Genetic diversity and ecology of the planktonic foraminifers Globigerina bulloides , Turborotalita quinqueloba and Neogloboquadrina pachyderma off the Oman margin during the late SW Monsoon

The molecular work was funded by an Advanced Fellowship award to K. Darling (UK Natural Environment Research Council (NERC); NER/J/S/2000/00860 and NE/D009707/1). SA received support from a DAAD fellowship (A0998101) and HS was supported by a DFG grant (SCHU 1605/2-1).The tropical waters of the Arabian Sea are among the richest biological areas of the world. The highly complex monsoonal system is particularly challenging for palaeoenvironmental study, which relies heavily upon understanding the modern-day ecology of planktonic foraminiferal assemblages and their geochemical signatures throughout the monsoonal cycle. Major upwelling responders such as G. bulloides, T. quinqueloba and N. pachyderma, typically associated with cooler mid to higher latitude ecosystems, are also found in number in the tropical Arabian Sea. Due to the more usual cooler water affinity of these morphospecies, the oceanographically isolated tropical upwelling ecosystem of the Arabian Sea potentially harbours new ecologically distinct genotypes (ecotypes). Samples were collected off the Oman margin at 15 stations towards the end of the summer monsoon to determine the genetic profiles of these morphospecies in both upwelling and open ocean regimes. Phylogenetic analysis of their small subunit (SSU) rDNA sequences revealed several new genetically distinct ecotypes. Two genetically divergent ecotypes of G. bulloides (Types Ia and IIf) were identified along the cruise track. Type Ia, a member of the G. bulloides warm water lineage, was found in both the upwelling and open ocean regions. The second genotype (IIf), a member of the G. bulloides cool water lineage, was found only in more marginal late upwelling cooler waters. Initial visual assessment of G. bulloides images suggests that it may be morphologically cryptic. Two highly divergent genotypes of T. quinqueloba (Types Ib and IIe) were also identified, which were largely confined to the eastern and northern Arabian Sea. Type IIe is a new member of the T. quinqueloba cool water lineage which points to its potential cool water affinity, but genotyping numbers are too low to confirm a specific association with upwelling. A new highly divergent genotype of N. pachyderma (Type VIII) was also identified at the western and southern stations. Comparison of global upwelling system genotype assemblages currently indicate little regional commonality. This complicates regional palaeoproxy understanding, since geochemical calibrations are known to be species and genotype specific. Detailed studies of the ecology and diversity of genotypes within each system should therefore be carried out to ensure the accuracy of palaeorecord interpretation.Publisher PDFPeer reviewe

Zooplankton-mediated nutrient limitation patterns in marine phytoplankton: an experimental approach with natural communities

International audienceZooplankton nutrient recycling has been shown to substantially affect nutrient availability for phytoplankton. However, investigations are required to determine whether zooplankton also influence nutrient limitation in marine phytoplankton communities, and whether grazing by different zooplankton groups results in different patterns of phytoplankton nutrient limitation. We performed laboratory experiments under different nutrient supply conditions on a variety of phytoplankton communities with natural densities of copepods and rotifers, and tested phytoplankton nutrient limitation in bioassays for nitrogen, phosphorus, and the combination of the two. After 5 d incubation with zooplankton, we observed a significant increase in phytoplankton biomass in the zooplankton treatments. We relate this largely to nutrient recycling effects, which are amplified through possible trophic cascade effects. In copepod treatments, the highest phytoplankton biomass was reached under Redfield and nitrogen excess nutrient supply conditions, while the highest biomass in rotifer treatments was registered under phosphorus excess conditions. In most cases, nutrient limitation assays revealed a co-limitation of phytoplankton by nitrogen and phosphorus. With increasing nitrogen supply, we observed an increase in phosphorus limitation in the copepod treatments and a decrease in nitrogen limitation in the rotifer treatments. The phytoplankton community was driven into phosphorus limitation under nitrogen excess conditions in copepod treatments. Our results indicate that natural densities of zooplankton are able to promote nitrogen and phosphorus co-limitation in phytoplankton communities

