Bacteria and cyanobacteria can appear as single-cells or as colonial forms in aquatic systems along a wide spectrum of trophic conditions. Single cells aggregate or divide in an extracellular matrix forming a microcolony. The success of one variant over the other can depend on physical and/or biological factors. High irradiance can affect picocyanobacteria aggregation in the short-term, as well as grazing which induces morphological transformations of the cell surface thus facilitating microcolony formation. High substrate concentrations, as well as the presence of nutrient particles, can promote the aggregation of heterotrophic bacteria. The activity of grazers directly induces aggregation of bacteria (large aggregates escape predation) and indirectly favours aggregating strains by removing competitive non-aggregating bacteria. This session encourages contributions on the dynamics of bacterial and cyanobacterial microcolonies and aggregates in freshwater and marine environments along a trophic gradient to compare the role of colonial and single-cell morphotypes. Laboratory experiments to understand the role of aggregation on biodiversity and fitness of the community are also welcome.
Hypersaline habitats have been common throughout Earth history, and indications are that climate change is contributing to the expansion of these habitats worldwide. Investigations of these habitats suggest they contain diverse microbial communities, and are hotspots of biogeochemical cycling that may yield novel taxa, associations, and biogeochemistry. We welcome contributions from studies of both benthic and planktonic realms as well as from freshwater and marine environments.
Conveners: Claudia Dziallas, University of Copenhagen, email@example.com; Hans-Peter Grossart, Leibniz-Institute for Freshwater Ecology and Inland Fisheries, firstname.lastname@example.org; Kam W. Tang, Virginia Institute of Marine Sciences, email@example.com
During the history of life on our planet, acquisition of symbiont-encoded metabolic pathways has allowed organisms to exploit new ecological niches. A mechanistic understanding of the interactions between host and symbionts as well as the role of symbionts in functional diversification and speciation is, however, currently lacking. In addition, the importance of symbioses for niche occupation and matter cycling in aquatic systems is still under-appreciated. Aquatic organisms are densely colonized on their internal and external surfaces by a wide variety of microorganisms, such as bacteria, fungi, algae, and protozoans. With the exception of a few pathogens, knowledge about the ecology of these microbial symbionts is scarce, such as their life cycles, their establishment and maintenance in the hosts, their interactions with adjacent microbes, and evolution of the host-symbiont systems. Eukaryotic organisms present specific microhabitats with very different environmental conditions than the surrounding water, and they may therefore support the proliferation and activities of distinct microbial communities with important biogeochemical consequences. For instance, earlier research has suggested that the guts of zooplankton and fish may support anaerobic microbial processes that otherwise cannot occur in the oxygen-rich water columns. Furthermore, the alteration of the host´s niche can lead to different matter cycling rates and may change biodiversity of the respective ecosystem. We invite researchers to present and discuss all aspects of symbioses in aquatic ecosystems. The goal is to promote exchanges among experts from various fields in highlighting new findings on the molecular and functional ecology of microbial symbioses as well as new conceptual approaches for future studies of symbioses in all aquatic ecosystems. Presentations that link symbioses to water and disease managements or science education are also welcomed.
Conveners:Richard B. Rivkin, Memorial University of Newfoundland, Canada, firstname.lastname@example.org; Louis Legendre, Laboratoire d'Oceanographie de Villefranche, France, email@example.com; M. Robin Anderson, Fisheries and Oceans Canada, Canada, firstname.lastname@example.org
Over 25 years ago, it was proposed that the biological carbon pump (BCP) transfers particulate organic carbon (POC) from surface waters into the deep ocean. Recently, it was suggested that in a parallel process, the microbial carbon pump (MCP) lengthens the residence time of carbon in the ocean through the production of refractory dissolved organic carbon (DOC) by heterotrophic prokaryotes. Both pumps lead to the sequestration of atmospheric CO2 in the ocean. Ongoing studies on responses of marine microbial communities to drivers that are both natural (e.g. atmospheric and ocean circulation, mixing) and anthropogenic (e.g. acidification, eutrophication, increased temperature) contribute to better understanding of the functioning of the two pumps. Microbes influence both the BCP (e.g. effects on community respiration or solubilisation of POC) and the MCP (e.g. effects on production of refractory DOC). This session invites marine microbiologists, biogeochemists, environmental scientists and modellers to report on empirical, synthetic and/or model studies that contribute to our understanding of the responses of the microbial community to the above drivers, and the consequences for carbon sequestration through the microbial and biological carbon pumps.
