Sophie C. Leterme

Distribution of picophytoplankton communities from brackish to hypersaline waters in a South Australian coastal lagoon

BackgroundPicophytoplankton (i.e. cyanobacteria and pico-eukaryotes) are abundant and ecologically critical components of the autotrophic communities in the pelagic realm. These micro-organisms colonized a variety of extreme environments including high salinity waters. However, the distribution of these organisms along strong salinity gradient has barely been investigated. The abundance and community structure of cyanobacteria and pico-eukaryotes were investigated along a natural continuous salinity gradient (1.8% to 15.5%) using flow cytometry.ResultsHighest picophytoplankton abundances were recorded under salinity conditions ranging between 8.0% and 11.0% (1.3 × 106 to 1.4 × 106 cells ml-1). Two populations of picocyanobacteria (likely Synechococcus and Prochlorococcus) and 5 distinct populations of pico-eukaryotes were identified along the salinity gradient. The picophytoplankton cytometric-richness decreased with salinity and the most cytometrically diversified community (4 to 7 populations) was observed in the brackish-marine part of the lagoon (i.e. salinity below 3.5%). One population of pico-eukaryote dominated the community throughout the salinity gradient and was responsible for the bloom observed between 8.0% and 11.0%. Finally only this halotolerant population and Prochlorococcus-like picocyanobacteria were identified in hypersaline waters (i.e. above 14.0%). Salinity was identified as the main factor structuring the distribution of picophytoplankton along the lagoon. However, nutritive conditions, viral lysis and microzooplankton grazing are also suggested as potentially important players in controlling the abundance and diversity of picophytoplankton along the lagoon.ConclusionsThe complex patterns described here represent the first observation of picophytoplankton dynamics along a continuous gradient where salinity increases from 1.8% to 15.5%. This result provides new insight into the distribution of pico-autotrophic organisms along strong salinity gradients and allows for a better understanding of the overall pelagic functioning in saline systems which is critical for the management of these precious and climatically-stress ecosystems.

Substrate Type Determines Metagenomic Profiles from Diverse Chemical Habitats

Environmental parameters drive phenotypic and genotypic frequency variations in microbial communities and thus control the extent and structure of microbial diversity. We tested the extent to which microbial community composition changes are controlled by shifting physiochemical properties within a hypersaline lagoon. We sequenced four sediment metagenomes from the Coorong, South Australia from samples which varied in salinity by 99 Practical Salinity Units (PSU), an order of magnitude in ammonia concentration and two orders of magnitude in microbial abundance. Despite the marked divergence in environmental parameters observed between samples, hierarchical clustering of taxonomic and metabolic profiles of these metagenomes showed striking similarity between the samples (>89%). Comparison of these profiles to those derived from a wide variety of publically available datasets demonstrated that the Coorong sediment metagenomes were similar to other sediment, soil, biofilm and microbial mat samples regardless of salinity (>85% similarity). Overall, clustering of solid substrate and water metagenomes into discrete similarity groups based on functional potential indicated that the dichotomy between water and solid matrices is a fundamental determinant of community microbial metabolism that is not masked by salinity, nutrient concentration or microbial abundance.

MORPHOLOGICAL FLEXIBILITY OF COCCONEIS PLACENTULA (BACILLARIOPHYCEAE) NANOSTRUCTURE TO CHANGING SALINITY LEVELS1

Diatoms possess a silica frustule decorated with unique patterns of nanosize features. Here, we show for the first time from in situ samples that the size of the nanopores present at the surface of the diatom Cocconeis placentula Ehrenb. varies with fluctuating salinity levels. The observed reduction in nanopore size with decreasing salinity agrees with previous laboratory experiments. We also uniquely combined our observations with theoretical considerations to demonstrate that the decrease in the diffusive layer thickness is compensated for by the changes in pore size, which maintain a steady diffusive flux toward the diatom’s cell at different salinities. This process allows diatoms to absorb similar amount of nutrients whatever the salinity and as such to increase their ecological competitiveness in fluctuating environments. These results further suggest that the overall ecological success of diatoms, and their ability to react to environmental changes, may be controlled by the flexibility of the morphological characteristics of their frustules.

Diatom adaptability to environmental change: a case study of two Cocconeis species from high-salinity areas

This paper investigates the impact of natural change in salinity on the morphological plasticity of diatom frustules. In particular, this study uses as an example the highly saline lagoons of the Coorong wetlands in South Australia. These wetlands have been strongly impacted by the drought in South Australia (2004–2010) which has resulted in a salinity gradient of 40 to 134 psu along the wetlands. In this framework, the impact of some environmental variables (i.e., dissolved oxygen, pH, turbidity, salinity, temperature and nutrients) was investigated on the nanoscale features characterizing the cell wall of two diatom species, Cocconeis placentula Ehrenberg and C. pinnata Gregory. The results suggest that not only salinity, but also nutrient concentration play a significant role in the morphological plasticity of the frustule of these two diatom species. It is proposed that the morphological plasticity of the diatom frustules is species-specific and related to their immediate surrounding environmental conditions.

