Cryospheric ecosystems: A synthesis of snowpack and glacial research

The fourteen letters that contributed to this focus issue on cryospheric ecosytems provide an excellent basis for considering the state of the science following a marked increase in research attention since the new millennium. Research letters from the focus issue provide significant insights into the biogeochemical and biological processes associated with snow, glacier ice and glacial sediments. This has been achieved via a significant, empirical effort that has given particular emphasis to glacier surface habitats. However, far less is known about aerobiology, glacial snow covers, supraglacial lakes and sub-ice sedimentary habitats, whose access for sampling and in-situ monitoring remains a great challenge to scientists. Furthermore, the use of models to explore key fluxes, processes and impacts of a changing glacial cryosphere are conspicuous by their absence. As a result, a range of process investigations and modelling studies are required to address the increasing urgency and uncertainty that is associated with understanding the response of cryospheric ecosystems to global change

Ace Lake: three decades of research on a meromictic, Antarctic lake

Ace Lake (Vestfold Hills, Antarctica) has been investigated since the 1970s. Its close proximity to Davis Station has allowed year-long, as well as summer only, investigations. Ace Lake is a saline meromictic (permanently stratified) lake with strong physical and chemical gradients. The lake is one of the most studied lakes in continental Antarctica. Here we review the current knowledge of the history, the physical and chemical environment, community structure and functional dynamics of the mixolimnion, littoral benthic algal mats, the lower anoxic monimolimnion and the sediment within the monimolimnion. In common with other continental meromictic Antarctic lakes, Ace Lake possesses a truncated food web dominated by prokaryote and eukaryote microorganisms in the upper aerobic mixolimnion, and an anaerobic prokaryote community in the monimolimnion, where methanogenic Archaea, sulphate-reducing and sulphur-oxidizing bacteria occur. These communities are functional in winter at subzero temperatures, when mixotrophy plays an important role in survival in dominant photosynthetic eukaryotic microorganisms in the mixolimnion. The productivity of Ace Lake is comparable to other saline lakes in the Vestfold Hills, but higher than that seen in the more southerly McMurdo Dry Valley lakes. Finally we identify gaps in the current knowledge and avenues that demand further investigation, including comparisons with analogous lakes in the North Polar region

Sex‐skewed trophic impacts in ephemeral wetlands

Predation can have marked impacts on ecosystem structure, function, and stability. However, quantifications of biotic interactions frequently overlook demographic variabilities within populations, which can modulate interaction strengths, such as sex and reproductive status. Compositional population ratios between males and females, alongside reproductive status, are highly variable temporally in ephemeral aquatic systems, and may profoundly mediate levels of ecological impact and thus stability of trophic groups. In the present study, we apply functional responses (resource intake as a function of resource density) to quantify predatory impacts of adult males, non‐gravid females, and gravid females of the calanoid copepod Lovenula raynerae (Diaptomidae), an abundant ephemeral pond specialist, on larvae of the Culex pipiens (Culicidae) mosquito complex. We then develop a novel metric to forecast population‐level impacts across different population sex ratio scenarios. Lovenula raynerae demonstrated prey population destabilising Type II functional responses irrespective of sex and reproductive status, yet variable functional response magnitudes were found. While male and non‐gravid female copepods exhibited similar functional response maximum feeding rates, gravid female feeding rates were substantially higher, implying higher resource demands for progeny development. Ecological impacts of L. raynerae on lower trophic groups increased markedly where their abundances increased but, crucially, also as population sex ratios became more biased towards gravid female copepods. We demonstrate that population‐level impacts do not only correlate tightly with abundance but may be further modulated by reproductive status variations. Thus, the development of sex‐skewed ratios in favour of gravid females during the hydroperiod probably heightens ecological impacts on lower trophic groups. The implications of these results for prey population stability are discussed in the context of freshwater ecosystems

Metagenomic Analysis of Lysogeny in Tampa Bay: Implications for Prophage Gene Expression

