Control of Antarctic phytoplankton community composition and standing stock by light availability

Southern Ocean phytoplankton are especially subjected to pronounced seasonal and interannual changes in light availability. Although previous studies have examined the role of light in these environments, very few combined pigment-based taxonomy with flow cytometry to better discriminate the light response of various phytoplankton groups. In particular the different populations within the diverse and important taxonomic group of diatoms require further investigation. Six incubation experiments (9–10 days) were performed during the main productive period with natural seawater collected at the Western Antarctic Peninsula. Standing stock of Phaeocystis spp. cells displayed relatively fast accumulation under all levels of light (low, medium, high; 4–7, 30–50 and 150–200 µmol quanta m−2 s−1), whilst the small- and larger-sized diatom populations (4.5 and 20 µm diameter) exhibited faster accumulation in medium and high light. In contrast, intermediate-sized diatoms (11.5 µm diameter) displayed fastest net growth under low light, subsequently dominating the phytoplankton community. Low light was a key factor limiting accumulation and peak phytoplankton biomass, except one incubation displaying relatively high accumulation rates under low light. The 3-week low-light period prior to experimentation likely allowed adaptation to maximize achievable growth and seems a strong determinant of whether the different natural Antarctic phytoplankton populations sustain, thrive or decline. Our study provides improved insight into how light intensity modulates the net response of key Antarctic phytoplankton, both between and within taxonomic groups

Antarctic phytoplankton community composition and size structure: importance of ice type and temperature as regulatory factors

Climate change at the Western Antarctic Peninsula (WAP) is predicted to cause major changes in phytoplankton community composition, however, detailed seasonal field data remain limited and it is largely unknown how (changes in) environmental factors influence cell size and ecosystem function. Physicochemical drivers of phytoplankton community abundance, taxonomic composition and size class were studied over two productive austral seasons in the coastal waters of the climatically sensitive WAP. Ice type (fast, grease, pack or brash ice) was important in structuring the pre-bloom phytoplankton community as well as cell size of the summer phytoplankton bloom. Maximum biomass accumulation was regulated by light and nutrient availability, which in turn were regulated by wind-driven mixing events. The proportion of larger-sized (> 20 µm) diatoms increased under prolonged summer stratification in combination with frequent and moderate-strength wind-induced mixing. Canonical correspondence analysis showed that relatively high temperature was correlated with nano-sized cryptophytes, whereas prymnesiophytes (Phaeocystis antarctica) increased in association with high irradiance and low salinities. During autumn of Season 1, a large bloom of 4.5-µm-sized diatoms occurred under conditions of seawater temperature > 0 °C and relatively high light and phosphate concentrations. This bloom was followed by a succession of larger nano-sized diatoms (11.4 µm) related to reductions in phosphate and light availability. Our results demonstrate that flow cytometry in combination with chemotaxonomy and size fractionation provides a powerful approach to monitor phytoplankton community dynamics in the rapidly warming Antarctic coastal waters

Genotype-Phenotype Correlation in NF1: Evidence for a More Severe Phenotype Associated with Missense Mutations Affecting NF1 Codons 844–848

Neurofibromatosis type 1 (NF1), a common genetic disorder with a birth incidence of 1:2,000–3,000, is characterized by a highly variable clinical presentation. To date, only two clinically relevant intragenic genotype-phenotype correlations have been reported for NF1 missense mutations affecting p.Arg1809 and a single amino acid deletion p.Met922del. Both variants predispose to a distinct mild NF1 phenotype with neither externally visible cutaneous/plexiform neurofibromas nor other tumors. Here, we report 162 individuals (129 unrelated probands and 33 affected relatives) heterozygous for a constitutional missense mutation affecting one of five neighboring NF1 codons—Leu844, Cys845, Ala846, Leu847, and Gly848—located in the cysteine-serine-rich domain (CSRD). Collectively, these recurrent missense mutations affect ∼0.8% of unrelated NF1 mutation-positive probands in the University of Alabama at Birmingham (UAB) cohort. Major superficial plexiform neurofibromas and symptomatic spinal neurofibromas were more prevalent in these individuals compared with classic NF1-affected cohorts (both p < 0.0001). Nearly half of the individuals had symptomatic or asymptomatic optic pathway gliomas and/or skeletal abnormalities. Additionally, variants in this region seem to confer a high predisposition to develop malignancies compared with the general NF1-affected population (p = 0.0061). Our results demonstrate that these NF1 missense mutations, although located outside the GAP-related domain, may be an important risk factor for a severe presentation. A genotype-phenotype correlation at the NF1 region 844–848 exists and will be valuable in the management and genetic counseling of a significant number of individuals

