the northern part of the East European Platform (northwest of Russia) corresponding to the transitans-punctata isotope event is revealed by biostratigraphically constrained conodont carbon stable isotope data (δ13Ccon). The dynamics of δ13Ccon demonstrate a three-fold pattern with positive peaks at the onset of the main phase of the transitans-punctata isotope event (upper part of Montagne Noire 4 conodont Zone, MN4; up to -22.5‰ VPDB), and during the late part of the event (lower and middle parts of MN6 Zone; up to -24.0‰ VPDB and -22.1‰ VPDB). The stratigraphic level near the MN5 and MN6 boundary is marked by a prominent negative excursion in δ13Ccon (down to -31.8‰ VPDB) that resembles the negative excursion in the terminal phase of the transitans-punctata isotope event worldwide. The δ13Ccon variations in different taxa are generally consistent but demonstrate some differences in values and amplitudes. It is assumed that variations in the carbon isotopic compositions of conodonts were mainly controlled by changes in the isotope composition of the planktons as the main food source for conodonts.

Microplastics, i.e., plastic particles in the size range of planktonic organisms, have been found in the water columns and sediments of lakes and rivers globally. The number and mass of plastic particles drifting through a river can exceed those of living organisms such as zooplankton and fish larvae. In freshwater sediments, concentrations of microplastics reach the same magnitude as in the world’s most contaminated marine sediments. Such particles are derived from a unique biogeochemical cycle that ultimately influences productivity, biodiversity, and ecosystem functioning. Furthermore, microplastics act as vectors of toxic substances to invertebrates, fishes, herpetofauna, and waterfowl. We contend that the concentration of this distinct particle component is an ecologically significant parameter of inland waterbodies because of its ubiquity, environmental persistence, and interactions with key ecological processes. No environmental field survey that has searched for microplastics has yet failed to detect their presence. Standardized limnological protocols are needed to compare spatio-temporal variation in the concentration of microplastics within and across watersheds. Data obtained from such protocols would facilitate environmental monitoring and inform policy for managing plastic waste; furthermore, they would enable more accurate modeling of contaminant cycling and the development of a global plastic budget that identifies sources, distribution and circulation pathways, reservoir size, and retention times.

Nosocomial bacterial infections associated with biofilms inspire to explore newer bactericidal strategy with eco-friendly biomaterials as sustainable alternatives. In this research work, we successfully developed bio-safe films from kojic acid(KA) and guar gum propionate(GGP) for Escherichia coli biofilm disruption and planktonic cell killing. High DS(degree of substitution = 1.52) GGP was synthesized from guar gum (GG)assisted by chaotropic ions at room-temperature. Biopolymers were routinely characterized in CHN analyzer, FT-IR, TGA and XRD analysis. KA loaded GGP films were prepared by cross-linking the molecules in presence of epichlorhydrin and two different percentages of KA were employed. Film physical and tensile properties were systematically evaluated and optimized. Water vapour permeability (WVP) and tensile strength of final film GGPFK10 were recorded at 0.741 ± 0.09gmm

Providencia rettgeri is an opportunistic foodborne pathogen with a strong biofilm-forming ability in low-nutrition environments. However, information regarding the impact of simulated food processing conditions on P. rettgeri planktonic growth and biofilm formation is limited. Using response surface methodology (RSM), the combined effects of temperature (19 to 37°C), pH (5 to 9), and sodium chloride (NaCl) concentration (0.50 to 2.0%, w/v) were applied to construct planktonic growth and biofilm formation models for P. rettgeri. For both RSM models, an increase in NaCl concentration restricted P. rettgeri growth. Planktonic growth and biofilm formation were maximum at 27.83 and 25.41°C, respectively. Tannic acid (TA) is a highly effective antibacterial agent that inhibited planktonic and biofilm P. rettgeri under optimal growth conditions. The viability of P. rettgeri cells was decreased by TA treatment, which caused destruction of the cell membrane and production of endogenous reactive oxygen species. TA significantly inactivated P. rettgeri biofilms, as verified by observation. The obtained models in this study may be useful for describing the impact of temperature, pH, and NaCl concentration on the growth by P. rettgeri in the food processing environment and better understanding the impacts of food-related conditions on bacterial planktonic growth and biofilm formation. These results obtained for P. rettgeri planktonic cells and biofilms can provide a framework for removal strategies for other foodborne pathogens.