Increased Zooplankton Behavioral Stress in Response to Short-Term Exposure to Hydrocarbon Contamination

The swimming behavior of the calanoid copepod Centropages hamatus is used as a very sensitive real-time screening tool to assess hydrocarbon contamination in marine waters. A behavioral stress index based on the complexity of swimming sequences is suggested as a potential tool to critically assess behavioral responses to natural and anthropogenic forcing in the marine environment.

Over 75 years of zooplankton data from Australia

Zooplankton are the key trophic link between primary producers and fish in pelagic ecosystems. Historically, there are few zooplankton time series in Australia, with no data sets longer than two years prior to 2008. Here we compile 98 676 abundance records of more than 1000 zooplankton taxa from unpublished research cruises, student projects, published literature, and the recent Integrated Marine Observing System (IMOS). This data set covers the entire coastal and shelf region of Australia and dates back to 1938. Most records are for copepods, but there are also data for other taxa such as decapods, chaetognaths, thaliaceans, appendicularians, and cladocerans. Metadata are provided for each record, including dates, coordinates, and information on mesh size and sampling methods. To facilitate analysis across the multiple data sets, we have updated the species names according to the World Register of Marine Species (WoRMS) and converted units to abundance per cubic meter. These data will be valuable for studies of biodiversity, biogeography, impacts of climate change, and ecosystem health. We encourage researchers holding additional Australian zooplankton data to contact us and contribute their data to the data set so we can periodically publish updates.

Approaches for the detection of harmful algal blooms using oligonucleotide interactions

AbstractBlooms of microscopic algae in our waterways are becoming an increasingly important environmental concern. Many are sources of harmful biotoxins that can lead to death in humans, marine life and birds. Additionally, their biomass can cause damage to ecosystems such as oxygen depletion, displacement of species and habitat alteration. Globally, the number and frequency of harmful algal blooms has increased over the last few decades, and monitoring and detection strategies have become essential for managing these events. This review discusses developments in the use of oligonucleotide-based ‘molecular probes’ for the selective monitoring of algal cell numbers. Specifically, hybridisation techniques will be a focus. Graphical Abstractᅟ

Anthropogenic shift of planktonic food web structure in a coastal lagoon by freshwater flow regulation

Anthropogenic modification of aquatic systems has diverse impacts on food web interactions and ecosystem states. To reverse the adverse effects of modified freshwater flow, adequate management of discharge is required, especially due to higher water requirements and abstractions for human use. Here, we look at the effects of anthropogenically controlled freshwater flow regimes on the planktonic food web of a Ramsar listed coastal lagoon that is under recovery from degradation. Our results show shifts in water quality and plankton community interactions associated to changes in water flow. These shifts in food web interactions represent modifications in habitat complexity and water quality. At high flow, phytoplankton-zooplankton interactions dominate the food web. Conversely, at low flow, bacteria, viruses and nano/picoplankton interactions are more dominant, with a substantial switch of the food web towards heterotrophy. This switch can be associated with excess organic matter loading, decomposition of dead organisms, and synergistic and antagonistic interactions. We suggest that a lower variability in flow amplitude could be beneficial for the long-term sustaining of water quality and food web interactions, while improving the ecosystem health of systems facing similar stresses as the Coorong.

A database of marine phytoplankton abundance, biomass and species composition in Australian waters

There have been many individual phytoplankton datasets collected across Australia since the mid 1900s, but most are unavailable to the research community. We have searched archives, contacted researchers, and scanned the primary and grey literature to collate 3,621,847 records of marine phytoplankton species from Australian waters from 1844 to the present. Many of these are small datasets collected for local questions, but combined they provide over 170 years of data on phytoplankton communities in Australian waters. Units and taxonomy have been standardised, obviously erroneous data removed, and all metadata included. We have lodged this dataset with the Australian Ocean Data Network (http://portal.aodn.org.au/) allowing public access. The Australian Phytoplankton Database will be invaluable for global change studies, as it allows analysis of ecological indicators of climate change and eutrophication (e.g., changes in distribution; diatom:dinoflagellate ratios). In addition, the standardised conversion of abundance records to biomass provides modellers with quantifiable data to initialise and validate ecosystem models of lower marine trophic levels.

Evaluation of transparent exopolymer particles and microbial communities found post-UV light, multimedia and cartridge filtration pre-treatment in a SWRO plant

AbstractSeawater reverse osmosis desalination is affected greatly by membrane biofouling which reduces membrane lifetimes and increases cost of permeate production. This work reports on the analysis of pre-treated seawater from a small-scale desalination plant operating with a three-stage pre-treatment system namely, (1) medium-pressure ultraviolet (MP-UV) disinfection, (2) multimedia filtration (MMF), and then finally, (3) cartridge filtration. Transparent exopolymeric particles (TEPs), chlorophyll a, phytoplankton, bacteria and viruses were evaluated in the pre-treated seawater after each pre-treatment stage over a one-year period (July 2012–July 2013). The concentration of TEPs was found to occasionally increase after MP-UV disinfection. MP-UV disinfection had no effect on the phytoplankton, bacterial or viral cell counts. In contrast, MMF was shown to be the most efficient step in removing TEPs and micro-organisms from seawater, while this removal was less significant for viruses. Cartridge filters ha...