Measurement of vector boson production cross sections and their ratios using pp collisions at √s = 13.6 TeV with the ATLAS detector

Abstract available from publisher's website

Investigating the use of milk fatty acids to detect dietary changes: a comparison with faecal analysis in Antarctic fur seals

We compared the use of fatty acid signature analysis with results from traditional faecal methods using milk samples and enemas concurrently collected from 8 female Antarctic fur seals Arctocephalus gazella foraging from Bird Island, South Georgia. The seals were serially sampled throughout the 1998/1999 breeding season, with collections taken after every foraging trip when possible. The total lipid content of the milk increased throughout the season. A general linear model using 4 principal components showed that it was the point within the breeding season at which a milk sample was collected that had the biggest influence on its fatty acid composition. There were also significant differences in the milk composition of individual seals. However, the results of faecal analysis, which are themselves subject to potential biases, were not correlated with the relative amounts of individual fatty acids. It has been suggested that seasonal changes in the milk fatty acids, previously observed in the same population of seals, are a result of increased consumption of fish. We found no evidence of this in the faecal material and suggest that the seasonal variability may be a result of changes in the fatty acid composition of the seals’ main prey (krill), or because of the changing needs of the developing pups. This study highlights the need for comprehensive testing of milk fatty acid signature analysis before the full potential of this technique can be realised

Stoichiometric theory extended to micronutrients: comparison of the roles of essential fatty acids, carbon, and nitrogen in the nutrition of marine copepods

Conventional stoichiometric theory, which is used to study the limitation of zooplankton production by C, N, and other elements, is extended to include the essential polyunsaturated fatty acids (PUFAs) 20:5(n-3) and 22:6(n-3). Using typical biochemical compositions of consumer (Calanus helgolandicus) and algal food (hypothetical diatom-dinoflagellate mixtures), the analysis shows that PUFAs or macronutrients can be important in limiting zooplankton production, depending on the biochemical compositions of consumer and food and the efficiencies with which dietary components are used. Predicted limitation by fatty acids is strongest when zooplankton use a monospecific diet, indicating that such limitation may be of particular significance in laboratory zooplankton, which are often fed phytoplankton monocultures. The analysis illustrates several factors that operate to minimize the limiting potential of fatty acids to the extent that limitation by C or N could occur: selective grazing to obtain a nutritionally balanced diet, plasticity in consumer biochemical composition, and high C requirements for respiration. The possibility of macronutrient limitation is increased further if zooplankton are able to actively synthesize essential PUFAs, although this is not thought to be the case in most aquatic systems. The work highlights the need for complete data sets incorporating fatty acids and bulk elemental properties of consumers and prey, as well as an improved understanding of the roles and cycling of essential fatty acids, if we are to be able to provide a unified view of zooplankton nutrition

Antarctic benthic foraminfera facilitate rapid cycling of phytoplankton-derived organic carbon

Fatty acid biomarker analyses of Cassidulina crassa, a dominant calcareous foraminieran at 55-m water depth in Arthur Harbor, Anvers Island (64°46′S, 64°04′W), Antarctica, revealed that this species responds rapidly to the deposition of fresh phytoplankton material from the overlying water column. During the sampling period in January/February 2002, a late summer phytoplankton bloom was clearly reflected in the fatty acid composition of C. crassa. This was apparent in the significant short-term increase of the relative content in polyunsaturated fatty acids, which more than doubled within the short period of one week from just over 14% on 28/29 January to 32% on 6 February. C. crassa feeds selectively on the high quality part of deposited organic matter, is highly abundant and widely distributed around the Antarctic, and has a wide bathymetric range. The present study shows that this species, like other, similar Antarctic benthic foraminiferal species such as Globocassidulina subglobosa, plays an important role in the rapid cycling of phytoplankton-derived organic carbon in Antarctic marine environments