Curriculum Vitae
Dr. Bas W. Ibelings (1962) graduated from Nijmegen University in 1987. He continued to do a PhD. at the University of Amsterdam on the role of buoyancy on the population dynamics of bloom forming cyanobacteria (completed 1992). Next he worked for 3 years at the University of Bristol (U.K.) and Centre for Ecology and Hydrology in Windermere on microgradients and physiological activity in dense surface scums of cyanobacteria. In 1995 and 1996 he worked as an ecological consultant for HASKONING in Nijmegen. Subsequently he moved to the Ecology Department of RIZA, first as a phytoplankton specialist, from 1998 onwards also as Program Manger Lake Ecology. In 2001 he started working on a tenure track position at NIOO-KNAW (Department of Aquatic Ecology) on a project investigating host-parasite interactions in freshwater phytoplankton. His research is centred on biodiversity in a wide sense, ranging from the evolutionary origin of biodiversity to the role of biodiversity in determining ecosystem services. Approaches vary from experimental evolution using phototrophic microorganisms, to competition experiments in chemostats, foodweb studies in mesocosms and automated, high frequency monitoring of functional plankton traits in lakes. The role of ecological and evolutionary processes in shaping plankton community assembly is studied in the deep, alpine Lake Zurich and the shallow lake IJsselmeer. Next to the more fundamental lines of work the applied research on harmful cyanobacteria is continued, with a focus on foodweb effects of cyanotoxins. Both in fundamental and strategic research genomic tools like microarrays are used to deepen our understanding of the genetic basis of ecological responses. From 2007 onwards Bas Ibelings worked as a group leader in the Swiss Federal Institute of Aquatic Sciences and Technology (Eawag). Currently he holds a position as senior scientist at NIOO-KNAW (Department of Aquatic Ecology), whilst he retains a position at Eawag as an adjunct scientist.
Summary CV:
- Present Senior Scientist -NIOO, Netherlands
- 2007-2009 Group Leader - Eawag, Switzerland
- 2001-2007 Tenure track - NIOO, Netherlands
- 1998–2001 Program Leader Lake Ecology - RIZA, Netherlands
- 1997-2001 Project-leader Plankton Research – RIZA
- 1995-1996 Consulting ecologist - Royal HASKONING, Netherlands
- 1992-1995 Post doctoral Research Fellow - University of Bristol, England
- 1987-1992 PhD - University of Amsterdam
Expertise
- Plankton community assembly
- Ecology and physiology of bloom forming cyanobacteria
- Ecological effects of cyanobacterial toxins
- Co-evolution of host and parasites and resource competitors
- Experimental evolution (serial passage experiments)
- Chytrids (primitive fungi of phytoplankton)
- Microarrays (gene expression studies)
Knowledge transfer
About once a year I write a contribution to Kennislink.nl, a website aimed at transfer of scientific knowledge at the secondary school level. Below are two links to articles I have written: one on the rsisk of recreation in lakes supporting dense populations of toxic blue-green algae and one on algae carrying parasitic fungi (both in Ducth).
http://www.kennislink.nl/web/show?id=96781&vensterid=811&cat=60360
http://www.kennislink.nl/web/show?id=116707&vensterid=811&cat=60360
Projects
Co-evolution of resource competitors
In this experiment the cyanobacterium Synechocystis and the unicellular green alga Chlamydomonas are grown together as resource competitors (nitrogen) for hundreds of generations. Using serial passage we allow evolution of the two phototrophs under stressful conditions. Snaphsots from the evolution are stored in a so-called frozen fossil bed. Improvements in fitness are tested in direct head to head competition between ancestor and evolved strain. Adaptations to N-limitation are also tested by growing ancestral and evolved strains - harvested from the serial passage experiment - in chemostats. In the chemostat cells are exposed to transient conditions in the availability of N (see pictures). Both changes in physiology and in genome wide gene expression are examined during the transient state. Genes that change their expression over evolutionary time scales are candidate genes for mutations underlying the adaptive evolution; these will be sequenced. What we hope to find is experimental support for the notion of character displacement, resulting in a reduction in the strength of the competition with time, which would be to the benefit of both competitors.