Planktonic copepods are the most abundant animals in the ocean and key players in global biochemical processes. Recent modeling suggests that zooplankton ingestion of microplastics (MPs) can disrupt the biological carbon pump and accelerate a global loss of oceanic oxygen. Here we investigate the behavioral responses and ingestion rates of a model feeding-current generating copepod when exposed to microplastics of different characteristics by small-scale video observations and bottle incubations. We found that copepods rejected 80% of the microplastics after touching them with their mouth parts, in essence exhibiting a kind of taste discrimination. High rejection rates of microplastics were independent of polymer type, shape, presence of biofilms, or sorbed pollutant (pyrene), indicating that microplastics are unpalatable for feeding-current feeding copepods and that post-capture taste discrimination is a main sensorial mechanism in the rejection of microplastics. In an ecological context, taking into account the behaviors of planktonic copepods and the concentrations of microplastics found in marine waters, our results suggest a low risk of microplastic ingestion by zooplankton and a low impact of microplastics on the vertical exportation of fecal pellets.

Salinity is a major environmental predictor of phytoplankton species richness and composition. We hypothesize that the variation in phytoplankton richness along coastal salinity gradients is reflected in essential ecosystem functions like resource use efficiency (RUE)—the proportion of limiting resource that is converted into biomass. To test the hypothesis, we analyzed time series of phytoplankton and environmental variables from the Chesapeake Bay and the Baltic Sea. We analyzed the relationship among salinity, diversity, and RUE in bivariate and interaction association, and in structural equation model (SEM)—a form of path analysis to resolve multivariate relationships among interrelated variables. We concluded that the intrusion of marine water will lead to rapid change in species diversity on the fresh side. Despite diversity drop, individual community functions, like RUE, remain relatively resilient, reflecting functional redundancy. We propose that the salinity gradient also reflects trophic complexity, allowing stable resource use at reduced diversity. Scientific Significance Statement Most functional groups of aquatic organisms have a diversity minimum at intermediate salinity along the coastal and estuarine gradient. As ecosystem functioning scales with biotic diversity, we hypothesized the salinity gradient to be a good predictor of ecosystem functions. We found that phytoplankton resource use efficiency—an essential ecosystem function—was relatively stable along the salinity gradient reflecting functional redundancy, and the salinity effect was mediated by diversity. We suggest that salinity reflects also a gradient in trophic complexity, allowing stable resource use at reduced diversity.

Although marine ecosystem is a highly complex phenomena with many non-linearly interacting species, dissolved oxygen and plankton among these have perhaps the most fundamental relationship not only for the protection of marine environment but also for continuation of life on Earth. This paper deals with a generic diffusive model of dissolved oxygen, phytoplankton and zooplankton species, for which constant time delays are incorporated in growth response of phytoplankton and in the gestation time of zooplankton. We mainly focus on the stability analysis of the coexisting states and the existence of Hopf bifurcation through the characteristic equation, where time delay and oxygen production rate are considered as control parameters for all cases. Studying the effect of both time delays on a stable system, we show destabilisation of the system and irregularity in the spatio-temporal dynamical regimes, leading to chaotic oscillations. Although both delay terms have a destabilising effect, our findings indicate that time delay in zooplankton gestation may induce sharp strongly irregular pattern, whereas time delay in phytoplankton growth gives rise to more regular but higher frequency oscillations for oxygen-plankton interactions. The findings of this paper may provide new insights into main environmental issues including global warming and climate change.