The patchy, microscale distribution of aquatic microbial communities is determined in large part by the presence of conglomerations of organic and inorganic particles suspended in the water column, i.e., lake, river, or marine “snow”. For decades and with a variety of techniques, these conglomerations have been shown to be small-scale patches of higher biomass and productivity compared to surrounding water. These hotspots of microbial processes harbor pathogens, facilitate quorum sensing and genetic exchanges, and physically focus biogeochemical processes, even anoxic ones. This special session will update the “aggregate community” about the cornucopia of topics generated by recent studies of marine snow and its freshwater analogs.
The interstitial spaces inside sea ice constitute a vast habitat for both microorganism and animal life. Sea ice primary production exceeds that of the water column in early spring, therefore extending the duration of the productive season in ice-covered seas and providing an important resource for consumers. Melting sea ice releases immured sea ice organisms into the open water, seeding ice edge blooms and constituting a source of particulate as well as dissolved organic carbon. In a warming Arctic Ocean, the sea ice communities and associated carbon fluxes will likely be affected by later sea ice formation, earlier melt and varying snow cover. In this session we invite studies which report on the biology and biogeochemistry of sea ice biota and its role in the polar biogeochemistry and ecology, as well as its susceptibility to climate change.
Conveners: Lasse Riemann, University of Copenhagen, Denmark, email@example.com; Jonathan P. Zehr, University of California, USA, firstname.lastname@example.org; Julie LaRoche, Dalhousie University, Canada, email@example.com
Nitrogen cycling in marine waters is largely mediated by microbes. Bacteria or Archaea transform organic and inorganic nitrogen into bioavailable nutrients supporting productivity at local and global scales. Despite being essential for carbon biogeochemistry, many aspects of the marine nitrogen cycle remain poorly constrained and understood. Magnitudes of sources and sinks of nitrogen have been intensively debated throughout the last decade without reaching consensus. Recent discoveries of new organisms and pathways relevant for the oceanic nitrogen cycle along with developments of new applications of tracer techniques, molecular biology, and ‘omics’ have provided important new insights. In future endeavors to understand the marine nitrogen cycle it will be essential to examine the diversity and composition of microbial assemblages responsible for nitrogen transformations and, in particular, identify rates of activity for key microbes. In turn, this will promote the identification of environmental drivers important for the cycling of nitrogen, and facilitate establishment of couplings between key organisms, functional genes, and process rates. The session goal is to promote exchange among researchers from various fields to integrate data on biogeochemistry and process rates with the molecular ecology of microbes to facilitate understanding, modeling, and ultimately, prediction of nitrogen transformations in the sea.
Conveners: Miroslav Macek, National Autonomous University of Mexico, campus Iztac, firstname.lastname@example.org; Rosaluz Tavera, National Autonomous University of Mexico, Faculty of Science, email@example.com
Studies of spatial and annual development of autotrophic picoplankton (APP) in oligotrophic, stratified monomictic and meromictic lakes are scarce. Some studies (e.g., lakes Biwa, Kivu, Tanganyika) lacked comprehensive information on heterotrophic bacteria, protists and viruses. Even the more detailed studies (e.g., lakes Kinneret, Alchichica) also did not provide any clear explication for the high APP abundances compared to the total phytoplankton or their low rate of removal. Although APP accumulation in suboxic layers has been observed, its importance is not well understood. It has been hypothesized that water column stratification along with bottom-up control are dominant mechanisms regulating APP development, while APP removal is driven by mixotrophic flagellate- and ciliate-feeding combined with the use of sequestered APP photosynthate under an optimum light and suboxic condition. The aim of the session is to discuss up-to-date information on the annual pattern of APP and their contribution within the microbial-loop, and their relationships with limnological conditions (temperature, dissolved oxygen, photosynthetically-active radiation, nutrients) and protistan feeding. The importance of suboxic layers in these processes are of particular interest.
The future of coastal communities will depend on informed use of fresh and saltwater resources. Groundwater discharge is distinct from other coastal freshwater inputs due to its diffuse nature and in the quantity and composition of nutrients it delivers. Although the detection and quantification of coastal groundwater inputs has advanced considerably, understanding of its ecological role for microbial communities and coastal food webs has not. Groundwater-derived inputs of nutrients and organic matter are mediated by microbial communities in aquifers and sediments and play an important but under- recognized role in coastal water quality. The subsequent effect of groundwater inputs on the ecology of benthic and pelagic microbes such as phytoplankton is also poorly understood, even though it has been linked to phenomena such as harmful algal blooms (HABs). This session will address how within-aquifer microbial processes control the flux of groundwater-derived materials to coastal water bodies as well as the consequences of this flux for microbial and phytoplankton communities. Studies that integrate physical and chemical measurements of groundwater with biological processes are especially encouraged. Groundwater is often out of sight and out of mind, so studies that bring related issues into the public sphere or policy discussions are also encouraged.