Phage integrase genes often play a role in the establishment of lysogeny in temperate phage by catalyzing the integration of the phage into one of the host's replicons. To investigate temperate phage gene expression, an induced viral metagenome from Tampa Bay was sequenced by 454/Pyrosequencing. The sequencing yielded 294,068 reads with 6.6% identifiable. One hundred-three sequences had significant similarity to integrases by BLASTX analysis (e≤0.001). Four sequences with strongest amino-acid level similarity to integrases were selected and real-time PCR primers and probes were designed. Initial testing with microbial fraction DNA from Tampa Bay revealed 1.9×107, and 1300 gene copies of Vibrio-like integrase and Oceanicola-like integrase L−1 respectively. The other two integrases were not detected. The integrase assay was then tested on microbial fraction RNA extracted from 200 ml of Tampa Bay water sampled biweekly over a 12 month time series. Vibrio-like integrase gene expression was detected in three samples, with estimated copy numbers of 2.4-1280 L−1. Clostridium-like integrase gene expression was detected in 6 samples, with estimated copy numbers of 37 to 265 L−1. In all cases, detection of integrase gene expression corresponded to the occurrence of lysogeny as detected by prophage induction. Investigation of the environmental distribution of the two expressed integrases in the Global Ocean Survey Database found the Vibrio-like integrase was present in genome equivalents of 3.14% of microbial libraries and all four viral metagenomes. There were two similar genes in the library from British Columbia and one similar gene was detected in both the Gulf of Mexico and Sargasso Sea libraries. In contrast, in the Arctic library eleven similar genes were observed. The Clostridium-like integrase was less prevalent, being found in 0.58% of the microbial and none of the viral libraries. These results underscore the value of metagenomic data in discovering signature genes that play important roles in the environment through their expression, as demonstrated by integrases in lysogeny

Biogeochemical Stoichiometry of Antarctic Dry Valley Ecosystems

Among aquatic and terrestrial landscapes of the McMurdo Dry Valleys, Antarctica, ecosystem stoichiometry ranges from values near the Redfield ratios for C:N:P to nutrient concentrations in proportions far above or below ratios necessary to support balanced microbial growth. This polar desert provides an opportunity to evaluate stoichiometric approaches to understand nutrient cycling in an ecosystem where biological diversity and activity are low, and controls over the movement and mass balances of nutrients operate over 10–10⁶ years. The simple organisms (microbial and metazoan) comprising dry valley foodwebs adhere to strict biochemical requirements in the composition of their biomass, and when activated by availability of liquid water, they influence the chemical composition of their environment according to these ratios. Nitrogen and phosphorus varied significantly in terrestrial and aquatic ecosystems occurring on landscape surfaces across a wide range of exposure ages, indicating strong influences of landscape development and geochemistry on nutrient availability. Biota control the elemental ratio of stream waters, while geochemical stoichiometry (e.g., weathering, atmospheric deposition) evidently limits the distribution of soil invertebrates. We present a conceptual model describing transformations across dry valley landscapes facilitated by exchanges of liquid water and biotic processing of dissolved nutrients. We conclude that contemporary ecosystem stoichiometry of Antarctic Dry Valley soils, glaciers, streams, and lakes results from a combination of extant biological processes superimposed on a legacy of landscape processes and previous climates

The Molecular Diversity of Freshwater Picoeukaryotes Reveals High Occurrence of Putative Parasitoids in the Plankton

Eukaryotic microorganisms have been undersampled in biodiversity studies in freshwater environments. We present an original 18S rDNA survey of freshwater picoeukaryotes sampled during spring/summer 2005, complementing an earlier study conducted in autumn 2004 in Lake Pavin (France). These studies were designed to detect the small unidentified heterotrophic flagellates (HF, 0.6–5 µm) which are considered the main bacterivores in aquatic systems. Alveolates, Fungi and Stramenopiles represented 65% of the total diversity and differed from the dominant groups known from microscopic studies. Fungi and Telonemia taxa were restricted to the oxic zone which displayed two fold more operational taxonomic units (OTUs) than the oxycline. Temporal forcing also appeared as a driving force in the diversification within targeted organisms. Several sequences were not similar to those in databases and were considered as new or unsampled taxa, some of which may be typical of freshwater environments. Two taxa known from marine systems, the genera Telonema and Amoebophrya, were retrieved for the first time in our freshwater study. The analysis of potential trophic strategies displayed among the targeted HF highlighted the dominance of parasites and saprotrophs, and provided indications that these organisms have probably been wrongfully regarded as bacterivores in previous studies. A theoretical exercise based on a new ‘parasite/saprotroph-dominated HF hypothesis’ demonstrates that the inclusion of parasites and saprotrophs may increase the functional role of the microbial loop as a link for carbon flows in pelagic ecosystems. New interesting perspectives in aquatic microbial ecology are thus opened

The changing form of Antarctic biodiversity

Antarctic biodiversity is much more extensive, ecologically diverse and biogeographically structured than previously thought. Understanding of how this diversity is distributed in marine and terrestrial systems, the mechanisms underlying its spatial variation, and the significance of the microbiota is growing rapidly. Broadly recognizable drivers of diversity variation include energy availability and historical refugia. The impacts of local human activities and global environmental change nonetheless pose challenges to the current and future understanding of Antarctic biodiversity. Life in the Antarctic and the Southern Ocean is surprisingly rich, and as much at risk from environmental change as it is elsewher