It is well-established that environmental variability and cyanobacterial blooms have major effects on the assembly and functioning of bacterial communities in both marine and freshwater habitats. It remains unclear, however, how the ciliate community responds to such changes over the long-term, particularly in subtropical lake and reservoir ecosystems. We analysed 9-year planktonic ciliate data series from the surface water of two subtropical reservoirs to elucidate the role of cyanobacterial bloom and environmental variabilities on the ciliate temporal dynamics. We identified five distinct periods of cyanobacterial succession in both reservoirs. Using multiple time-scale analyses, we found that the interannual variability of ciliate communities was more strongly related to cyanobacterial blooms than to other environmental variables or to seasonality. Moreover, the percentage of species turnover across cyanobacterial bloom and non-bloom periods increased significantly with time over the 9-year period. Phylogenetic analyses further indicated that 84 %–86 % of ciliate community turnover was governed by stochastic dispersal limitation or undominated processes, suggesting that the ciliate communities in subtropical reservoirs were mainly controlled by neutral processes. However, short-term blooms increased the selection pressure and drove 30 %–53 % of the ciliate community turnover. We found that the ciliate community composition was influenced by environmental conditions with nutrients, cyanobacterial biomass and microzooplankton having direct and/or indirect significant effects on the ciliate taxonomic or functional community dynamics. Our results provide new insights into the long-term temporal dynamics of planktonic ciliate communities under cyanobacterial bloom disturbance.

Runoff containing road salt (sodium chloride, NaCl) causes the salinization of inland freshwaters, with potentially severe impacts on aquatic species. We performed a mesocosm experiment to test the effects of salinization on plankton community structure in an oligotrophic mountain lake with a limited history of elevated salt concentrations. We exposed plankton communities to a gradient of 30 salt concentrations ranging from 1 to 2900 Cl− mg L−1 for 6 weeks. Adding salt increased zooplankton biomass at concentrations < 500 mg Cl− L−1 while reducing phytoplankton biomass. Zooplankton biomass declined precipitously at higher concentrations, with phytoplankton biomass showing a mirror image increase. The initial increase in zooplankton biomass with salt addition suggests that zooplankton are salt-limited at low ionic concentrations. Additionally, the inverse response of zooplankton and phytoplankton suggests that salinity mainly affects phytoplankton biomass via changes in top-down regulation by grazers.

The self-binding of bacterial cells, or autoaggregation, is, together with surface colonization, one of the first steps in the formation of a mature biofilm. In this work, the autoaggregation of B. subtilis in dilute bacterial suspensions was studied. The dynamics of cell lysis, eDNA release, and bacterial autoaggregate assembly were determined and related to the spatial autocorrelation of bacterial cells in dilute planktonic bacterial suspensions. The non-random distribution of cells was associated with an eDNA network, which stabilized the initial bacterial cell-cell aggregates. Upon the addition of DNase I, the aggregates were dispersed. The release of eDNA during cell lysis allows for the entrapment of bacterial drifters at a radius several times the size of the dying bacteria. The size of bacterial aggregates increased from 2 to about 100 μm in diameter in dilute bacterial suspensions. The results suggest that B. subtilis cells form previously unnoticed continuum of autoaggregate structures during planktonic growth.