Conveners: Jennifer J Mosher, Stroud Water Research Center, firstname.lastname@example.org; Richard Devereux, US Environmental Protection Agency, Devereux.Richard@epamail.epa.gov; Anthony V Palumbo, Oak Ridge National Lab, email@example.com
Aquatic ecosystems are globally connected by hydrological and biogeochemical cycles. Microorganisms inhabiting aquatic ecosystems form the basis of food webs, mediate essential element cycles, decompose natural organic matter, transform inorganic nutrients and metals, and degrade anthropogenic pollutants. The geochemical milieu determines the availability of resources that can be physiologically exploited by microorganisms. It is these interactions between the microorganisms and their resources that most likely contribute to metabolic diversity and determine whether one aquatic ecosystem is a source or sink for organic or inorganic materials with another. Understanding linkages among aquatic microorganisms, geochemical cycling, and hydrological transport is a vital step for managing anthropogenic inputs to aquatic environments and developing sustainable solutions for ecosystem protection. The goal of this session is to explore these linkages through presentations that include ecophysiological capacities of microbial communities in the transformation of matter through hydrologically connected ecosystems from streams and rivers to lakes or coastal zones and oceans. Research and policy focused contributions addressing these interactions in aquatic ecosystems are welcome.
Conveners: James Hollibaugh, University of Georgia, Dept. Marine Sciences, firstname.lastname@example.org; Jennifer Bowen, University of Massachusetts at Boston, Dept. Biology, email@example.com; Chris Francis, Stanford University, Dept. Environmental Earth System Science, firstname.lastname@example.org; Bradley Tolar, University of Georgia, Dept. Microbiology, email@example.com
Ammonia oxidation is a key process in the global biogeochemistry of nitrogen and a critical step in the conversion of fixed nitrogen to dinitrogen gas. Ammonia oxidation coupled to denitrification helps eliminate excess fixed nitrogen from coastal waters, alleviating eutrophication caused in part by excess loading of anthropogenic nitrogen. Both processes contribute to the flux of N2O, a potent greenhouse gas. This session will bring together scientists studying nitrogen dynamics, particularly ammonia oxidation and denitrification, focusing on populations of ammonia-oxidizing Bacteria and Archaea and denitrifiers in coastal waters and sediments, including estuaries, continental shelves, and coral reefs. Presenters are asked to address one or more of the following questions: What is the temporal variation in populations of ammonia oxidizers and denitrifiers? How does their activity, as a population and on a per cell basis, vary seasonally? What is their contribution to nitrogen dynamics, including production of nitrous oxide? What factors in their ecophysiology contribute to niche differentiation? What progress have we made on including more explicit formalizations of the process of ammonia oxidation and denitrification in models of nutrient cycling in coastal environments?
It is well established that atmospheric depositions of aerosols (such as black carbon) and dust are major local and global climate forcing factors. Also, recent research indicates that atmospheric deposition influences the diversity of microorganisms and microbe-mediated ecosystem functioning in the ocean. However, its influence on the (micro)biota is still poorly studied. This session brings together researchers from different scientific fields such as marine biology and biological oceanography, population and community ecology, diversity research and trophic ecology, and biogeochemistry. The aim is to summarize the research on the effect of atmospheric deposition on the microbiota, compare the effect of various factors such as black carbon and desert dust (and others), evaluate recent developments and potentially come up with a common position paper on global change, atmospheric deposition and the marine microbial life written by interested participants.
The remineralization rate of organic matter is determined by interactions between chemical structure and the metabolic capabilities of the heterotrophic community. The well- established size-reactivity continuum posits that particulate and high-molecular-weight dissolved organic matter is on average more reactive than smaller molecules, however the mechanisms driving the relationship between molecular size and reactivity remain poorly understood. Understanding the pathways by which specific macromolecules (e.g. specific polysaccharides or proteins) or randomly-structured polymers (e.g. lignin and humic substances) are remineralized is a particular challenge, since determining the structure of these macromolecules is often difficult. This session will combine research on the chemical structure and physical associations of organic macromolecules in aquatic environments with research on the biological mechanisms by which they are degraded.