 
Synechocytis (ancestral strain) during transient state experiment in chemostats. Transient conditions in the availability of N are clearly visible in pigmentation of the cells
Adaptive radiation and niche construction in Pseudomonas
Experiments by Paul Rainey and co-workers have demonstrated remarkable diversification of when static micromicrocosms are inoculated with a single clone of Pseudomonas fluorescens. Mutants arise that quickly colonize different niches in the microcosm, one colonizes the interface between broth and air, another the bottom of the microcosms etc. This process of adaptive radiation is prohibited when the microcosms are shaken. In their papers (e.g. Nature 394: 69-71) Rainey et al put forward that especially spatial heterogeneity in the availability of oxygen drives resource competition and through this adaptive radiation. In a collaboration between NIOO, MPI Marine Microbiology and Massey University we set out to map the complex environment which is required for diversification of the bacterial community (heterogeneity in the availability in oxygen), which is the outcome of the activity of the bacteria themselves. In the study we manipulate the availability of oxygen (slope of the resource gradient) in diffusion chambers, we analyze (micro)gradients in the physical environment using microelectrodes and we asses the resulting microbial diversity on plates. See pictures:
  
Vials containing Pseudomoans fluorescens, close up of micro-electrodes touching surface of Pseudomonas mats, and rotating cylinders containing Pseudomonas vials under different oxgen atmospheres
Fungal parasites in the phytoplankton
Chytrids are primitive fungi that parasitize on a wide group of organisms, including phytoplankton. In our study we are interested in the potential for co-evolution to shape the interactions between the chytrid Zygorhizidium planktonicum and its (diatom) host Asterionella formosa. Bi-yearly epidemics of this chytrid are observed in several Dutch lakes (but see below). The prevalence of infection commonly exceeds 90 % and every infection kills the host cell, so that the impact of parasitism on the host population is severe. Genetic analysis of the population structure of Asterionella in a number of lakes indicated that the high level of genetic diversity could only be explained by recombination through sexual reproduction. Genetic host diversity may play a role in fending off parasites, and indeed in a serial passage experiment it was shown that host genetic diversity held back parasite evolution. Nevertheless these fungal parasites are very effective in infecting their hosts in the field. Further experiments with isolated clones from host and parasite indicated local adaptation, in which parasites were more successful on their own local hosts, than on foreign hosts from other locations. Survival - even blooming of the host - under these severe fitness costs, with recurring epidemics of a highly virulent parasite, seem greatly dependent on refuges for the host, especially on the sediment where the parasite is not infective. Currently we focus more on parasite driven microevolution of Asterionella in the field, and on the interaction between disease and environmental stress factors like pollutants and climate change. Climate change (mild winters without ice-cover) seem to have a large impact on interactions between Asterionella and the chytrid. The disease rarely reaches epidemic levels anymore, except in those rare cases where winters are severe, with extended ice-cover. Periods in which water temperature drops below 3 oC render the parasite unifective, giving the host a disease-free window of opportunity to build up a bloom. Climate warming in a paradoxical way has reduced the impact of the parasite, and is yet detrimental to both host and parasite. On-going theoretical and empirical research tries to unravel the causes for this impact of climate change.
 
Light and EM photographs of chytrid parasites on Asterionella host cells
Cyanobacterial toxins in lake foodwebs
Cyanobacteria produce a wide range of bioactive compounds, including some well known toxins like microcystin. It has been suggested that these microcystins play a role in mass mortalities of fish and waterfowl. We study the presence (concentrations) and effects of cyanobacterial toxins in a range of aquatic biota, including zooplankton, zebra mussels and fish. Microcystins were found throughout the foodweb, including species that do not feed directly on phytoplankton, indicating that vectorial transport of these toxins takes place. Nevertheless no indications for biomagnification were found, which would otherwise have exposed higher trophic levels to much higher concentrations. Zebra mussels accumulate very little of the toxin, and appear largely unaffected. Zooplankton, including Daphnia spp. accumulated much more of the toxin, and life history experiments showed that they were much more sensitive, although this was partly dependent on the presence of alternative food. Fish exposed to microcystin through their food developed severe liver damage (like that seen in lakes supporting blooms of cyanobacteria), but did not die from exposure to the toxin. Fish kills seem to be the result of a multitude of stress factors that co-occur during blooms of cyanobacteria. Current work is focusing on interactions between cyanobacterial toxins and other filter feeder stress factors, like poor food quality (C:P ratio of the seston), and climate change.