Within the marine fossil record, size is a fundamental trait providing information on both assemblages and individual species. Changes in size within an assemblage are largely driven by species composition typically related to environmental conditions. Changes in size of an individual species can be an indicator of health and whether optimal growth conditions (i.e. temperature, salinity and food availability) prevail. Over evolutionary timescales, individuals tend to increase in size (Cope’s rule) also altering the average size of the population.The Pliocene provides an excellent opportunity to look at environmental drivers and ecological responses to a warmer world, at high resolution and with extant species. A short glaciation phase, during marine isotope stage (MIS) M2, interrupted the Pliocene global warming between ~ 3.31 – 3.26 Ma. This event provides the ideal framework to quantify how biota, already adapted to warming conditions, respond to a short, but substantial cooling event. We analysed the size and species composition of samples collected as part of the Pliocene Research, Interpretation and Synoptic Mapping (PRISM) Project from a variety of locations around the globe. The samples cover the Atlantic, Indian and Pacific oceans at a range of latitudes (e.g. DSDP Site 521, 586, 607 and ODP Site 716, 754, 887). We measured the maximum diameter of planktonic foraminifera tests with a fully automated light microscope, enabling high resolution sampling at a multitude of sites, before, during and after the MIS M2 glaciation event. On average 2000 specimens were measured per sample, resulting in over a million analyses in total. Changes in planktonic foraminiferal assemblage composition were characterised by quantifying relative species abundances and augmented by determining the largest species.Planktonic foraminiferal assemblage size shows a general increase during the Pliocene likely related to warming temperatures. What is unclear is if this change is driven by changes in diversity due to extinction and origination, responses to environmental change or a general increase in size of species found through the record. Here we discuss reactions of species and (or) ecological groups to environmental change and determine the individual drivers of size change across the world’s oceans.

Unidad de excelencia María de Maeztu CEX2019-000940-M Thecosome pteropods are a dominant group of calcifying pelagic molluscs and an important component of the food web. In this study, we characterise spring pteropod distribution throughout the Mediterranean Sea, an understudied region for this common group of marine calcifying organisms. This semi-enclosed sea is rapidly changing under climatic and anthropogenic forcings. The presence of surface water biogeochemical gradients from the Atlantic Ocean/Gibraltar Strait to the Eastern Mediterranean Sea allowed us to investigate pteropod distribution and their ecological preferences. In the ultra-oligotrophic Eastern Mediterranean Sea, we found the mean upper 200 m pteropod standing stock of 2.13 ind. m−3 was approximately 5x greater than the Western basin (mean 0.42 ind. m−3). Where standing stocks were high, pteropods appeared largely in the same family grouping belonging to Limacinidae. Temperature, O2 concentration, salinity, and aragonite saturation (Ωar) explain 96 % of the observed variations in the communitystructure at the time of sampling, suggesting that pteropods might show a preference for environmental conditions with a lower energetic physiological demand. We also document that pteropods and planktonic foraminifera have an opposite geographical distribution in the Mediterranean Sea. Our findings indicate that in specific pelagic ultra-oligotrophic conditions, such as the Eastern Mediterranean Sea, different feeding strategies could play an important role in regulating calcifying zooplankton distribution.

Fish introduction into fishless high-altitude lakes has detrimental effects on biodiversity. Removal of alien fish through intensive fishing is cost-intensive and difficult to achieve in productive lakes. Lake Sulzkarsee is the only lake in the National Park Gesäuse, Austria, and was an important breeding site for amphibians until the lake was stocked with fish in the late 1970s. Salmonids were eradicated in 2005, but the lake remained degraded by the introduced minnows (Phoxinus sp.). In 2018, the lake was drained through a siphon pipe and then by pumping out water with dirt water pumps. The deepest part was treated with slaked lime, but several hundred adult minnows survived in sediment crevices and reproduced in the following season. After drainage, the phytoplankton biomass increased. Indicator species, such as Daphnia longispina and amphibians, showed signs of recovery, but they went back to an impacted state when minnows recovered after the failed eradication attempt. Purse seines proved to be the most efficient gear to catch minnows. These results indicate that deep mountain lakes are difficult to drain efficiently. Sediment treatment is required to eliminate all fish.

Murray-Darling Freshwater Research CentreMDFRC item.1. Contrary to that for lakes and ponds, our knowledge of the influence of planktivorous fish on zooplankton communities in rivers is slight, largely because of the general assumption that such communities are overwhelmingly regulated by physical conditions. 2. In two separate but concurrent in situ enclosure experiments, we investigated the effects of carp gudgeon (Hypseleotris spp.) and Eastern Gambusia (Gambusia holbrooki) on zooplankton communities in slackwaters of a temperate Australian floodplain river. 3. A high biomass of Hypseleotris suppressed the density of daphniid microcrustaceans, but enhanced the total density of rotifers. A high biomass of Gambusia, on the other hand, suppressed the total density of both microcrustaceans and rotifers. 4. A high biomass of planktivorous fish also reduced the density of many of the ovigerous (egg-carrying) zooplanktonic taxa. Indeed, ovigerous cyclopoid copepods were suppressed in the presence of a high biomass of Hypseleotris, even though there was no significant effect on overall (ovigerous plus non-ovigerous) density. 5. Our results imply that a high biomass of planktivorous fish can potentially influence zooplankton communities in riverine slackwaters, as in many lakes and ponds.