Chemosynthesis is increasingly recognized to be more widespread and of larger significance in the ocean than previously thought. However, while a future ocean is expected to lead to an expansion of oxygen minimum zones supporting chemosynthetic processes, we currently lack a basic understanding of the main players, the pathways involved, and the regulation of energy and carbon transfer. This is even true for such charismatic environments as hydrothermal vents and cold seeps, where the general role and importance of chemosynthesis is well documented. Recent research further indicates that chemosynthesis plays a critical, yet currently poorly constrained role in other parts of the ocean system, most notably oxygen minimum zones and the deep-ocean subsurface. Recent advances in ‘omic’ technologies, functional assays of enrichments, and single-cell analysis make it now possible to obtain insights into the function of these microbial communities at an unprecedented level. Linking these ‘omic’ approaches to geochemical investigations and incorporating these data into innovative models presents great opportunities to advance our understanding of chemosynthetic communities and processes. Submissions from different lines of investigations using these approaches either in isolation or in combination are encouraged.
Interspecies interactions are at the core of success or failure of microbial species. For example, heterotrophic microbes are notoriously dependent on fixed carbon produced by autotrophic microalgae for survival. At the same time, many autotrophs acquire essential nutrients and metabolites from associated heterotrophic bacteria. Such interactions are an important feature of microbial communities, where synergism or competition among species contributes to ecosystem diversity and biogeochemical cycling. Next generation sequencing technologies and innovative experimental approaches are yielding unprecedented insights into these relationships and interactions and their influence on nutrient cycles. We invite contributions from laboratory and field studies that examine interactions between microbes in aquatic systems and their impact on local or global biogeochemistry. Research highlighting the biogeochemical importance of microbial associations, the role of interspecies communication in mediating interactions, or the role of climate change on microbial interactions is encouraged.
The web of interactions between photoautotrophs and other microbes is appearing to be increasingly complex. Predation, allelopathy, mutualism, cell-cell communication, cell-cell carbon transfer, vitamin interactions, etc are some examples of the spectrum of possibly important processes that go beyond the ‘bottom up’ look at ecology and evolution. This special symposium will examine the latest developments in this field. Examples of the communication of this research to broader audiences and K-12 education are welcome.
Two-decades of genomics-enabled exploration have revealed the ocean’s major microbial taxa and have begun to constrain their physiological potential. Simultaneously, analytical advances in biogeochemistry have opened new windows into the dynamics of metals and biomolecules in marine systems. While global sectional datasets of nutrients, radiotracers, and the carbon dioxide system continue to elucidate key oceanographic processes, sectional studies of genomes, metals, and biomolecules are also yielding important insights. Combining complementary ocean sections of geochemical, genomic, and biomolecular data has the potential to reveal new feedbacks between global environmental change and the biogeography of marine microbes (e.g. connections between shifts in microbial community structure, migrations of ocean biome boundaries, and alterations in marine ecosystem services). We invite the presentation of studies where sectional genomic or biomolecular datasets have been integrated with sectional geochemical datasets (e.g. GEOTRACES) to explore the biogeochemical functions of microbes in aquatic ecosystems (marine, estuarine, lacustrine). In addition to ocean-basin scale studies, we encourage submissions describing smaller scale studies that might serve as models for future global-scale efforts. Studies utilizing sectional genomic or biomolecular datasests to relate microbial biogeography to geochemical gradients are particularly welcome.
Conveners: Katherine McMahon, University of Wisconsin Madison, USA, firstname.lastname@example.org; Stefan Bertilsson, Uppsala University, Sweden, email@example.com; Hans-Peter Grossart, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, IGB-Berlin, firstname.lastname@example.org
Freshwater microbial communities are highly dynamic, with drivers of change operating at multiple time scales ranging from minutes to years. Regular and consistent sampling of communities and rich contextual environmental data across these time scales is necessary in order to develop a deep and predictive understanding of how communities assemble and perform key ecosystem functions. This session will feature research that embraces the use of time series and high-resolution spatial sampling to study freshwater microbial communities with a variety of techniques including next- generation sequencing-enabled tag sequencing, metagenomics, fluorescent in situ hybridization, automated samplers, and high-frequency in situ sensor monitoring. The potential for near-real-time monitoring of harmful cyanobacterial blooms to enable now-casting water quality models and early warning systems for public health authorities will be emphasized. A recent new joint initiative launched by the Earth Microbiome Project (http://www.earthmicrobiome.org/) and the Global Lakes Ecological Observatory Network (GLEON) (http://www.gleon.org/) will be highlighted.