 
Floating surface blooms of toxic cyanobacteria
Lake plankton community assembly
Standard plankton monitoring misses most of the relevant temporal and spatial dynamics. In a rapidly changing world, innovative approaches to ecosystem monitoring and its integration with ecosystem models are required. Ideally what would be needed is an automated, stand alone system for sampling, cell counting and classification of phytoplankton. Recent developments in scanning flowcytometry may offer these requirements in a single instrument, called Cytobuoy. CytoBuoy data may allow the detection of detailed patterns in plankton community dynamics as a first step towards understanding biodiversity and its drivers; it provides a context for further experimental study of causal mechanisms. Cytobuoy data are organized as presence-absence matrices and studied for presence of assembly rules using different metrics. Assembly rules formalize the quest for patterns in diversity and abundance of species and restrict the realm of ‘permissible’ species combinations that are likely to assemble from regional species pool. Two main opposing forces act in plankton community assembly. Habitat filtering results in the co-occurrence of closely related species more often than predicted by chance (phylogenetic clustering), whereas resource competition results in the opposite pattern, i.e. overdispersion of closely related species. The final community composition will reflect the relative importance of these two rival processes. In addition the nature of the traits involved in community assembly (conserved vs. convergent evolution) affect the patterns observed. In the analysis we combine traditional taxonomic data on phytoplankton diversity with information on functional trait diversity. Functional diversity has a more direct relationship with ecosystem-functioning and services. High frequency, automated monitoring of the functional community structure has been set up for the deep Alpine Lake Zurich and the shallow lake IJsselmeer.
 
Platform for automated monitoring of phytoplankton (Lake Lucerne) and principle of phytoplankton-traits monitoring using CytoBuoy flowcytometry
Co-Operation
Prof. dr. Jef Huisman - Aquatic Microbiology - University of Amsterdam
Resource competition of phytoplankton species, chaotic behaviour of natural plankton communities
Prof. dr. Hans C.P. Matthijs - Aquatic Microbiology - University of Amsterdam
Microarrays of Synechocystis and Microcystis
Prof. dr. Marten Scheffer - Aquatic Ecology - Wageningen University and Research Centre
Regime shifts in lakes
Prof. dr. Paul B. Rainey – New Zealand Institute for Advanced Study
Experimental evolution of Pseudomonas
Prof Dr Jukka Jokela & dr Piet Spaak, Eawag, Department of Aquatic Ecology
Host parasite interactions
Dr Francesco Pomati & dr Blake Matthews, Eawag
Community assembly of phytoplankton
GLEON members (http://gleon.org/)
Automated high frequency lake monitoring
Deltares
Selected Publications
Below are a just three representative publications. For a complete list of publications - see under downloads
Chytrid infections of diatom spring blooms: paradoxical effects of climate warming on fungal epidemics in lakes
Bas W. Ibelings, Alena S. Gsell, Wolf M. Mooij, Ellen van Donk, Silke van den Wyngaert and Lisette N. de Senerpont Domis
Freshwater Biology 56, 754-766 (2011)
Full article: http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2427.2010.02565.x/pdf
Abstract. Spanning a period of more than 30 years dynamics in host parasite interactions between the freshwater diatom Asterionella formosa and two different, but in their pathogenic effects similar chytrid parasites, Rhizophydium planktonicum and Zygorhizidium planktonicum were studied in Lake Maarsseveen, The Netherlands. Water temperature over the period of study shows a significant warming trend, strongest of all in spring. The key spring event in lakes is the diatom spring bloom, in many years dominated by Asterionella, which acts as a host for highly abundant and virulent chytrid parasites. We study if and how climate warming has affected the occurrence and severity of disease. In years with cold winters / early springs the host first builds up a dense bloom, which only later is followed by epidemic development of the fungal disease; high Asterionella densities greatly facilitate transmission of the parasites by chytrid zoospores. This sequence of events is absent in milder winters. Based upon earlier experimental studies we know that at water temperatures below 3oC Asterionella rapidly outgrows the parasite, and the parasite is almost non-infective offering a disease free window of opportunity for growth of Asterionella. Overall the picture that emerges from the lake data is one in which climate warming has reduced periods in which water temperature remains < 3 oC, narrowing the window of opportunity for uninfected growth. Consequently Asterionella continuously suffers from infection, albeit at low levels. The resulting species specific population losses weaken the position of Asterionella in the spring phytoplankton community, so that other diatoms – possibly through priority effects – take over as dominant species. The result is a much decreased Asterionella bloom and dominance shifting to other diatom species.Decreased Asterionella development has clear ramifications for disease, which in mild winters no longer reaches epidemic levels of infection, but remains at low prevalence since transmission is impaired at low host densities. Climate warming in intricate ways is affecting both host and parasite, whereby the host is denied a bloom and consequently the parasite is denied an epidemic. In contrast with findings in other lakes where timing of the spring Asterionella bloom has advanced, we observe that Asterionella blooms occur later in the season when winters are mild; we link this phenology shift to severe infections in colder years. A shift from Asterionella to a mixed diatom community in years with mild winters should benefit the foodweb, because of the poor edibility of Asterionella, unless the numerous chytrid zoospores produced during epidemics take over as main food source for the zooplankton. Our study underlines the complexity of environmental effects like climate warming on disease. A reduction in the likelihood of epidemic development of a virulent parasite would seem to be of great benefit to the host, but in a complex way this is not the case. It may serve as a warning against preliminary conclusions about a ‘warmer hence sicker world’. Unexpected, sometimes paradoxical consequences of climate change can and will occur.