Murray-Darling Freshwater Research CentreMDFRC item.Planktivorous fish are important in shaping zooplankton communities in many freshwater ecosystems, and there is an intrinsic link between the active and resting forms of many zooplankton taxa. However, few field studies have considered the influence of planktivorous fish on zooplankton resting-stage communities, and none have considered this phenomenon in rivers. In two separate but concurrent 12-day experiments, we investigated the effects of Eastern Gambusia (Gambusia holbrooki Girard) and carp gudgeon (Hypseleotris spp.) on zooplankton resting-stage communities in slackwaters of an Australian floodplain river. This was achieved by setting coconut fibre mats on the bottom of the experimental enclosures and later incubating the resting stages captured. A high biomass (2.5 g m(-2)) of Gambusia suppressed the total abundance and diversity of resting-stage microcrustaceans between days 6 and 12, and the abundance of resting-stage Asplanchna spp. throughout the entire 12-day period. Furthermore, a high biomass of Hypseleotris suppressed the total diversity of resting-stage rotifers between days 0 and 6. These response patterns generally reflected changes in active populations according to the fish biomass treatment, rather than changes in dormancy induction by active individuals. This suggests that a high biomass of planktivorous fish can potentially influence zooplankton resting-stage communities in riverine slackwaters in addition to active zooplankton communities due to the inherent association between resting stage and active forms of zooplankton taxa.

Temperature increases driven by climate change are expected to decrease the availability of polyunsaturated fatty acids in lakes worldwide. Nevertheless, a comprehensive understanding of the joint effects of lake trophic status, nutrient dynamics and warming on the availability of these biomolecules is lacking. Here, we conducted a laboratory experiment to study how warming (18–23°C) interacts with phosphorus (0.65–2.58 μM) to affect phytoplankton growth and their production of polyunsaturated fatty acids. We included 10 species belonging to the groups diatoms, golden algae, cyanobacteria, green algae, cryptophytes and dinoflagellates. Our results show that both temperature and phosphorus will boost phytoplankton growth, especially stimulating certain cyanobacteria species (Microcystis sp.). Temperature and phosphorus had opposing effects on polyunsaturated fatty acid proportion, but responses are largely dependent on species. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) synthesizing species did not clearly support the idea that warming decreases the production or content of these essential polyunsaturated fatty acids. Our results suggest that warming may have different effects on the polyunsaturated fatty acid availability in lakes with different nutrient levels, and that different species within the same phytoplankton group can have contrasting responses to warming. Therefore, we conclude that future production of EPA and DHA is mainly determined by species composition. peerReviewed

International audience; Despite concern around plastic pollution in subtropical gyres, our understanding of the biological component of the neustonic layer (upper 20 cm of the ocean) in these areas is poor. Here we investigate the neuston (excluding copepods) assemblages across the Southern Indian Subtropical Gyre using triplicate samples collected by manta-trawls from 28 stations along a transect at latitude 20 S during June/July 2015. The vertical structure of the water column at each station was assessed using a CTD. With the exception of siphonophores, all non-copepod neuston were identified to morphospecies. Assemblages were dominated by ostracods, mysids, larval chaetognaths and siphonophores. The majority of collected specimens comprised facultative neuston, which were more common at night than during the day. Neuston assemblages from the east were quite distinct from the balance of samples, and their distribution reflected that of the warm, low salinity water associated with the Indonesian Throughflow. Two anticyclonic eddies had been documented at the time of the survey between 70 and 85° E, and this area was associated with a distinct neuston assemblage of generally low abundance. The key environmental factors that were linked to assemblage structure were associated with longitude - salinity, fluorescence and temperature at 200 m, emphasising the interaction between Indonesian Throughflow Water and the South Equatorial Current, eddy-related process and settlement of meroplankton. The study highlights the value of using morphospecies in studies of plankton assemblages.