Planktic foraminifera census count data from sediment samples from the Red Sea

The Red Sea is an extreme marine environment, with conditions limiting the application of standard geochemical proxies for the reconstruction of paleoclimate. In order to develop paleoenvironmental reconstruction methods which are not dependent on chemical signals, we investigated the distribution of planktonic foraminifera in the surface sediments and assessed the viability of constructing foraminiferal transfer functions in this basin. We find a distinct gradient in the faunal assemblage along the basin's axis, which is reflected in a high correlation between faunal composition and all considered environmental parameters (temperature, salinity, chlorophyll a concentration, stratification, and oxycline depth). As a result, transfer functions constructed by different methods (ANN, MAT, IKM, WA-PLS) appear to be able to estimate all of these parameters with a high average accuracy (15% of the parameter's range in the Red Sea). However, redundancy analysis of the distribution of foraminiferal assemblages in surface sediments alone did not yield unambiguous results in terms of which of the considered factors exerts a primary control on the foraminifera distribution and which of the observed relationships are the result of the mutual correlation among the environmental factors. To disentangle the effect of individual environmental parameters, we applied the obtained transfer functions on a newly generated Holocene record from the central Red Sea. The integration of published paleoclimate reconstructions with our data allowed us to identify productivity as the most likely primary control of the planktonic foraminifera distribution in the Red Sea. The generated transfer functions can estimate paleoproductivity with acceptable accuracy (RMSEP chlorophyll a = 0.1 mg/m**3; ~ 8% of recent range), but only under such conditions in the past when circulation patterns and salinity levels in the basin were fundamentally comparable to the present day. Since productivity in the central and southern Red Sea is closely linked with the Monsoon-driven water exchange across the Strait of Bab al Mandab, the resulting reconstructions can provide indirect information on the mode and intensity of the monsoonal system in the past

Nitrogen enrichment leads to changing fatty acid composition of phytoplankton and negatively affects zooplankton in a natural lake community

Secondary production in freshwater zooplankton is frequently limited by the food quality of phytoplankton. One important parameter of phytoplankton food quality are essential polyunsaturated fatty acids (PUFAs). Since the fatty acid composition of phytoplankton is variable and depends on the algae's nutrient supply status, inorganic nutrient supply may affect the algal PUFA composition. Therefore, an indirect transfer of the effects of nutrient availability on zooplankton by changes in algal PUFA composition is conceivable. While the phosphorus (P) supply in lakes is largely decreasing, nitrogen (N) inputs continue to increase. This paper presents data from a mesocosm field experiment in which we exposed phytoplankton communities to increasing N enrichment. As a consequence, the PUFA composition of the phytoplankton community changed. With increasing nitrogen fertilisation, we observed lower quantities of essential PUFAs, together with a decrease in the abundances of the dominant herbivorous zooplankton Daphnia sp. Their biomass was significantly correlated with phytoplankton PUFA content (C18:3 omega 3, C20:5 omega 3, C18:2 omega 6). Our data therefore indicate that changes in nitrogen supply, together with the resultant changes in phytoplankton food quality, can negatively affect the secondary production of herbivorous zooplankton by reducing the availability of essential polyunsaturated fatty acids

Global Warming and Continued External Loading Alters Nitrogen and Phosphorus Balance in the Franconian Lake District

<p>Data belonging to Limnology and Oceanography upload:</p> <p>Global Warming and Continued External Loading Alters Nitrogen and Phosphorus Balance in a Temperate Reservoir System.</p> <p>Global warming will intensify in the coming century. Consequently cycling of phosphorus and nitrogen in reservoirs will be affected which could lead to aggravated phytoplankton blooms. For now few case studies have simultaneously investigated effects of warming on cycling of both nitrogen and phosphorus. In this context, the study focused on the Franconian Lake District’s four reservoirs, covering the period from 2000 to 2019. Changes in water temperatures (which increased by 0.3 to 1°C annually), the extension of thermal stratification (9 to 19 days per decade) and hypolimnetic anoxia (14 to 36 days per decade) were determined. These shifts led to decreases in nitrogen concentrations but increases in phosphorus concentrations. Increased denitrification rates reduced nitrogen levels early in the year and ammonification in the anoxic hypolimnia showed only marginal increases, not compensating for denitrification losses. Conversely, phosphorus concentrations increased particularly in the increasingly anoxic summer months. This was ascribed to release of ortho-phosphate from mineralization and redox-sensitive phosphorus fractions in the sediment. Opposing trends led to a sharp decrease in the total nitrogen to total phosphorus (TN:TP) ratios. The study also revealed an increase in bio-available ortho-phosphate and ammonium. Combined the altered nutrient composition could lead to proliferation of bloom-forming, nitrogen-fixing diazotrophic cyanobacteria. This study suggests that most temperate reservoirs and lakes, suffering from ongoing external and internal nutrient loads, will probably experience further reductions in TN:TP-ratio in a warmer world. To mitigate indirect effects of warming, new strategies are required to decrease phosphorus inflows and manage legacy phosphorus release from sediments.</p&gt