Cell physiology of the cyanobacterium Synechocystis sp. Strain PCC6803 during transitions between nitrogen and light limited growth
Eneas Aquirre von Wobeser1, Bas W Ibelings1, Jasper Bok, Vladimir Krasikov, Jef Huisman de Senerpont Domis; 1these authors contributed equally to the work
Plant Physiology 155, 1445-1457 (2011)
Full article: http://www.plantphysiol.org/content/155/3/1445.abstract?sid=dc3d45f6-1910-4a6d-8066-bc32c36b54ce
Abstract. Physiological adaptation and genome-wide expression profiles of the cyanobacterium Synechocystis sp. strain PCC 6803 in response to gradual transitions between nitrogen-limited and light-limited growth conditions were measured in continuous cultures. Transitions induced changes in pigment composition, light absorption coefficient, photosynthetic electron transport, and specific growth rate. Physiological changes were accompanied by reproducible changes in the expression of several hundred open reading frames, genes with functions in photosynthesis and respiration, carbon and nitrogen assimilation, protein synthesis, phosphorus metabolism, and overall regulation of cell function and proliferation. Cluster analysis of the nearly 1,600 regulated open reading frames identified eight clusters, each showing a different temporal response during the transitions. Two large clusters mirrored each other. One cluster included genes involved in photosynthesis, which were up-regulated during light-limited growth but down-regulated during nitrogen-limited growth. Conversely, genes in the other cluster were down-regulated during light-limited growth but up-regulated during nitrogen-limited growth; this cluster included several genes involved in nitrogen uptake and assimilation. These results demonstrate complementary regulation of gene expression for two major metabolic activities of cyanobacteria. Comparison with batch-culture experiments revealed interesting differences in gene expression between batch and continuous culture and illustrates that continuous-culture experiments can pick up subtle changes in cell physiology and gene expression.
Resilience of alternative stable states during the recovery of shallow lakes from eutrophication: Lake Veluwe as a case study
Bas W Ibelings, Rob Portielje, Eddy HRR Lammens, Ruurd Noordhuis, Marcel S van den Berg, Willemien Joosse & Marie Louise Meijer
Ecosystems 10, 4-16 (2007)
Full article: http://www.springerlink.com/content/l2087h268173868t/
Abstract. In this paper we analyze a long-term dataset on the recovery from eutrophication of Lake Veluwe (The Netherlands). Clear hysteresis was observed in a number of ecosystem variables: the route to recovery differed significantly from the route that led to loss of clear water. The macrophyte dominated state disappeared in the late 1960s at TP above 0.20 mg l)1, whereas its return occurred at less than 0.10 mg TP / L. Several regime shifts resulting in the occurrence of three alternative stable states were observed over a period of 30 years. The turbid state showed resistance to change, despite a strong and prompt reduction in Chl-a following reduction of external P-loading. The most important component that determined hysteresis in the return to clear water was not internal P-loading, but a high level of nonalgal light attenuation (through sediment resuspension) maintained by the interaction between wind and benthivorous fish. Although Chara was able to re-colonize the most shallow parts of the lake, recovery stalled and for a number of years clear (above charophyte beds) and turbid (deeper parts of the lake) water co-existed, as a separate alternative state on route to full recovery. Lake-wide clear water was re-established after bream density had been reduced substantially. This allowed a return of zebra mussels to the lake, whose high filtration capacity helped in maintaining clear water. In this study, we were able to identify the main drivers of hysteresis and regime shifts, although formal demonstration of cause and effect was not possible on the basis of field data alone. We argue that resilience of the present clear water state of Lake Veluwe very much depends on sizable populations of a few keystone species, especially Chara (stoneworts) and Dreissena (zebra mussels), and that careful management of these species is equally important as control of nutrients. Lake management should strive to maintain and strengthen resilience of the ecosystem, and this should offer protection against a renewed collapse of the clear state.
A reprint or PDF can be requested at library@nioo.knaw.nl
Links
Why cutting budgets for science and education is not a clever idea:
https://www.nrc.nl/digitaleeditie/NH/2011/0/20110118___/1_09/article4.html
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