La Trobe University Faculty of Science, Technology and Engineering Murray Darling Freshwater Research CentreMDFRC item.Bacterial production is important in aquatic carbon cycles because it represents a key component whereby dissolved and particulate carbon can be recycled back into food webs. Despite its acknowledged importance, few studies have examined bacterial production in lowland rivers. Since studies have suggested bacterial production is closely related to some carbon pools, we anticipated this to be the case in the Murray River, but that the timing and type of carbon inputs in the Murray River may lead to bacterial dynamics that differ from studies from other sites. Bacterial abundance and production were measured at three contrasting sites of the lowland Murray River, southeastern Australia, over an 18- month period. Bacterial abundance varied across the three sites on the Murray River and was correlated with chlorophyll a concentrations but not with temperature, nutrients, particulate organic carbon and dissolved organic carbon concentrations. Bacterial production also varied across the sites. Lowest production was at the site most immediately downstream of a large reservoir, with production generally ranging from 0.88 to 8.00 mu g CL-1 h(-1). Bacterial production in a reach within a large forest ranged from 4.00 to 17.38 mu CL-1 h(-1). Production at the reach furthest downstream ranged from 1.04 to 23.50 mu g C L-1 h(-1). Bacterial production in the Murray River was generally greater than in the European River Spree, reaches of the Meuse and Rhine without immediate impacts from major urban centres and the Amazon River, but was similar to the concentration measured in the Mississippi and Hudson Rivers. Bacterial production was closely correlated with chlorophyll a concentration and total phosphorus, but not with temperature, dissolved organic carbon, particulate organic carbon or inorganic nitrogen. Despite the differences in production and respiration measured at different sites across the Murray River, bacterial growth efficiency was very similar at the three sites. Bacterial populations in the Murray River appear to be influenced by reach-specific conditions rather than broad-scale drivers such as temperature, carbon and nutrient concentrations.

Flysch marks the synorogenic deposition in external foreland fold-and-thrust belts (FATB) around the globe. Thus, a precise estimation of its stratigraphic range is crucial for reconstructing the orogenic histories in these belts. Dinarides FATB is a young orogen settled between the Alps and the Hellenides in SE Europe originating from the NE-wards subduction of the Adriatic plate under the Eurasia. The youngest onshore flysch deposits termed the Dalmatian Flysch mark the position of the External Dinarides foreland basin (EDFB) stretching both over its interior High Karst as well as its exterior Dalmatian tectonic unit. There is an ongoing discussion on its stratigraphic context, contrasting a Paleogene with a Neogene age. Such a difference in age estimation provides severe uncertainties for the reconstruction of tectonic and paleogeographic constrains. In particular, the Neogene age of the Dalmatian Flysch would imply the coexistence of contractional and extensional tectonics in the Miocene of External Dinarides ; the latter marked by establishment of numerous intramountain basins encompassing a long lasting lacustrine environment of the so-called Dinarides Lake System. To test the hypothesis on such coexistence, 76 sediment bulk-samples have been collected from 31 sites of the Dalmatian Flysch referred to by current literature as Miocene. They are distributed along a 400-km-long axial transect of the EDFB in Croatia, Bosnia–Herzegovina, and Montenegro between cities of Pag in the NW and Ulcinj in the SE. In contrast to previous studies, we use the calcareous plankton stratigraphy integrating nannoplankton and foraminifera records. Our preliminary results detected neither the presence of Miocene, nor of Oligocene assemblages in the samples. This result is supported by the occurrence of well-preserved planktonic foraminifera including the Middle to Late Eocene stratigraphic markers Globigerinatheka barri, Hantkenina compressa, and Morozovelloides crassatus. The corresponding stratigraphic interval is corroborated by the calcareous nannoplankton assemblages comprising index species such as Sphenolithus furcatolithoides, Cribrocentrum reticulatum, C. erbae, and Furcatolithus obtusus. Accordingly, the present data prove a marine offshore deposition in the EDFB during the Oligocene and the Miocene improbable.

Murray-Darling Freshwater Research CentreMDFRC item.

La Trobe University Faculty of Science, Technology and Engineering Murray Darling Freshwater Research CentreMDFRC item.Microfaunal samples were collected from within the channels of three rivers in north eastern Victoria, Australia (the Murray, Ovens and Broken Rivers) as a component of a study examining the effects of flow on the biota of lowland rivers in Australia. Samples were collected from the water column of the river channel and slackwaters and from the layer of water immediately above the bottom sediment of the slackwaters. There was no connectivity between the river channel and the floodplain wetlands for all three rivers during the sampling period. Substantial numbers of microfauna were resident in the slackwaters of all three rivers, with the greatest densities occurring close to the bottom sediment, with densities often exceeding 1000 animals l−1 whereas in the plankton samples densities were usually less than 500 animals l−1. The presence of large and diverse microfaunal communities and the lack of connectivity between the river channel and associated floodplain wetland indicate that these communities are capable of persisting and recruiting within riverine channel slackwaters.

The early Cambrian Buen Formation of North Greenland is celebrated for hosting one of the oldest Cambrian Burgess Shale-type deposits known to date – the Sirius Passet Lagerstätte. Further south in a shallower shelf facies belt, the Buen Formation yielded organic-walled microfossils (OWMs) that were originally described with a focus on acritarchs. Later sampling revealed a diversity of small carbonaceous fossils (SCFs) of metazoan origin. This PhD thesis investigates the diversity of OWMs from the Buen Formation using a novel combination of approaches. First, new samples are processed using a gentle acid maceration protocol designed for the recovery of large, delicate elements. Second, a population-based analysis of disparity is conducted to evaluate acritarch diversity, and illuminate the poorly known palaeobiology of these microfossils. New sampling revealed a remarkable diversity of metazoan fragments, including the oldest-known crustacean feeding apparatus, almost complete bradoriid valves preserved in three dimensions, new types of scalidophoran teeth and scalids, and a wide range of cuticular elements of uncertain affinity. Further, an abundance of large and/or asymmetrical acritarchs and filamentous microfossils was recovered, contributing to a rare but expanding record of benthic Proterozoic-like forms among Cambrian OWMs. The recovered diversity of acritarchs and filamentous microfossils totals 50 form taxa, of which 19 are described for the first time in the region. Quantitative and semi-quantitative analyses of acritarch disparity suggest a substantial proportion of these form taxa represent taphomorphs and/or arbitrary portions of abundance peaks. Placing form species in the context of their wider morphological variations allows the recorded diversity to be pared down to 30 morphotypes. On this basis, the presumed life history of Skiagia-plexus acritarchs is updated following quantitative analysis of openings, inner bodies, and clustering patterns in the recovered population. Three additional morphotypes are interpreted as bloom-forming and/or colonial species. Collectively, the results of this PhD project demonstrate that a fundamentally different picture of Cambrian diversity emerges when the full spectrum of OWM size ranges and disparity is considered. Applying these methods to the wider Cambrian record clearly shows potential to refine our understanding of macroevolution and palaeoecology as modern ecosystems were being established.

Murray-Darling Freshwater Research CentreMDFRC item.The properties of Daphnia carinata King as a grazer for use in biomanipulation trials were investigated. Mesocosm experiments suggested that in water from a lake where D. carinata was scarce, phytoplankton was nutrient-limited and the manipulated biomass of zooplankton had no effect on total chlorophyll a, whereas in water from a lake where D. carinata was dominant, nutrients were not limiting and total chlorophyll a was negatively correlated with the manipulated biomass of zooplankton. When offered lake phytoplankton in feeding trials, D. carinata consumed all items present, including colonies of cyanobacteria and long filaments of diatoms. In large outdoor tanks with natural plankton, the biovolume of prokaryotic ultraplankton (possible predecessors of cyanobacterial blooms) was consistently reduced in the presence of D. carinata. There was no evidence of an adverse effect of single-celled Microcystis aeruginosa containing the peptide toxin microcystin-LR on D. carinata grazing rates or survival. Different concentrations of microcystin-LR in solution covering the range of toxicities observed during M. aeruginosa blooms (5-500 nM) had no effect on D. carinata grazing. The suppression of phytoplankton biomass by D. carinata grazing is one of several possible mechanisms that might be considered for biomanipulation in Australia.

Knjiga se bavi znanstvenim aspektom Plitvičkih jezera kroz geologiju, hidrologiju, kemiju i najvećim dijelom biologijom.

Murray-Darling Freshwater Research CentreMDFRC item.Both phytoplankton and bacterioplankton produce alkaline phosphatases, but the techniques currently available for discriminating between the two sources are poor, especially when samples are from turbid waters. A novel approach, based on the differential inhibition of alkaline phosphatases by various physical and chemical treatments, was assessed as a rapid and inexpensive technique for determining whether phytoplankton or bacterioplankton were the more important producers of alkaline phosphatases in turbid rivers of south-eastern Australia. Eight phytoplankton strains and 14 bacterial strains (eight isolated from the Ovens River and six isolated as bacterial contaminants of the phytoplankton cultures) were grown in laboratory culture. Rates of alkaline phosphatase activity in the bacterial cultures varied from 70% of cases) grouped separately from those of the laboratory cultures of bacteria and phytoplankton, perhaps because the microbes studied in laboratory culture were not representative of native assemblages or because the culture conditions did not mimic those in nature. Nevertheless, differential-inhibition techniques have much potential for determining the origin of the alkaline phosphatases found in natural waters, with the major factor limiting their application being the collection of valid inhibition profiles for native bacterial and algal communities.

La Trobe University Faculty of Science, Technology and Engineering Murray Darling Freshwater Research CentreMDFRC item.1. River metabolism was measured over an annual cycle at three sites distributed along a 1000 km length of the lowland Murray River, Australia.2. Whole system metabolism was measured using water column changes in dissolved oxygen concentrations while planktonic and benthic metabolism were partitioned using light-dark bottles and benthic chambers.3. Annual gross primary production (GPP) ranged from 775 to 1126 g O2 m−2 year−1 which in comparison with rivers of similar physical characteristics is moderately productive.4. Community respiration (CR) ranged from 872 to 1284 g O2 m−2 year−1 so that annual net ecosystem production (NEP) was near zero, suggesting photosynthesis and respiration were balanced and that allochthonous organic carbon played a minor role in fuelling metabolism.5. Planktonic rates of gross photosynthesis and respiration were similar to those of the total channel, indicating that plankton were responsible for much of the observed metabolism.6. Respiration rates correlated with phytoplankton standing crop (estimated as the sum of GPP plus the chlorophyll concentration in carbon units), yielding a specific respiration rate of −1.1 g O2 g C−1 day−1. The respiration rate was equivalent to 19% of the maximum rate of phytoplankton photosynthesis, which is typical of diatoms.7. The daily GPP per unit phytoplankton biomass correlated with the mean irradiance of the water column giving a constant carbon specific photon fixation rate of 0.35 gO2 g Chl a−1 day−1 per μmole photons m−2 s−1 (ca. 0.08 per mole photons m−2 on a carbon basis) indicating that light availability determined daily primary production.8. Annual phytoplankton net production (NP) estimates at two sites indicated 25 and 36 g C m−2 year−1 were available to support riverine food webs, equivalent to 6% and 11% of annual GPP.9. Metabolised organic carbon was predominantly derived from phytoplankton and was fully utilised, suggesting that food-web production was restricted by the energy supply.